Cython Changelog

3.1.6 (2025-10-23)

Bugs fixed

• Unicode characters formatted from C integers with f"{value:c}" could result in invalid Python string objects since Cython 3.1.0. (Github issue #7240)

• cythonize (program and function) now uses concurrent.futures.ProcessPoolExecutor instead of multiprocessing.Pool to fix a hang on build failures in parallel builds. A possible work-around is to disable parallel builds. Patch by Sviatoslav Sydorenko. (Github issue #7183)

3.1.5 (2025-10-20)

Bugs fixed

• Conversion from C++ strings longer than PY_SSIZE_T_MAX did not validate the length.

• Some non-Limited API code was incorrectly used in generated header files. (Github issue #7157)

• Optimised unpacking of Python integers in expressions uses a slightly safer scheme. (Github issue #7134)

• Empty return statements were not always reported when tracing. (Github issue #7022)

• Value conversion errors when tracing C return statements no longer fail the trace but fall back to reporting None returns instead. (Github issue #6503)

3.1.4 (2025-09-16)

Features added

• Declarations for the new PyUnstable_*() refcounting C-API functions in Py3.14 were added. (Github issue #6836)

Bugs fixed

• The monitoring code could crash on tracing. (Github issue #7050)

• Initialising the monitoring code could fail with a CPython exception. See https://github.com/nedbat/coveragepy/issues/1790#issuecomment-3257410149

• Optimised integer shifting triggered undefined behaviour in C. (Github issue #7089)

• Deallocating objects that inherit from external types defined in pxd files could run into an infinite loop. (Github issue #7143)

• A reference to metaclasses could be leaked on instantiation. (Github issue #7130)

• (Unlikely) error handling during empty builtin container tests was ineffective. (Github issue #7190)

• Generated *_api.h files used potentially unknown Cython configuration macros. (Github issue #7108)

• cythonize() avoids parallel compiler runs on systems using spawn() in multiprocessing. Patch by Marcel Bargull. (Github issue #3262)

• The @cython.ufunc decorator was missing in type checker stubs. Patch by jayClean. (Github issue #7109)

3.1.3 (2025-08-13)

Bugs fixed

• Some method calls with 0 or 1 argument failed to use PyObject_VectorCallMethod().

• Walrus assignments of literal Python integers could generate invalid C code. (Github issue #6989)

• cython.pythread_type_lock (also used as fallback for cython.pymutex) could stall on heavily contended locks. (Github issue #6999)

• C string arrays (not pointers) always coerced to the Python default string type, even on explicit casts to other string types. (Github issue #7020)

• Unterminated \N{} character escapes in strings could unrail the parser. (Github issue #7056)

• An internal C function was not marked as static and leaked a linker symbol. (Github issue #6957)

• Some Unicode letters were not recognised as lexically valid name parts. (Github issue #7059)

• Compatibility with PyPy3.8 was lost by accident.

• The Linux binary wheels of 3.1.2 used SSSE3 CPU instructions which are not available on some CPUs. (Github issue #7038)

3.1.2 (2025-06-09)

Bugs fixed

• Attribute lookups failed on the bool builtin type. (Github issue #6905)

• Type checks on or-ed union types could incorrectly return false. (Github issue #6420)

• Negative list indexing could accidentally wrap around twice in PyPy and the Limited API.

• Iterating over literal sequences with starred (unpacked) items could infer a wrong type for the loop variable and fail to assign the values. (Github issue #6924)

• Calls to C functions taking exception types failed to check for a None argument. (Github issue #6420)

• Fused functions had an incorrect __module__ attribute. (Github issue #6897)

• The type of Cython implemented functions had an incorrect __module__ attribute. (Github issue #6841)

• Errors while indexing into bytearray or str in nogil sections could crash. (Github issue #6947)

• bytearray.append() could silently accept some invalid character numbers.

• The C++11 <type_traits> header was included regardless of the C++ version. (Github issue #6896)

• PyDict_GetItemStringRef() was accidentally used in older Limited API versions. (Github issue #6914)

• abort() was used but not always available in the Limited API. (Github issue #6918)

• Some dependencies were missing from the depfile. (Github issue #6938)

• Embedded function signatures were not always separated from the existing docstring. (Github issue #6904)

• numpy.math was missing from Cython/Includes/ and could not be cimported. (Github issue #6859)

• Some tests were adapted for NumPy 2.x. (Github issue #6898)

• Some C compiler warnings were fixed. (Github issue #6870)

• Cython.Build was not officially exposing the cythonize function. (Github issue #6934)

3.1.1 (2025-05-19)

Bugs fixed

• A reference leak in the async delegation code was fixed. (Github issues #6850, #6878)

• Conditional if-else expressions mixing Python and C (numeric) types could end up inferring an overly tight result type, thus leading to unexpected type conversions, runtime exceptions on assignment, or incorrect “temporary assignment” compile errors. (Github issue #6854)

• Some Limited API issues were resolved. (Github issue #6862)

• Large C long long values could be truncated when passed into PyPy. (Github issue #6890)

• callable() incorrectly reported False in PyPy for classes with metaclasses. Patch by Anatolii Aniskovych. (Github issue #6892)

• The signature of fused functions was no longer introspectable in Cython 3.1.0. (Github issue #6855)

• Coroutines could generate invalid C with line tracing enabled. (Github issue #6865)

• Code using complex() could generate invalid C code missing type declarations. (Github issue #6860)

• Code using e.g. list[int | None] outside of variable/argument annotations failed to compile. (Github issue #6856)

• Code using ctuples in a const context could generate invalid C. (Github issue #6864)

• Accessing special methods on cpdef enums failed to compile.

• Some C compiler warnings were resolved. Patches by Daniel Larraz. (Github issues #6876, #3172, #6873, #6877)

• Re-establish support for PyPy 3.8. (Github issue #6867)

3.1.0 (2025-05-08)

Other changes

• No functional changes since 3.1.0 rc 2.

3.1.0 rc 2 (2025-05-07)

Features added

• Declarations for C++ std::stop_token were added as libcpp.stop_token to provide additional low-level synchronisation primitives also in the light of free-threading Python. (Github issue #6820)

• The generation of the shared module now happens automatically from cythonize() in a setuptools build if a corresponding Extension has been configured. This avoids an additional step outside of the setup.py or pip wheel run. (Github issue #6842)

Bugs fixed

• Variables typed as builtin Python exception types now accept subtypes instead of rejecting them. This specifically impacted types like BaseException, Exception or OSError, which almost always intend to reference subtypes. (Github issue #6828)

• Functions with more than 10 constant default argument values could generate invalid C code. (Github issue #6843)

• The call_once() function argument in libc.threads (new in 3.1) was changed to require a nogil declaration, as semantically implied. Code that used it with a callback function expecting to hold the GIL must change the callback code to use with gil.

• Calling cimported C functions with their fully qualified package name could crash Cython. (Github issue #6551)

• Naming a variable after its inferred type (e.g. str += "") could trigger an infinite loop in Cython. (Github issue #6835)

• Cython is more relaxed about the exact C++ constructor name when it calls new() on ctypedefs. (Github issue #6821)

• Using cpp_locals in nogil sections could crash. (Github issue #6838)

• const struct declarations could lead to invalid assignments to const temp variables. (Github issue #6804)

• A refcounting error was fixed in the method class cell support code. (Github issue #6839)

3.1.0 rc 1 (2025-05-01)

Features added

• cython.pymutex provides a fast mutex by wrapping the new PyMutex feature of recent CPython versions (including free-threading) and falls back to PyThread locks in older Pythons. (Github issue #6579)

• A new directive subinterpreters_compatible=shared_gil/own_gil was added to allow modules to declare support for subinterpreters. (Github issue #6513)

• divmod() is also optimised for C floating point types and can be called on C number types without holding the GIL. (Github issue #6801)

• New C++ declarations were added. (Github issues #6625, #6731)

• embedsignature now works for special methods (if they have a docstring). (Github issue #1577)

Bugs fixed

• Iterating over literal sequences in generator expressions could generate invalid C code. (Github issue #6725)

• Tracing could generate invalid C code. (Github issue #6781)

• Non-ASCII function argument names could generate invalid C code. (Github issue #6813)

• Optimised divmod() calls could produce incorrect results in beta-1 due to incorrect C type usage. (Github issue #6786)

• Raising UnboundLocalError could fail for non-ascii variable names. (Github issue #6800)

• The signature of PyByteArray_Resize() in cpython.bytearray failed to propagate exceptions. Patch by Kirill Smelkov. (Github issue #6787)

• Some more issues with the Limited C-API and free-threading Python were resolved.

  https://github.com/cython/cython/issues?q=label%3A%22limited+api%22

  https://github.com/cython/cython/issues?q=label%3A%22nogil+CPython%22

• The signature of cythonize_one() accidentally changed in 3.1.0b1. (Github issue #6815)

Other changes

• Named cpdef enums no longer copy their item names into the global module namespace. This was considered unhelpful for named enums which already live in their own class namespace. In cases where the old behaviour was desired, users can add the following backwards compatible command after their enum class definition: globals().update(getattr(TheUserEnumClass, '__members__')). Anonymous enums still produce global item names, as before. (Github issue #4571)

3.1.0 beta 1 (2025-04-03)

Features added

• Global cdef const … variables are supported. (Github issue #6542)

• A new context manager / function decorator cython.critical_section was added wrapping Python’s critical section C-API feature. (Github issues #6516, #6577)

• Some common Cython-internal code (currently only memoryview related) can now be extracted into a shared extension module to reduce the installed overall size of a package with many Cython compiled modules. (Github issue #2356)

• The type of prange loop targets is now inferred. (Github issue #6585)

• Extracting keyword arguments is faster in some cases. (Github issue #6683)

• Calling divmod() on any C integer types is efficient. (Github issue #6717)

• Some async/coroutine/vectorcall code has improved fast-paths. (Github issues #6732, #6735, #6736, #6738, #6742, #6771)

• Calls to Python builtins and extension types use the vectorcall protocol. (Github issue #6744)

• Method calls use PyObject_VectorcallMethod() where possible. (Github issue #6747)

• Some C-API shortcuts were (re-)added. (Github issue #6761)

• Cython can avoid normalising exceptions in an except clause if it knows that they are unused. (Github issue #6601)

• The cython command has a new option --cache to cache generated files. (Github issue #6091)

• The cythonize command has a new option --timeit to benchmark Cython code snippets. (Github issue #6697)

• The argument parsing cygdb command was improved based on argparse. Patch by William Ayd. (Github issue #5499)

• The PyWeakref_GetRef declaration was added to cpython.weakref and backported. Patch by Lysandros Nikolaou. (Github issue #6478)

• std::span declarations were added to libcpp. Patch by Alexander Condello. (Github issue #6539)

• std::string_view declarations were added to libcpp. Patch by Antoine Pitrou. (Github issue #6539)

• Mutex declarations for libc and libcpp were added. (Github issue #6610)

• Several C++ declarations were improved and extended. Patches by Yury V. Zaytsev. (Github issues #488, #489)

• Bazel build rules were updated for better interoperability. Patch by maleo. (Github issue #6478)

• The Demos/benchmarks/ directory include a new benchmark runner that can run selected benchmarks against different Cython git revisions.

Bugs fixed

• Many issues with the Limited C-API and free-threading Python were resolved. This includes better thread-safety of Cython-internal types like functions and generators.

  https://github.com/cython/cython/issues?q=label%3A%22limited+api%22

  https://github.com/cython/cython/issues?q=label%3A%22nogil+CPython%22

• for-in loops could generate invalid code for C++ containers. Patch by Taras Kozlov. (Github issue #6578)

• PyDict_GetItemRef() and PyList_GetItemRef() were not always used correctly. Patch by Lisandro Dalcin. (Github issue #6647)

• Inlined calls to local functions could crash with binding=False. (Github issue #6556)

• Calling sorted() could crash in 3.1.0a1. (Github issue #6496)

• Calling 0-arg methods was unnecessarily slow in 3.1.0a1. (Github issue #6730)

• A crash when reading the interpreter ID was fixed.

• Crashes while tracing C function returns were resolved. (Github issue #6503)

• A compiler crash on complex/complex was resolved. (Github issue #6552)

• A compiler crash when using the cpp_locals directive was resolved. (Github issue #6370)

• Name mangling did not work correctly for attributes of extension types that have reserved C names. (Github issue #6678)

• Declaring a @staticmethod in a pxd file and overriding it in a subclass could trigger incorrect “declared but not defined” errors. Patch by Aditya Pillai. (Github issue #6714)

• Cython’s fake code objects are now compatible with GraalPython. (Github issue #6409)

• Stepping through foreign code with cygdb could fail with an IndexError. Patch by clayote. (Github issue #6552)

• Some PyPy incompatibilities were resolved. Patches by Matti Picus. (Github issue #6592, #6640)

• Interoperability with recent Pythran releases was fixed. (Github issue #6494)

• The gdb compatibility of cygdb was improved. Patch by Kent Slaney. (Github issue #6681)

• Some redundant exception normalisation work was removed in Python 3.12+. (Github issue #6599)

• A compiler hang introduced in 3.1a1 when overriding methods was resolved. Patch by Aditya Pillai. (Github issue #6704)

• A compiler crash was resolved when trying to issue a warning. Patch by Gabriele N. Tornetta. (Github issue #6711)

• Some incomplete import time “safety checks” from 3.1.0a1 were removed again. (Github issue #6671)

• Using the common_utility_include_dir option in parallel builds on Windows could fail.

• Some “unused” warnings from the C compiler were resolved. Patches by Lisandro Dalcin. (Github issue #6726)

Other changes

• All Cython-internal types (functions, coroutines, …) are now heap types and use type specs. (Github issue #6633)

• Tracing/monitoring is now disabled in parallel/prange sections. (Github issue #6709)

• The numpy.math cimport module has been deprecated. Usages should be replaced by libc.math. (Github issue #6743)

• Includes all fixes as of Cython 3.0.12.

3.1.0 alpha 1 (2024-11-08)

Features added

• Support for freethreading builds of CPython 3.13 was added. It comes with a new directive freethreading_compatible=True to mark modules as free-threading compatible (Py_mod_gil).

  https://github.com/cython/cython/issues?q=label%3A%22nogil+CPython%22

  Patches by Lysandros Nikolaou and Nathan Goldbaum. (Github issue #6162)

• Support for monitoring Cython modules via sys.monitoring in CPython 3.13+ was added. For coverage reporting, this needs to be disabled with -DCYTHON_USE_SYS_MONITORING=0 as long as coverage.py does not support sys.monitoring for coverage plugins. (Github issue #6144)

• Many issues with the Limited C-API were resolved. It is now sufficient to define the macro Py_LIMITED_API to activate the support.

  https://github.com/cython/cython/issues?q=label%3A%22limited+api%22

• Support for GraalPython was improved (but is still incomplete).

• Several issues with the gdb support were resolved. Patches by Kent Slaney. (Github issues #5955, #5948)

• typing.Union[SomeType, None] and SomeType | None are now understood and mean the same as typing.Optional[SomeType], allowing None in type checks. (Github issue #6254)

• cython.const[] and cython.volatile[] are now available as type modifiers in Python code. (Github issue #5728)

• cython.pointer[SomeCType] can now be used to define pointer types in Python type annotations. (Github issue #5071)

• Several improvements were made to reduce the size of the resulting extension modules. (Github issue #4425)

• Function calls now use the PEP-590 Vectorcall protocol, even when passing keyword arguments. (Github issues #5804)

• Coroutines now use the am_send slot function instead of going through a Python .send() call. This has been backported for Python 3.7 - 3.9. (Github issues #4585)

• __set_name__ is called when assigning to class attributes. (Github issue #6179)

• Most builtin methods now provide their return type for type inference. (Github issues #4829, #5865, #6412)

• Method calls on builtin literal values are evaluated at compile time, if applicable. (Github issue #6383)

• The Python int type now maps directly to PyLong and is inferred accordingly. (Github issue #4237)

• Integer operations on known int types are faster. (Github issue #5785)

• f-strings are faster in some cases. (Github issues #5866, #6342, #6383)

• divmod() is faster on C int. Patch by Tong He. (Github issue #6073)

• dict.pop() is faster in some cases. (Github issue #5911)

• .isprintable() is optimised for Unicode characters. (Github issue #3277)

• x in () and similar tests against empty constant sequences (e.g. in generated code) are now discarded if they have no side-effects. (Github issue #6288)

• Constant (non-GC) Python objects are no longer traversed with Py_VISIT() during GC runs. (Github issue #6277)

• C++ classes implemented in Cython can now use method overloading. Patch by samaingw. (Github issue #3235)

• Assigning a Python container to a C++ vector now makes use of __length_hint__ to avoid reallocations. Patch by Denis Lukianov. (Github issue #6077)

• The C++11 emplace* methods were added to libcpp.deque. Patch by Somin An. (Github issue #6159)

• cpython.time was updated and extended for Python 3.13. (Github issue #6187)

• Dataclasses support the match_args option. (Github issue #5381)

• Threading in parallel sections can now be disabled with a new use_threads_if condition. (Github issue #5919)

• New options warn.deprecated.DEF and warn.deprecated.IF can silence the deprecation warnings. Patch by Eric Larson. (Github issue #6243)

• cygdb shows more helpful output for some objects. Patch by Kent Slaney. (Github issue #5958)

• Bazel build support for improved. Patch by mering. (Github issue #6452)

• The parser was updated for Unicode 15.1 (as provided by CPython 3.13b4).

Bugs fixed

• C functions used different start lines and columns for error reporting and tracing than Python functions. They now use the line and column of their first decorator or (if none) their definition line, as in Python. (Github issue #6366)

• Dataclasses did not handle default fields without init value correctly. (Github issue #5858)

• Implementing a special method based on another could lead to infinite recursion. (Github issue #5863)

• The __class__ cell variable in methods was not always working as in Python. Initial patch by Tom Keefe. (Github issue #2912)

• Lambda functions had no code objects. Their signature can now be introspected. (Github issue #2983)

• Subtyping complex as extension type could fail. (Github issue #6346)

• hasattr() now propagates exceptions that occur during lookup. (Github issue #6269)

• The base type of extension heap types is now traversed during GC runs in Py3.9+. (Github issue #4193)

• The Python & operator could touch invalid memory with certain 0 values in Python <= 3.10. Patch by Michael J. Sullivan. (Github issue #4193)

• Exception values were not always recognised as equal at compile time. (Github issue #5709)

• Running Cython in different Python versions could generate slightly different C code due to differences in the builtins. (Github issue #5591)

• The common_include_dir feature used different file paths in the C code on Windows and Posix. It now uses forward slashes as directory separator consistently. (Github issue #6355)

• File paths in the C code are now relative to the build directory. Patch by Oscar Benjamin. (Github issue #6341)

• depfiles now use relative paths whenever possible. Patch by Loïc Estève. (Github issue #6345)

• The -a option in the IPython magic no longer copies the complete HTML document into the notebook but only a more reasonable content snippet. Patch by Min RK. (Github issue #5760)

• Uselessly referring to C enums (not enum values) as Python objects is now rejected. Patch by Vyas Ramasubramani. (Github issue #5638)

• Cython no longer acquires the GIL during in-place assignments to C attributes in nogil sections. Patch by Mads Ynddal. (Github issue #6407)

• Several C++ warnings about char* casts were resolved. (Github issues #5515, #5847)

• C++ undefined behaviour was fixed in an error handling case. (Github issue #5278)

• Dict assignments to struct members with reserved C/C++ names could generate invalid C code.

• The PEP-479 implementation could raise a visible RuntimeError without a trace of the original StopIteration. (Github issue #5953)

• A crash was fixed when assigning a zero-length slice to a memoryview. Patch by Michael Man. (Github issue #6227)

• Conditionally assigning to variables with the walrus operator could crash. (Github issue #6094)

• Unterminated string literals could lock up the build in an infinite loop. (Github issue #5977)

• Exporting C functions uses better platform compatible code. (Github issue #4683)

• The shebang in libpython.py was incorrect. Patch by Luke Hamburg. (Github issue #6439)

• Cython now uses SHA-256 instead of SHA-1 for caching etc. as the latter may not be available on all Python installations. (Github issue #6354)

Other changes

• Support for Python 2.7 - 3.7 was removed, along with large chunks of legacy code. (Github issue #2800)

• The pxd files cpython.int, cpython.cobject, cpython.oldbuffer and cpython.string were removed as they refer to C-API declarations that are only in Python 2.x. (Github issue #5870)

• The generated C code now requires a C99 compatible C compiler.

• language_level=3 is now the default. language_level=3str has become a legacy alias. (Github issue #5827)

• The Py2 types unicode and basestring are now deprecated and have become aliases of the str type. (Github issue #6374)

• Docstrings now strip their leading whitespace according to PEP-257. Patch by Lawrence Mitchell. (Github issue #6241)

• Type checkers should have it easier to find and validate Cython types in .py files. (Github issue #4327)

• The previously shipped NumPy C-API declarations (cimport numpy) were removed. NumPy has been providing version specific declarations for several versions now. (Github issue #5842)

• Usages of the outdated WITH_THREAD macro guard were removed. (Github issue #5812)

• The options for showing the C code line in Python exception stack traces were cleaned up. Previously, disabling the option with the CYTHON_CLINE_IN_TRACEBACK macro did not reduce the code overhead of the feature, and the c_line_in_traceback compile option was partly redundant with the C macro switches and lead to warnings about unused code. Since this is considered mostly a debug feature, the new default is that it is _disabled_ to avoid code and runtime overhead. It can be enabled by setting the C macro to 1, and a new macro CYTHON_CLINE_IN_TRACEBACK_RUNTIME was added that controls the runtime configurable setting if the feature is enabled, which was previously only available through the compile option. The compile option is now deprecated (but still available), and users should migrate to using the two C macros only. (Github issue #6036)

• Includes all fixes as of Cython 3.0.11 (but generates C99 code in some places).

3.0.12 (2025-02-11)

Bugs fixed

• Release 3.0.11 introduced some incorrect noexcept warnings. (Github issue #6335)

• Conditional assignments to variables using the walrus operator could crash. (Github issue #6094)

• Dict assignments to struct members with reserved C names could generate invalid C code.

• Fused ctuples with the same entry types but different sizes could fail to compile. (Github issue #6328)

• In Py3, pyximport was not searching sys.path when looking for importable source files. (Github issue #5615)

• Using & 0 on integers produced with int.from_bytes() could read invalid memory on Python 3.10. (Github issue #6480)

• Modules could fail to compile in PyPy 3.11 due to missing CPython specific header files. Patch by Matti Picus. (Github issue #6482)

• Minor fix in C++ partial_sum() declaration.

3.0.11 (2024-08-05)

Features added

• The C++11 emplace* methods were added to libcpp.deque. Patch by Somin An. (Github issue #6159)

Bugs fixed

• The exception check value of functions declared in pxd files was not always applied in 3.0.10. (Github issue #6122)

• A crash on exception deallocations was fixed. (Github issue #6022)

• A crash was fixed when assigning a zero-length slice to a memoryview. Patch by Michael Man. (Github issue #6227)

• libcpp.optional.value() could crash if it raised a C++ exception. Patch by Alexander Condello. (Github issue #6190)

• The return type of str() was mishandled, leading to crashes with language_level=3. (Github issue #6166)

• bytes.startswith/endswith() failed for non-bytes substrings (e.g. bytearray). (Github issue #6168)

• Fused ctuples crashed Cython. (Github issue #6068)

• A compiler crash was fixed when using extension types in fused types. (Github issue #6204)

• The module cleanup code was incorrect for globally defined memory view slices. (Github issue #6276)

• Some adaptations were made to enable compilation in Python 3.13. (Github issues #5997, #6182, #6251)

3.0.10 (2024-03-30)

Bugs fixed

• Cython generated incorrect self-casts when directly calling final methods of subtypes. Patch by Lisandro Dalcin. (Github issue #2747)

• Internal C names generated from C function signatures could become too long for MSVC. (Github issue #6052)

• The noexcept warnings could be misleading in some cases. Patch by Gonzalo Tornaría. (Github issue #6087)

• The @cython.ufunc implementation could generate incomplete C code. (Github issue #6064)

• The libcpp.complex declarations could result in incorrect C++ code. Patch by Raffi Enficiaud. (Github issue #6037)

• Several tests were adapted to work with both NumPy 1.x and 2.0. Patch by Matti Picus. (Github issues #6076, #6100)

• C compiler warnings when the freelist implementation is disabled (e.g. on PyPy) were fixed. It can now be disabled explicitly with the C macro guard CYTHON_USE_FREELISTS=0. (Github issue #6099)

• Some C macro guards for feature flags were missing from the NOGIL Python configuration.

• Some recently added builtins were unconditionally looked up at module import time (if used by user code) that weren’t available on all Python versions and could thus fail the import.

• A performance hint regarding exported pxd declarations was improved. (Github issue #6001)

3.0.9 (2024-03-05)

Features added

• Assigning const values to non-const variables now issues a warning. (Github issue #5639)

• Using noexcept on a function returning Python objects now issues a warning. (Github issue #5661)

• Some C-API usage was updated for the upcoming CPython 3.13. Patches by Victor Stinner et al. (Github issues #6003, #6020)

• The deprecated Py_UNICODE type is no longer used, unless required by user code. (Github issue #5982)

• std::string.replace() declarations were added to libcpp.string. Patch by Kieran Geary. (Github issue #6037)

Bugs fixed

• Cython generates incorrect (but harmless) self-casts when directly calling final methods of subtypes. Lacking a better solution, the errors that recent gcc versions produce have been silenced for the time being. Original patch by Michał Górny. (Github issue #2747)

• Unused variable warnings about clineno were fixed when C lines in tracebacks are disabled. (Github issue #6035)

• Subclass deallocation of extern classes could crash if the base class uses GC. Original patch by Jason Fried. (Github issue #5971)

• Type checks for Python memoryview could use an invalid C function. Patch by Xenia Lu. (Github issue #5988)

• Calling final fused functions could generate invalid C code. (Github issue #5989)

• Declaring extern enums multiple times could generate invalid C code. (Github issue #5905)

• pyximport used relative paths incorrectly. Patch by Stefano Rivera. (Github issue #5957)

• Running Cython with globbing characters ([]*?) in the module search path could fail. Patch by eewanco. (Github issue #5942)

• Literal strings that include braces could change the C code indentation.

Other changes

• The “enum class not importable” warning is now only issued once per enum type. (Github issue #5941)

3.0.8 (2024-01-10)

Bugs fixed

• Using const together with defined fused types could fail to compile. (Github issue #5230)

• A “use after free” bug was fixed in parallel sections. (Github issue #5922)

• Several types were not available as cython.* types in pure Python code.

• The generated code is now correct C89 again, removing some C++ style // comments and C99-style declaration-after-code code ordering. This is still relevant for some ols C compilers, specifically ones that match old Python 2.7 installations.

3.0.7 (2023-12-19)

Bugs fixed

• In the iterator of generator expressions, await and yield were not correctly analysed. (Github issue #5851)

• cpdef enums with the same name cimported from different modules could lead to invalid C code. (Github issue #5887)

• Some declarations in cpython.unicode were fixed and extended. (Github issue #5902)

• Compiling fused types used in pxd files could crash Cython in Python 3.11+. (Github issues #5894, #5588)

• Source files with non-ASCII file names could crash Cython. (Github issue #5873)

• Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.37 (2023-12-18) release.

3.0.6 (2023-11-26)

Features added

• Fused def function dispatch is a bit faster.

• Declarations for the wchar PyUnicode API were added. (Github issue #5836)

• The Python “nogil” fork is now also detected with the new Py_GIL_DISABLED macro. Patch by Hugo van Kemenade. (Github issue #5852)

Bugs fixed

• Comparing dataclasses could give different results than Python. (Github issue #5857)

• float(std::string) generated invalid C code. (Github issue #5818)

• Using cpdef functions with cimport_from_pyx failed. (Github issue #5795)

• A crash was fixed when string-formatting a Python value fails. (Github issue #5787)

• On item access, Cython could try the sequence protocol before the mapping protocol in some cases if an object supports both. (Github issue #5776)

• A C compiler warning was resolved. (Github issue #5794)

• Complex numbers failed to compile in MSVC with C11. Patch by Lysandros Nikolaou. (Github issue #5809)

• Some issues with the Limited API and with PyPy were resolved. (Github issues #5695, #5696)

• A C++ issue in Python 3.13 was resolved. (Github issue #5790)

• Several directives are now also available (as no-ops) in Python code. (Github issue #5803)

• An error message was corrected. Patch by Mads Ynddal. (Github issue #5805)

3.0.5 (2023-10-31)

Features added

• Preliminary support for CPython 3.13a1 was added to allow early testing. (Github issue #5767)

Bugs fixed

• A compiler crash was fixed. (Github issue #5771)

• A typo in the always_allow_keywords directive for Python code was fixed. Patch by lk-1984. (Github issue #5772)

• Some C compiler warnings were resolved. Patch by Pierre Jolivet. (Github issue #5780)

3.0.4 (2023-10-17)

Features added

• A new compiler directive show_performance_hints was added to disable the newly added performance hint output. (Github issue #5748)

Bugs fixed

• `cythonize` required ``distutils even for operations that did not build binaries. (Github issue #5751)

• A regression in 3.0.3 was fixed that prevented calling inline functions from another inline function in .pxd files. (Github issue #5748)

• Some C compiler warnings were resolved. Patch by Pierre Jolivet. (Github issue #5756)

3.0.3 (2023-10-05)

Features added

• More warnings were added to help users migrate and avoid bugs. (Github issue #5650)

• A warning-like category for performance hints was added that bypasses -Werror. (Github issue #5673)

• FastGIL now uses standard thread_local in C++. (Github issue #5640)

• reference_wrapper was added to libcpp.functional. Patch by Vyas Ramasubramani. (Github issue #5671)

• The cythonize command now supports the --cplus option known from the cython command. (Github issue #5736)

Bugs fixed

• Performance regressions where the GIL was needlessly acquired were fixed. (Github issues #5670, #5700)

• A reference leak for exceptions in Python 3.12 was resolved. Patch by Eric Johnson. (Github issue #5724)

• fastcall calls with keyword arguments generated incorrect C code. (Github issue #5665)

• Assigning the type converted result of a conditional (if-else) expression to int or bool variables could lead to incorrect C code. (Github issue #5731)

• Early (unlikely) failures in Python function wrappers no longer set a traceback in order to simplify the C code flow. Being mostly memory allocation errors, they probably would never have created a traceback anyway. (Github issue #5681)

• Relative cimports from packages with __init__.py files could fail. (Github issue #5715)

• Several issues with the Limited API support were resolved. (Github issues #5641, #5648, #5689)

• The code generated for special-casing both Cython functions and PyCFunctions was cleaned up to avoid calling C-API functions that were not meant for the other type respectively. This could previously trigger assertions in CPython debug builds and now also plays better with the Limited API. (Github issues #4804, #5739)

• Fix some C compiler warnings. Patches by Ralf Gommers, Oleksandr Pavlyk, Sebastian Koslowski et al. (Github issues #5651, #5663, #5668, #5717, #5726, #5734)

• Generating gdb debugging information failed when using generator expressions. Patch by Oleksandr Pavlyk. (Github issue #5552)

• Passing a setuptools.Extension into cythonize() instead of a distutils.Extension could make it miss the matching extensions.

• cython -M needlessly required distutils, which made it fail in Python 3.12. (Github issue #5681)

Other changes

• The visible deprecation warning for DEF was removed again since it proved difficult for some users to migrate away from it. The statement is still meant to be removed at some point (and thus, like IF, should not be used in new code), but the time for sunset is probably not around the corner. (Github issue #4310)

• The np_pythran option raise a DeprecationWarning if it receives other values than True and False. This will eventually be disallowed (in line with all other boolean options).

3.0.2 (2023-08-27)

Bugs fixed

• Using None as default value for arguments annotated as int could crash Cython. (Github issue #5643)

• Default values of fused types that include complex could generate invalid C code with -DCYTHON_CCOMPLEX=0. (Github issue #5644)

• Using C++ enum class types in extension type method signatures could generate invalid C code. (Github issue #5637)

3.0.1 (2023-08-25)

Features added

• The error messages regarding exception declarations were improved in order to give better help about possible reasons and fixes. (Github issue #5547)

Bugs fixed

• Memory view types in Python argument annotations no longer accept None. They now require an explicit Optional[] or a None default value in order to allow None to be passed. This was an oversight in the 3.0.0 release and is a BACKWARDS INCOMPATIBLE change. However, since it only applies to code using Python syntax, it probably only applies to newly written code that was written for Cython 3.0 and can easily be adapted. In most cases, we expect that this change will avoid bugs in user code rather than produce problems. (Github issue #5612)

• nogil functions using parallel code could freeze when called with the GIL held. (Github issues #5564, #5573)

• Relative cimports could end up searching globally and find the same package installed elsewhere, potentially in another version. (Github issue #5511)

• Attribute lookups on known standard library modules could accidentally search in the module namespace instead. (Github issue #5536)

• Using constructed C++ default arguments could generate invalid C++ code. (Github issue #5553)

• libcpp.memory.make_unique() was lacking C++ exception handling. (Github issue #5560)

• Some non-public and deprecated CAPI usages were replaced by public (and thus more future proof) API code.

• Many issues with the Limited API support were resolved. Patches by Lisandro Dalcin et al. (Github issues #5549, #5550, #5556, #5605, #5617)

• Some C compiler warnings were resolved. Patches by Matti Picus et al. (Github issues #5557, #5555)

• Large Python integers are now stored in hex instead of decimal strings to work around security limits in Python and generally speed up their Python object creation.

• NULL could not be used as default for fused type pointer arguments. (Github issue #5554)

• C functions that return pointer types now return NULL as default exception value. Previously, calling code wasn’t aware of this and always tested for raised exceptions. (Github issue #5554)

• Untyped literal default arguments in fused functions could generate invalid C code. (Github issue #5614)

• C variables declared as const could generate invalid C code when used in closures, generator expressions, ctuples, etc. (Github issues #5558, #5333)

• Enums could not refer to previously defined enums in their definition. (Github issue #5602)

• The Python conversion code for anonymous C enums conflicted with regular int conversion. (Github issue #5623)

• Using memory views for property methods (and other special methods) could lead to refcounting problems. (Github issue #5571)

• Star-imports could generate code that tried to assign to constant C macros like PY_SSIZE_T_MAX and PY_SSIZE_T_MIN. Patch by Philipp Wagner. (Github issue #5562)

• CYTHON_USE_TYPE_SPECS can now be (explicitly) enabled in PyPy.

• The template parameter “delimeters” in the Tempita Template class was corrected to “delimiters”. The old spelling is still available in the main template API but now issues a DeprecationWarning. (Github issue #5608)

• The cython --version output is now less likely to reach both stdout and stderr. Patch by Eli Schwartz. (Github issue #5504)

• The sdist was missing the Shadow.pyi stub file.

3.0.0 unified release notes

Cython 3.0.0 has been a very large effort that cleaned up many old warts, introduced many new features, and introduces a couple of intentional behaviour changes, even though the goal remained to stay compatible as much as possible with Cython 0.29.x. For details, see the migration guide.

As the development was spread out over several years, a lot of things have happened in the meantime. Many crucial bugfixes and some features were backported to 0.29.x and are not strictly speaking “new” in Cython 3.0.0.

Major themes in 3.0.0

Compatibility with CPython and the Python C API

Since Cython 3.0.0 started development, CPython 3.8-3.11 were released. All these are supported in Cython, including experimental support for the in-development CPython 3.12. On the other end of the spectrum, support for Python 2.6 was dropped.

Cython interacts very closely with the C-API of Python, which is where most of the adaptation work happens.

Related changes

• The long deprecated include files python_*, stdio, stdlib and stl in Cython/Includes/Deprecated/ were removed. Use the libc.* and cpython.* pxd modules instead. Patch by Jeroen Demeyer. (Github issue #2904)

• The Py_hash_t type failed to accept arbitrary “index” values. (Github issue #2752)

• @cython.trashcan(True) can be used on an extension type to enable the CPython Enabling the deallocation trashcan. This allows deallocating deeply recursive objects without overflowing the stack. Patch by Jeroen Demeyer. (Github issue #2842)

• PyEval_InitThreads() is no longer used in Py3.7+ where it is a no-op.

• A low-level inline function total_seconds(timedelta) was added to cpython.datetime to bypass the Python method call. Note that this function is not guaranteed to give exactly the same results for very large time intervals. Patch by Brock Mendel. (Github issue #3616)

• The internal CPython macro Py_ISSPACE() is no longer used. Original patch by Andrew Jones. (Github issue #4111)

• The value PyBUF_MAX_NDIM was added to the cpython.buffer module. Patch by John Kirkham. (Github issue #3811)

• A new module cpython.time was added with some low-level alternatives to Python’s time module. Patch by Brock Mendel. (Github issue #3767)

• More C-API declarations for cpython.datetime were added. Patch by Bluenix2. (Github issue #4128)

• C-API declarations for context variables in Python 3.7 were added. Original patch by Zolisa Bleki. (Github issue #2281)

• C-API declarations for cpython.fileobject were added. Patch by Zackery Spytz. (Github issue #3906)

• The signature of PyFloat_FromString() in cpython.float was changed to match the signature in Py3. It still has an automatic fallback for Py2. (Github issue #3909)

• PyMem_[Raw]Calloc() was added to the cpython.mem declarations. Note that the Raw versions are no longer #defined by Cython. The previous macros were not considered safe. Patch by William Schwartz and David Woods. (Github issue #3047)

• The runtime size check for imported PyVarObject types was improved to reduce false positives and adapt to Python 3.11. Patch by David Woods. (Github issues #4827, #4894)

• The generated C code failed to compile in CPython 3.11a4 and later. (Github issue #4500)

• pyximport no longer uses the deprecated imp module. Patch by Matúš Valo. (Github issue #4560)

• Improvements to PyTypeObject definitions in pxd wrapping of libpython. Patch by John Kirkham. (Github issue #4699)

• Some old usages of the deprecated Python imp module were replaced with importlib. Patch by Matúš Valo. (Github issue #4640)

• cpdef enums no longer use OrderedDict but dict in Python 3.6 and later. Patch by GalaxySnail. (Github issue #5180)

• Several problems with CPython 3.12 were resolved. (Github issue #5238)

• The exception handling code was adapted to CPython 3.12. (Github issue #5442)

• The Python int handling code was adapted to make use of the new PyLong internals in CPython 3.12. (Github issue #5353)

• A compile error when using __debug__ was resolved.

• The deprecated _PyGC_FINALIZED() C-API macro is no longer used. Patch by Thomas Caswell and Matúš Valo. (Github issue #5481)

• A crash in Python 2.7 was fixed when cleaning up extension type instances at program end.

Compatibility with other Python implementations

Cython tries to support other Python implementations, largely on a best-effort basis. The most advanced support exists for PyPy, which is tested in our CI and considered supported.

Related changes

• An unsupported C-API call in PyPy was fixed. Patch by Max Bachmann. (Github issue #4055)

• Support for the now unsupported Pyston V1 was removed in favour of Pyston V2. Patch by Marius Wachtler. (Github issue #4211)

• A C compiler warning in PyPy3 regarding PyEval_EvalCode() was resolved.

• Some compatibility issues with PyPy were resolved. Patches by Max Bachmann, Matti Picus. (Github issues #4454, #4477, #4478, #4509, #4517)

• An initial set of adaptations for GraalVM Python was implemented. Note that this does not imply any general support for this target or that your code will work at all in this environment. But testing should be possible now. Patch by David Woods. (Github issue #4328)

• A work-around for StacklessPython < 3.8 was disabled in Py3.8 and later. (Github issue #4329)

Initial support for Limited API

CPython provides a stable, limited subset of its C-API as the so-called Limited API. This C-API comes with the guarantee of a stable ABI, meaning that extensions modules that were compiled for one version of CPython can also be imported in later versions without recompilation.

There is initial support for this in Cython. By defining the CYTHON_LIMITED_API macro, Cython cuts down its C-API usage and tries to adhere to the Limited C-API, probably at the cost of a bit of performance. In order to get full benefit from the limited API you will also need to define the CPython macro Py_LIMITED_API to a specific CPython compatibility version, which additionally restricts the C-API during the C compilation, thus enforcing the forward compatibility of the extension module.

Note that “initial support” in Cython really means that setting the Py_LIMITED_API macro will almost certainly not yet work for your specific code. There are limitations in the Limited C-API that are difficult for Cython to generate C code for, so some advanced Python features (like async code) may not lead to C code that cannot adhere to the Limited C-API, or where Cython simply does not know yet how to adhere to it. Basically, if you get your code to compile with both macros set, and it passes your test suite, then it should be possible to import the extension module also in later CPython versions.

The experimental feature flags CYTHON_USE_MODULE_STATE and CYTHON_USE_TYPE_SPECS enable some individual aspects of the Limited API implementation independently.

Related changes

• Preliminary support for the CPython’s Py_LIMITED_API (stable ABI) is available by setting the CYTHON_LIMITED_API C macro. Note that the support is currently in an early stage and many features do not yet work. You currently still have to define Py_LIMITED_API externally in order to restrict the API usage. This will change when the feature stabilises. Patches by Eddie Elizondo and David Woods. (Github issues #3223, #3311, #3501)

• Limited API support was improved. Patches by Matthias Braun. (Github issues #3693, #3707)

• New C feature flags: CYTHON_USE_MODULE_STATE, CYTHON_USE_TYPE_SPECS Both are currently considered experimental. (Github issue #3611)

• _Py_TPFLAGS_HAVE_VECTORCALL was always set on extension types when using the limited API. Patch by David Woods. (Github issue #4453)

• Limited API C preprocessor warning is compatible with MSVC. Patch by Victor Molina Garcia. (Github issue #4826)

• The embedding code no longer calls deprecated C-API functions but uses the new PyConfig API instead on CPython versions that support it (3.8+). Patch by Alexander Shadchin. (Github issue #4895)

• Some C code issue were resolved for the Limited API target. (Github issues #5264, #5265, #5266)

• Conversion of Python ints to C int128 is now always supported, although slow if dedicated C-API support is missing (_PyLong_AsByteArray()), specifically in the Limited C-API. (Github issue #5419)

• Custom buffer slot methods are now supported in the Limited C-API of Python 3.9+. Patch by Lisandro Dalcin. (Github issue #5422)

Improved fidelity to Python semantics

Implemented PEPs

• PEP-3131: Supporting Non-ASCII Identifiers (Github issue #2601)

• PEP-479: generator_stop (enabled by default for language_level=3) (Github issue #2580)

• PEP-487: Simpler customisation of class creation (Github issue #2781)

• PEP-563: Postponed Evaluation of Annotations (Github issue #3285)

• PEP-570: Positional-Only Parameters (Github issue #2915)

• PEP-572: Assignment Expressions (a.k.a. the walrus operator :=) (Github issue #2636)

• PEP-590: Vectorcall protocol (Github issue #2263)

• PEP-614: Relaxing Grammar Restrictions On Decorators (Github issue #4570)

Typing support in the sense of PEP-484 (Github issues #3949, #4243) and PEP-560 (Github issues #2753, #3537, #3764) was also improved.

The default language level was changed to 3str, i.e. Python 3 semantics, but with str literals (also in Python 2.7). This is a backwards incompatible change from the previous default of Python 2 semantics. The previous behaviour is available through the directive language_level=2. (Github issue #2565). This covers changes such as using the print-function instead of the print-statement, and integer-integer division giving a floating point answer. Most of these changes were available in earlier versions of Cython but are now the default.

Cython 3.0.0 also aligns its own language semantics more closely with Python, in particular:

• the power operator has changed to give a result matching what Python does rather than keeping the same types as the input (as in C),

• operator overloading of cdef classes behaves much more like Python classes,

• Cython’s behaviour when using type annotations aligns more closely with their standard use in Python.

Related changes

• Cython no longer generates __qualname__ attributes for classes in Python 2.x since they are problematic there and not correctly maintained for subclasses. Patch by Jeroen Demeyer. (Github issue #2772)

• Binding staticmethods of Cython functions were not behaving like Python methods. Patch by Jeroen Demeyer. (Github issue #3106, #3102)

• Compiling package __init__ files could fail under Windows due to an undefined export symbol. (Github issue #2968)

• __init__.pyx files were not always considered as package indicators. (Github issue #2665)

• Setting language_level=2 in a file did not work if language_level=3 was enabled globally before. Patch by Jeroen Demeyer. (Github issue #2791)

• __doc__ was not available inside of the class body during class creation. (Github issue #1635)

• The first function line number of functions with decorators pointed to the signature line and not the first decorator line, as in Python. Patch by Felix Kohlgrüber. (Github issue #2536)

• Pickling unbound methods of Python classes failed. Patch by Pierre Glaser. (Github issue #2972)

• Item access (subscripting) with integer indices/keys always tried the Sequence protocol before the Mapping protocol, which diverged from Python semantics. It now passes through the Mapping protocol first when supported. (Github issue #1807)

• Nested dict literals in function call kwargs could incorrectly raise an error about duplicate keyword arguments, which are allowed when passing them from dict literals. (Github issue #2963)

• Diverging from the usual behaviour, len(memoryview), len(char*) and len(Py_UNICODE*) returned an unsigned size_t value. They now return a signed Py_ssize_t, like other usages of len().

• The unicode methods .upper(), .lower() and .title() were incorrectly optimised for single character input values and only returned the first character if multiple characters should have been returned. They now use the original Python methods again.

• The cython.view.array type supports inheritance. Patch by David Woods. (Github issue #3413)

• The builtin abs() function can now be used on C numbers in nogil code. Patch by Elliott Sales de Andrade. (Github issue #2748)

• The attributes gen.gi_frame and coro.cr_frame of Cython compiled generators and coroutines now return an actual frame object for introspection. (Github issue #2306)

• Inlined properties can be defined for external extension types. Patch by Matti Picus. (Github issue #2640, redone later in #3571)

• Unicode module names and imports are supported. Patch by David Woods. (Github issue #3119)

• __arg argument names in methods were not mangled with the class name. Patch by David Woods. (Github issue #1382)

• With language_level=3/3str, Python classes without explicit base class are now new-style (type) classes also in Py2. Previously, they were created as old-style (non-type) classes. (Github issue #3530)

• Conditional blocks in Python code that depend on cython.compiled are eliminated at an earlier stage, which gives more freedom in writing replacement Python code. Patch by David Woods. (Github issue #3507)

• Python private name mangling now falls back to unmangled names for non-Python globals, since double-underscore names are not uncommon in C. Unmangled Python names are also still found as a legacy fallback but produce a warning. Patch by David Woods. (Github issue #3548)

• The print statement (not the print() function) is allowed in nogil code without an explicit with gil section.

• repr() was assumed to return str instead of unicode with language_level=3. (Github issue #3736)

• Type inference now understands that a, *b = x assigns a list to b.

• No/single argument functions now accept keyword arguments by default in order to comply with Python semantics. The marginally faster calling conventions METH_NOARGS and METH_O that reject keyword arguments are still available with the directive @cython.always_allow_keywords(False). (Github issue #3090)

• Special methods for binary operators now follow Python semantics. Rather than e.g. a single __add__ method for cdef classes, where “self” can be either the first or second argument, one can now define both __add__ and __radd__ as for standard Python classes. This behavior can be disabled with the c_api_binop_methods directive to return to the previous semantics in Cython code (available from Cython 0.29.20), or the reversed method (__radd__) can be implemented in addition to an existing two-sided operator method (__add__) to get a backwards compatible implementation. (Github issue #2056)

• Generator expressions in pxd-overridden cdef functions could fail to compile. Patch by Matúš Valo. (Github issue #3477)

• Calls to .__class__() of a known extension type failed. Patch by David Woods. (Github issue #3954)

• Structs could not be instantiated with positional arguments in pure Python mode.

• Annotations were not exposed on annotated (data-)classes. Patch by matsjoyce. (Github issue #4151)

• Docstrings of cpdef enums are now copied to the enum class. Patch by matham. (Github issue #3805)

• asyncio.iscoroutinefunction() now recognises coroutine functions also when compiled by Cython. Patch by Pedro Marques da Luz. (Github issue #2273)

• Self-documenting f-strings (=) were implemented. Patch by davfsa. (Github issue #3796)

• cython.array supports simple, non-strided views. (Github issue #3775)

• Attribute annotations in Python classes are now ignored, because they are just Python objects in a dict (as opposed to the fields of extension types). Patch by David Woods. (Github issues #4196, #4198)

• A warning was added when __defaults__ or __kwdefaults__ of Cython compiled functions were re-assigned, since this does not current have an effect. Patch by David Woods. (Github issue #2650)

• The self argument of static methods in .pxd files was incorrectly typed. Patch by David Woods. (Github issue #3174)

• Default values for memory views arguments were not properly supported. Patch by Corentin Cadiou. (Github issue #4313)

• Python object types were not allowed as -> return type annotations. Patch by Matúš Valo. (Github issue #4433)

• The excess arguments in a for-in-range loop with more than 3 arguments to range() were silently ignored. Original patch by Max Bachmann. (Github issue #4550)

• Unsupported decorators on cdef functions were not rejected in recent releases. Patch by David Woods. (Github issue #4322)

• Fused functions were binding unnecessarily, which prevented them from being pickled. Patch by David Woods. (Github issue #4370)

• Decorators on inner functions were not evaluated in the right scope. Patch by David Woods. (Github issue #4367)

• Cython did not type the self argument in special binary methods. Patch by David Woods. (Github issue #4434)

• Circular imports of compiled modules could fail needlessly even when the import could already be resolved from sys.modules. Patch by Syam Gadde. (Github issue #4390)

• __del__(self) on extension types now maps to tp_finalize in Python 3. Original patch by ax487. (Github issue #3612)

• Reusing an extension type attribute name as a method name is now an error. Patch by 0dminnimda. (Github issue #4661)

• When using type annotations, func(x: list) or func(x: ExtType) (and other Python builtin or extension types) no longer allow None as input argument to x. This is consistent with the normal typing semantics in Python, and was a common gotcha for users who did not expect None to be allowed as input. To allow None, use typing.Optional as in func(x: Optional[list]). None is also automatically allowed when it is used as default argument, i.e. func(x: list = None). int and float are now also recognised in type annotations and restrict the value type at runtime. They were previously ignored. Note that, for backwards compatibility reasons, the new behaviour does not apply when using Cython’s C notation, as in func(list x). Here, None is still allowed, as always. Also, the annotation_typing directive can now be enabled and disabled more finely within the module. (Github issues #2696, #3883, #4606, #4669, #4886)

• The parser allowed some invalid spellings of .... Patch by 0dminnimda. (Github issue #4868)

• The __self__ attribute of fused functions reports its availability correctly with hasattr(). Patch by David Woods. (Github issue #4808)

• Several optimised string methods failed to accept None as arguments to their options. Test patch by Kirill Smelkov. (Github issue #4737)

• Cython generators and coroutines now identify as CO_ASYNC_GENERATOR, CO_COROUTINE and CO_GENERATOR accordingly. (Github issue #4902)

• Memory views and the internal Cython array type now identify as collections.abc.Sequence. Patch by David Woods. (Github issue #4817)

• Context managers can be written in parentheses. Patch by David Woods. (Github issue #4814)

• Some parser issues were resolved. (Github issue #4992)

• Unused **kwargs arguments did not show up in locals(). (Github issue #4899)

• Relative imports failed in compiled __init__.py package modules. Patch by Matúš Valo. (Github issue #3442)

• Extension types are now explicitly marked as immutable types to prevent them from being considered mutable. Patch by Max Bachmann. (Github issue #5023)

• int(Py_UCS4) returned the code point instead of the parsed digit value. (Github issue #5216)

• Calling bound classmethods of builtin types could fail trying to call the unbound method. (Github issue #5051)

• Generator expressions and comprehensions now look up their outer-most iterable on creation, as Python does, and not later on start, as they did previously. (Github issue #1159)

• Bound C methods can now coerce to Python objects. (Github issues #4890, #5062)

• cpdef enums can now be pickled. (Github issue #5120)

• The Python Enum of a cpdef enum now inherits from IntFlag to better match both Python and C semantics of enums. (Github issue #2732)

• The special __*pow__ methods now support the 2- and 3-argument variants. (Github issue #5160)

• The ** power operator now behaves more like in Python by returning the correct complex result if required by math. A new cpow directive was added to turn on the previous C-like behaviour. (Github issue #4936)

• With language_level=2, imports of modules in packages could return the wrong module in Python 3. (Github issue #5308)

• Function signatures containing a type like tuple[()] could not be printed. Patch by Lisandro Dalcin. (Github issue #5355)

• __qualname__ and __module__ were not available inside of class bodies. (Github issue #4447)

• A new directive embedsignature.format was added to select the format of the docstring embedded signatures between python, c and argument clinic. Patch by Lisandro Dalcin. (Github issue #5415)

• ctuples can now be assigned from arbitrary sequences, not just Python tuples.

Improvements in Pure Python mode

Cython strives to be able to parse newer Python constructs for use with its pure python mode, which has been a focus. In short, this allows to compile a wider range of Python code into optimized C code.

Pure python mode gained many new features and was generally overhauled to make it as capable as the Cython syntax. Except for using external C/C++ libraries, it should now be possible to express all Cython code and use all features in regular Python syntax. The very few remaining exceptions or bugs are noted in the documentation.

Additionally, the documentation has been substantially updated (primarily by Matúš Valo and 0dminnimda) to show both the older Cython syntax and pure Python syntax.

Related changes

• The cython.declare() and cython.cast() functions could fail in pure mode. Patch by Dmitry Shesterkin. (Github issue #3244)

• Fused argument types were not correctly handled in type annotations and cython.locals(). Patch by David Woods. (Github issues #3391, #3142)

• nogil functions now avoid acquiring the GIL on function exit if possible even if they contain with gil blocks. (Github issue #3554)

• The @returns() decorator propagates exceptions by default for suitable C return types when no @exceptval() is defined. (Github issues #3625, #3664)

• Extension types inheriting from Python classes could not safely be exposed in .pxd files. (Github issue #4106)

• Default arguments of methods were not exposed for introspection. Patch by Vladimir Matveev. (Github issue #4061)

• Literal list assignments to pointer variables declared in PEP-526 notation failed to compile.

• The type cython.Py_hash_t is available in Python mode.

• A cimport is now supported in pure Python code by prefixing the imported module name with cython.cimports., e.g. from cython.cimports.libc.math import sin. (GIthub issue #4190)

• Directives starting with optimization.* in pure Python mode were incorrectly named. It should have been optimize.*. Patch by David Woods. (Github issue #4258)

• Invalid and misspelled cython.* module names were not reported as errors. (Github issue #4947)

• The annotation_typing directive was missing in pure Python mode. Patch by 0dminnimda. (Github issue #5194)

• Memoryviews with object item type were not supported in Python type declarations. (Github issue #4907)

• Subscripted builtin types in type declarations (like list[float]) are now better supported. (Github issue #5058)

• Unknown type annotations (e.g. because of typos) now emit a warning at compile time. Patch by Matúš Valo. (Github issue #5070)

• typing.Optional could fail on tuple types. (Github issue #5263)

• from cython cimport … as … could lead to imported names not being found in annotations. Patch by Chia-Hsiang Cheng. (Github issue #5235)

• Simple tuple types like (int, int) are no longer accepted in Python annotations and require the Python notation instead (e.g. tuple[cython.int, cython.int]). (Github issue #5397)

• The Python implementation of cimport cython.cimports… could raise an ImportError instead of an AttributeError when looking up package variable names. Patch by Matti Picus. (Github issue #5411)

• A new decorator @cython.with_gil is available in Python code to match the with gil function declaration in Cython syntax.

• with gil and with nogil(flag) now accept their flag argument also in Python code. Patch by Matúš Valo. (Github issue #5113)

Code generation changes

Cython has gained several major new features that speed up both the development and the code. Dataclasses have gained an extension type equivalent that implements the dataclass features in C code. Similarly, the @functools.total_ordering decorator to an extension type will implement the comparison functions in C.

Finally, NumPy ufuncs can be generated from simple computation functions with the new @cython.ufunc decorator.

Related changes

• with gil/nogil statements can be conditional based on compile-time constants, e.g. fused type checks. Patch by Noam Hershtig. (Github issue #2579)

• The names of Cython’s internal types (functions, generator, coroutine, etc.) are now qualified with the module name of the internal Cython module that is used for sharing them across Cython implemented modules, for example _cython_3_0a5.coroutine. This was done to avoid making them look like homeless builtins, to help with debugging, and in order to avoid a CPython warning according to https://bugs.python.org/issue20204

• A @cython.total_ordering decorator has been added to automatically implement all comparison operators, similar to functools.total_ordering. Patch by Spencer Brown. (Github issue #2090)

• A new decorator @cython.dataclasses.dataclass was implemented that provides compile time dataclass generation capabilities to cdef classes (extension types). Patch by David Woods. (Github issue #2903). kw_only dataclasses added by Yury Sokov. (Github issue #4794)

• A new function decorator @cython.ufunc automatically generates a (NumPy) ufunc that applies the calculation function to an entire memoryview. (Github issue #4758)

• Generated NumPy ufuncs could crash for large arrays due to incorrect GIL handling. (Github issue #5328)

• Some invalid directive usages are now detected and rejected, e.g. using @ccall together with @cfunc, and applying @cfunc to a @ufunc. Cython also warns now when a directive is applied needlessly. (Github issue #5399 et al.)

• The normal @dataclasses.dataclass and @functools.total_ordering decorators can now be used on extension types. Using the corresponding @cython.* decorator will automatically turn a Python class into an extension type (no need for @cclass). (Github issue #5292)

Interaction with numpy

The NumPy declarations (cimport numpy) were moved over to the NumPy project in order to allow version specific changes on their side.

One effect is that Cython does not use deprecated NumPy C-APIs any more. Thus, you can define the respective NumPy C macro to get rid of the compatibility warning at C compile time.

Related changes

• cython.inline() now sets the NPY_NO_DEPRECATED_API=NPY_1_7_API_VERSION C macro automatically when numpy is imported in the code, to avoid C compiler warnings about deprecated NumPy C-API usage.

• Deprecated NumPy API usages were removed from numpy.pxd. Patch by Matti Picus. (Github issue #3365)

• numpy.import_array() is automatically called if numpy has been cimported and it has not been called in the module code. This is intended as a hidden fail-safe so user code should continue to call numpy.import_array. Patch by David Woods. (Github issue #3524)

• The outdated getbuffer/releasebuffer implementations in the NumPy declarations were removed so that buffers declared as ndarray now use the normal implementation in NumPy.

• Several macros/functions declared in the NumPy API are now usable without holding the GIL.

• The numpy declarations were updated. Patch by Brock Mendel. (Github issue #3630)

• ndarray.shape failed to compile with Pythran and recent NumPy. Patch by Serge Guelton. (Github issue #3762)

• A C-level compatibility issue with recent NumPy versions was resolved. Patch by David Woods. (Github issue #4396)

• The generated modules no longer import NumPy internally when using fused types but no memoryviews. Patch by David Woods. (Github issue #4935)

• np.long_t and np.ulong_t were removed from the NumPy declarations, syncing Cython with upstream NumPy v1.25.0. The aliases were confusing since they could mean different things on different platforms.

Exception handling

Cython-implemented C functions now propagate exceptions by default, rather than swallowing them in non-object returning function if the user forgot to add an except declaration to the signature. This was a long-standing source of bugs, but can require adding the noexcept declaration to existing functions if exception propagation is really undesired. (Github issue #4280)

To ease the transition for this break in behaviour, it is possible to set legacy_implicit_noexcept=True.

Related changes

• The assert statement is allowed in nogil sections. Here, the GIL is only acquired if the AssertionError is really raised, which means that the evaluation of the asserted condition only allows C expressions.

• The exception handling annotation except +* was broken. Patch by David Woods. (Github issues #3065, #3066)

• Improve conversion between function pointers with non-identical but compatible exception specifications. Patches by David Woods. (Github issues #4770, #4689)

• Exceptions within for-loops that run over memoryviews could lead to a ref-counting error. Patch by David Woods. (Github issue #4662)

• To opt out of the new, safer exception handling behaviour, legacy code can set the new directive legacy_implicit_noexcept=True for a transition period to keep the previous, unsafe behaviour. This directive will eventually be removed in a later release. Patch by Matúš Valo. (Github issue #5094)

• Cython implemented C functions now propagate exceptions by default, rather than swallowing them in non-object returning function if the user forgot to add an except declaration to the signature. This was a long-standing source of bugs, but can require adding the noexcept declaration to existing functions if exception propagation is really undesired. (Github issue #4280)

• The code except +nogil (declaring a C++ exception handler function called nogil) is now rejected because it is almost certainly a typo from except + nogil. (Github issue #5430)

• Handling freshly raised exceptions that didn’t have a traceback yet could crash. (Github issue #5495)

Optimizations

Generating efficient code has long been a goal of Cython, and 3.0 continues that. Probably the most significant change is that Cython functions use the PEP-590 vectorcall protocol on Python 3.7 and higher.

Related changes

• Name lookups in class bodies no longer go through an attribute lookup. Patch by Jeroen Demeyer. (Github issue #3100)

• Extension types that do not need their own tp_new implementation (because they have no object attributes etc.) directly inherit the implementation of their parent type if possible. (Github issue #1555)

• Some list copying is avoided internally when a new list needs to be created but we already have a fresh one. (Github issue #3494)

• Multiplication of Python numbers with small constant integers is faster. (Github issue #2808)

• String concatenation can now happen in place if possible, by extending the existing string rather than always creating a new one. Patch by David Woods. (Github issue #3453)

• The str() builtin now calls PyObject_Str() instead of going through a Python call. Patch by William Ayd. (Github issue #3279)

• Reimports of already imported modules are substantially faster. (Github issue #2854)

• The dispatch to fused functions is now linear in the number of arguments, which makes it much faster, often 2x or more, and several times faster for larger fused types with many specialisations. Patch by will-ca. (Github issue #1385)

• The fastcall/vectorcall protocols are used for several internal Python calls. (Github issue #3540)

• nogil functions now avoid acquiring the GIL on function exit if possible even if they contain with gil blocks. (Github issue #3554)

• Type inference now works for memory views and slices. Patch by David Woods. (Github issue #2227)

• For-in-loop iteration over bytearray and memory views is optimised. Patch by David Woods. (Github issue #2227)

• For-in-loop iteration over bytearray and memory views is optimised. Patch by David Woods. (Github issue #2227)

• float(…) is optimised for string arguments (str/bytes/bytearray).

• [...] * N is optimised for C integer multipliers N. (Github issue #3922)

• Some constant tuples containing strings were not deduplicated. Patch by David Woods. (Github issue #4353)

• Memory views can use atomic CPU instructions instead of locks in more cases. Patch by Sam Gross. (Github issue #4912)

• Cython avoids raising StopIteration in __next__ methods when possible. Patch by David Woods. (Github issue #3447)

• Larger numbers of extension types with multiple subclasses could take very long to compile. Patch by Scott Wolchok. (Github issue #5139)

• Integer comparisons avoid Python coercions if possible. (Github issue #4821)

• The call-time dispatch for fused memoryview types is less slow. (Github issue #5073)

• Python’s memoryview is now a known builtin type with optimised properties. (Github issue #3798)

• Multiplying a sequence by a C integer avoids creating and intermediate Python integer.

• The reference counting of memory views involved useless overhead. (Github issue #5510)

Compatibility with C

The support for C features like const or volatile was substantially improved.

The generated code has been cleared up to reduce the number of C compiler warnings emitted.

Related changes

• A C compiler cast warning was resolved. Patch by Michael Buesch. (Github issue #2775)

• Constant integer expressions that used a negative exponent were evaluated as integer 0 instead of the expected float value. Patch by Kryštof Pilnáček. (Github issue #2133)

• Several declarations in cpython.*, libc.* and libcpp.* were added. Patches by Jeroen Demeyer, Matthew Edwards, Chris Gyurgyik, Jerome Kieffer and Zackery Spytz. (Github issues #3468, #3332, #3202, #3188, #3179, #2891, #2826, #2713)

• The volatile C modifier is supported in Cython code. Patch by Jeroen Demeyer. (Github issue #1667)

• const can be used together with fused types. Patch by Thomas Vincent. (Github issue #1772)

• Temporary buffer indexing variables were not released and could show up in C compiler warnings, e.g. in generators. Patch by David Woods. (Github issues #3430, #3522)

• The C property feature has been rewritten and now requires C property methods to be declared inline (#3571).

• Cython generates C compiler branch hints for unlikely user defined if-clauses in more cases, when they end up raising exceptions unconditionally. This now includes exceptions being raised in nogil/with gil sections.

• Several issues with arithmetic overflow handling were resolved, including undefined behaviour in C. Patch by Sam Sneddon. (Github issue #3588)

• libc.math was extended to include all C99 function declarations. Patch by Dean Scarff. (Github issue #3570)

• Some C compiler warninge were resolved. Patches by Max Bachmann. (Github issue #4053, #4059, #4054, #4148, #4162)

• A C compiler warning about enum value casting was resolved in GCC. (Github issue #2749)

• A C compiler warning about unused code was resolved. (Github issue #3763)

• Some compiler problems and warnings were resolved. Patches by David Woods, 0dminnimda, Nicolas Pauss and others. (Github issues #4317, #4324, #4361, #4357)

• Some C compiler warnings were fixed. Patch by mwtian. (Github issue #4831)

• A case of undefined C behaviour was resolved in the list slicing code. Patch by Richard Barnes. (Github issue #4734)

• Typedefs for the bint type did not always behave like bint. Patch by Nathan Manville and 0dminnimda. (Github issue #4660)

• Intel C compilers could complain about unsupported gcc pragmas. Patch by Ralf Gommers. (Github issue #5052)

• Structs that contained an array field resulted in incorrect C code. Their initialisation now uses memcpy(). Patch by Chia-Hsiang Cheng. (Github issue #5178)

• The module state struct was not initialised in correct C (before C23), leading to compile errors on Windows. Patch by yudonglin. (Github issue #5169)

• cdef public functions declared in .pxd files could use an incorrectly mangled C name. Patch by EpigeneMax. (Github issue #2940)

• const types could not be returned from functions. Patch by Mike Graham. (Github issue #5135)

• C11 complex.h is now properly detected. (Github issue #2513)

• Standard C/C++ atomic operations are now used for memory views, if available. (Github issue #4925)

• C arrays can be initialised inside of nogil functions. Patch by Matúš Valo. (Github issue #1662)

• Very long Python integer constants could exceed the maximum C name length of MSVC. Patch by 0dminnimda. (Github issue #5290)

• Some C compiler warnings were resolved. Patches by Matt Tyson, Lisandro Dalcin, Philipp Wagner, Matti Picus et al. (Github issues #5417, #5418, #5421, #5437, #5438, #5443)

• Some typedef declarations for libc function types were fixed. (Github issue #5498)

• With MSVC, Cython no longer enables C-Complex support by accident (which is not supported there). (Github issue #5512)

Compatibility with C++

Many C++ features like forwarding references or std::move are now supported or even used internally, if possible.

Cython’s wrapping of the C++ standard library has been extended.

A new cpp_locals` directive enables C++ local variables to initialized when assigned to rather than at the start of the function, making them behave more like Python variables, and also removing the requirement for them to be default constructible.

Related changes

• C++ typeid() failed for fused types. Patch by David Woods. (Github issue #3203)

• std::move() is now used in C++ mode for internal temp variables to make them work without copying values. Patch by David Woods. (Github issues #3253, #1612)

• The C++ typeid() function was allowed in C mode. Patch by Celelibi. (Github issue #3637)

• C++ references failed to compile when used as Python object indexes. Patch by David Woods. (Github issue #3754)

• The construct for x in cpp_function_call() failed to compile. Patch by David Woods. (Github issue #3663)

• Some C++ STL methods did not propagate exceptions. Patch by Max Bachmann. (Github issue #4079)

• A compile failure for C++ enums in Py3.4 / MSVC was resolved. Patch by Ashwin Srinath. (Github issue #3782)

• Cython compiled functions always provided a __self__ attribute, regardless of being used as a method or not. Patch by David Woods. (Github issue #4036)

• Overloaded C++ static methods were lost. Patch by Ashwin Srinath. (Github #1851)

• Nested C++ types were not usable through ctypedefs. Patch by Vadim Pushtaev. (Github issue #4039)

• More declarations for C++ string methods were added.

• Converting C++ containers to Python lists uses less memory allocations. Patch by Max Bachmann. (Github issue #4081)

• std::move() is now also called for temps during yield. Patch by Yu Feng. (Github issue #4154)

• The destructor is now called for fields in C++ structs. Patch by David Woods. (Github issue #3226)

• Conversion from Python dicts to std::map was broken. Patch by David Woods and Mikkel Skofelt. (Github issues #4228, #4231)

• Code optimisations were not applied to methods of Cython implemented C++ classes. Patch by David Woods. (Github issue #4212)

• C++17 execution policies are supported in libcpp.algorithm. Patch by Ashwin Srinath. (Github issue #3790)

• A new directive cpp_locals was added that allows local C++ variables to be lazily initialised (without default constructor), thus making them behave more like Python variables. Patch by David Woods. (Github issue #4160)

• Generated utility code for C++ conversions no longer depends on several user definable directives that may make it behave incorrectly. Patch by David Woods. (Github issue #4206)

• Several issues with the new cpp_locals directive were resolved and its test coverage improved. Patch by David Woods. (Github issues #4265, #4266)

• Declarations for libcpp.algorithms, libcpp.set and libcpp.unordered_set were extended. Patch by David Woods. (Github issues #4271, #4273)

• Several C++ library declarations were added and fixed. Patches by Dobatymo, account-login, Jonathan Helgert, Evgeny Yakimov, GalaxySnail, Max Bachmann. (Github issues #4408, #4419, #4410, #4395, #4423, #4448, #4462, #3293, #4522, #2171, #4531)

• Templating C++ classes with memory view types lead to buggy code and is now rejected. Patch by David Woods. (Github issue #3085)

• prange loops generated incorrect code when cpp_locals is enabled. Patch by David Woods. (Github issue #4354)

• Direct assignments to C++ references are now allowed. Patch by David Woods. (Github issue #1863)

• Conversion from Python dict to C++ map now supports arbitrary Python mappings, not just dicts.

• Some C++ and CPython library declarations were extended and fixed. Patches by Max Bachmann, Till Hoffmann, Julien Jerphanion, Wenjun Si. (Github issues #4530, #4528, #4710, #4746, #4751, #4818, #4762, #4910)

• Some C/C++ warnings were resolved. Patches by Max Bachmann, Alexander Shadchin, at al. (Github issues #5004, #5005, #5019, #5029, #5096)

• C++ references did not work on fused types. (Github issue #4717)

• C++ iteration more safely stores the iterable in temporary variables. Patch by Xavier. (Github issue #3828)

• C++ post-increment/-decrement operators were not correctly looked up on declared C++ classes, thus allowing Cython declarations to be missing for them and incorrect C++ code to be generated. Patch by Max Bachmann. (Github issue #4536)

• cdef public functions used an incorrect linkage declaration in C++. Patch by Maximilien Colange. (Github issue #1839)

• Declarations were added for the C++ bit operations, some other parts of C++20 and CPython APIs. Patches by Jonathan Helgert, Dobatymo, William Ayd and Max Bachmann. (Github issues #4962, #5101, #5157, #5163, #5257)

• cpp_locals no longer have to be “assignable”. (Github issue #4558)

• Nested cppclass definitions are supported. Patch by samaingw. (Github issue #1218)

• reversed() can now be used together with C++ iteration. Patch by Chia-Hsiang Cheng. (Github issue #5002)

• Some C++ warnings regarding const usage in internally generated utility code were resolved. Patch by Max Bachmann. (Github issue #5301)

• Cython generated C++ code accidentally used C++11 features in some cases. (Github issue #5316)

• Fully qualified C++ names prefixed by a cimported module name could fail to compile. Patch by Chia-Hsiang Cheng. (Github issue #5229)

• C++ declarations for <cmath>, <numbers> and std::any were added. Patches by Jonathan Helgert and Maximilien Colange. (Github issues #5262, #5309, #5314)

• The extern "C" and extern "C++" markers that Cython generates for public functions can now be controlled by setting the C macro CYTHON_EXTERN_C.

• C++ containers of item type bint could conflict with those of item type int. (Github issue #5516)

• Reverse iteration in C++ no longer removes the const qualifier from the item type. Patch by Isuru Fernando. (Github issue #5478)

Commandline Interface

A number of new options were added to the cython and cythonize commands.

Related changes

• The command line parser was rewritten and modernised using argparse. Patch by Egor Dranischnikow. (Github issue #2952, #3001)

• cygdb gives better error messages when it fails to initialise the Python runtime support in gdb. Patch by Volker Weissmann. (Github issue #3489)

• --no-docstrings option added to cythonize script. Original patch by mo-han. (Github issue #2889)

• Code annotation accepts a new debugging argument --annotate-fullc that will include the complete syntax highlighted C file in the HTML output. (Github issue #2855)

• cygdb has a new option --skip-interpreter that allows using a different Python runtime than the one used to generate the debugging information. Patch by Alessandro Molina. (Github issue #4186)

• cythonize() and the corresponding CLI command now regenerate the output files also when they already exist but were generated by a different Cython version.

• The cython and cythonize commands ignored non-existing input files without error. Patch by Matúš Valo. (Github issue #4629)

• cythonize --help now also prints information about the supported environment variables. Patch by Matúš Valo. (Github issue #1711)

• Using the --working option could lead to sources not being found. Patch by Lisandro Dalcin. (Github issue #5365)

• Passing a language level and directives on the command line lost the language level setting. Patch by Matúš Valo. (Github issue #5484)

• cython --version now prints the version to both stdout and stderr (unless that is a TTY). (Github issue #5504)

Build integration

Cython has made a number of improvements both to how it compiles itself and how it integrates with external build tools. Most notably Cython has been moving to use setuptools instead of the deprecated/removed distutils where possible.

The new --depfile option generates dependency files to help integrate Cython with other build tools.

Related changes

• Binary Linux wheels now follow the manylinux2010 standard. Patch by Alexey Stepanov. (Github issue #3355)

• The search order for include files was changed. Previously it was include_directories, Cython/Includes, sys.path. Now it is include_directories, sys.path, Cython/Includes. This was done to allow third-party *.pxd files to override the ones in Cython. Patch by Matti Picus. (Github issue #2905)

• Source file fingerprinting now uses SHA-1 instead of MD5 since the latter tends to be slower and less widely supported these days. (Github issue #2790)

• The Cython AST code serialiser class CodeWriter in Cython.CodeWriter supports more syntax nodes.

• Parallel builds of Cython itself (setup.py build_ext -j N) failed on Windows.

• When importing the old Cython build_ext integration with distutils, the additional command line arguments leaked into the regular command. Patch by Kamekameha. (Github issue #2209)

• .pxd files can now be versioned by adding an extension like “.cython-30.pxd” to prevent older Cython versions (than 3.0 in this case) from picking them up. (Github issue #3577)

• The Cython CodeWriter can now handle more syntax constructs. Patch by Tao He. (Github issue #3514)

• The Cython CodeWriter mishandled no-argument return statements. Patch by Tao He. (Github issue #3795)

• Cython now detects when existing output files were not previously generated by itself and refuses to overwrite them. It is a common mistake to name the module file of a wrapper after the library (source file) that it wraps, which can lead to surprising errors when the file gets overwritten.

• The Cython.Build.BuildExecutable tool no longer executes the program automatically. Use cythonrun for that.

• Python modules were not automatically recompiled when only their .pxd file changed. Patch by Golden Rockefeller. (Github issue #1428)

• An unnecessary slow-down at import time was removed from Cython.Distutils. Original patch by Anthony Sottile. (Github issue #4224)

• A compiler crash when running Cython thread-parallel from distutils was resolved. (Github issue #4503)

• An incompatibility with recent coverage.py versions was resolved. Patch by David Woods. (Github issue #4440)

• pyximport now uses cythonize() internally. Patch by Matúš Valo. (Github issue #2304)

• Cython.Distutils.build_ext now uses cythonize() internally (previously known as new_build_ext), while still supporting the options that were available in the old implementation (old_build_ext). Patch by Matúš Valo. (Github issue #3541)

• Improve compatibility between classes pickled in Cython 3.0 and 0.29.x by accepting MD5, SHA-1 and SHA-256 checksums. (Github issue #4680)

• pyximport failed for long filenames on Windows. Patch by Matti Picus. (Github issue #4630)

• A new Cython build option --cython-compile-minimal was added to compile only a smaller set of Cython’s own modules, which can be used to reduce the package and install size.

• The environment variable CYTHON_FORCE_REGEN=1 can be used to force cythonize to regenerate the output files regardless of modification times and changes.

• The cythonize and cython commands have a new option -M / --depfile to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. The cythonize option was already available in Cython 0.29.27 (2022-01-28). Patches by Evgeni Burovski and Eli Schwartz. (Github issue #1214)

• Wheels now include a compiled parser again, which increases their size a little but gives about a 10% speed-up when running Cython.

• The wheel building process was migrated to use the cibuildwheel tool. Patch by Thomas Li. (Github issue #4736)

• setup.cfg was missing from the source distribution. (Github issue #5199)

• Extended glob paths with /**/ and \**\ for finding source files failed on Windows.

• Coverage analysis failed in projects with a separate source subdirectory. Patch by Sviatoslav Sydorenko and Ruben Vorderman. (Github issue #3636)

• Cython could crash when finding import files with dots in their names. Patch by Matúš Valo. (Github issue #5396)

• A module loading problem with cython.inline() on Windows was resolved.

Deprecations

Some older features of Cython have been deprecated. Most notable are the compile time DEF and IF statements, although we emphasise that they will remain until a good alternative exists for all their use-cases.

Related changes

• Dotted filenames for qualified module names (pkg.mod.pyx) are deprecated. Use the normal Python package directory layout instead. (Github issue #2686)

• “Declaration after use” is now an error for variables. Patch by David Woods. (Github issue #3976)

• Variables can no longer be declared with cpdef. Patch by David Woods. (Github issue #887)

• The compile-time DEF and IF statements are deprecated and generate a warning. They should be replaced with normal constants, code generation or C macros. (Github issue #4310)

• C-style array declarations (cdef int a[4]) are now (silently) deprecated in favour of the Java-style cdef int[4] a form. The latter was always available and the Python type declaration syntax already used it exclusively (a: int[4]). Patch by Matúš Valo. (Github issue #5248)

• The undocumented, untested and apparently useless syntax from somemodule cimport class/struct/union somename was removed. The type modifier is not needed here and a plain cimport of the name will do. (Github issue #4904)

Editor support

Related changes

• C compiler warnings and errors are now shown in Jupyter notebooks. Patch by Egor Dranischnikow. (Github issue #3751)

• An endless loop in cython-mode.el was resolved. Patch by Johannes Mueller. (Github issue #3218)

• The Emacs Cython mode file cython-mode.el is now maintained in a separate repo: https://github.com/cython/emacs-cython-mode

• The C code shown in the annotated HTML output could lack the last C code line(s).

Other changes

• Memoryviews failed to compile when the cache_builtins feature was disabled. Patch by David Woods. (Github issue #3406)

• Broadcast assignments to a multi-dimensional memory view slice could end up in the wrong places when the underlying memory view is known to be contiguous but the slice is not. (Github issue #2941)

• The Pythran shape attribute is supported. Patch by Serge Guelton. (Github issue #3307)

• --no-capture added to runtests.py to prevent stdout/stderr capturing during srctree tests. Patch by Matti Picus. (Github issue #2701)

• Decoding an empty bytes/char* slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3534)

• Creating an empty unicode slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3531)

• Complex buffer item types of structs of arrays could fail to validate. Patch by Leo and smutch. (Github issue #1407)

• Error handling in cython.array creation was improved to avoid calling C-API functions with an error held.

• Error handling early in the module init code could lead to a crash.

• Exception position reporting could run into race conditions on threaded code. It now uses function-local variables again.

• A reference leak on import failures was resolved. Patch by Max Bachmann. (Github issue #4056)

• Casting to ctuples is now allowed. Patch by David Woods. (Github issue #3808)

• Some issues were resolved that could lead to duplicated C names. Patch by David Woods. (Github issue #3716, #3741, #3734)

• Inline functions and other code in .pxd files could accidentally inherit the compiler directives of the .pyx file that imported them. Patch by David Woods. (Github issue #1071)

• Parts of the documentation were (and are being) rewritten to show the Cython language syntax next to the equivalent Python syntax. Patches by 0dminnimda and Matúš Valo. (Github issue #4187)

• A name collision when including multiple generated API header files was resolved. Patch by David Woods. (Github issue #4308)

• Very early errors during module initialisation could lead to crashes. Patch by David Woods. (Github issue #4377)

• Type errors when passing memory view arguments could leak buffer references. Patch by David Woods. (Github issue #4296)

• The GIL can now safely be released inside of nogil functions (which may actually be called with the GIL held at runtime). Patch by David Woods. (Github issue #4137)

• The return type of a fused function is no longer ignored for function pointers, since it is relevant when passing them e.g. as argument into other fused functions. Patch by David Woods. (Github issue #4644)

• Using memoryview arguments in closures of inner functions could lead to ref-counting errors. Patch by David Woods. (Github issue #4798)

• Decorators like @cfunc and @ccall could leak into nested functions and classes. Patch by David Woods. (Github issue #4092)

• Cython now uses a .dev0 version suffix for unreleased source installations.

• The Tempita module no longer contains HTML processing capabilities, which were found to be broken in Python 3.8 and later. Patch by Marcel Stimberg. (Github issue #3309)

• Nesting fused types in other fused types could fail to specialise the inner type. (Github issue #4725)

• Iterating over memoryviews in generator expressions could leak a buffer reference. (Github issue #4968)

• The C float type was not inferred on assignments. (Github issue #5234)

• Type checks for Python’s memoryview type generated incorrect C code. (Github issues #5268, #5270)

• Auto-generated utility code didn’t always have all required user defined types available. (Github issue #5269)

• cimport_from_pyx could miss some declarations. Patch by Chia-Hsiang Cheng. (Github issue #5318)

• For-loops now release the internal reference to their list/tuple iterable before instead of after the else: clause. This probably has no practical impact. (Github issue #5347)

• Extension type hierarchies were generated in the wrong order, thus leading to compile issues. Patch by Lisandro Dalcin. (Github issue #5395)

• The FAQ page was moved from the GitHub Wiki to the regular documentation to make it more visible.

3.0.0 (2023-07-17)

Bugs fixed

• A crash in Python 2.7 was fixed when cleaning up extension type instances at program end.

3.0.0 rc 2 (2023-07-13)

Bugs fixed

• Parser crash on hex/oct enum values. (Github issue #5524)

• cython --version now prints the version to both stdout and stderr (unless that is a TTY). (Github issue #5504)

3.0.0 rc 1 (2023-07-12)

Features added

• with gil and with nogil(flag) now accept their flag argument also in Python code. Patch by Matúš Valo. (Github issue #5113)

• A new decorator @cython.with_gil is available in Python code to match the with gil function declaration in Cython syntax.

• Assigning a list to a ctuple is slightly faster.

Bugs fixed

• The reference counting of memory views involved useless overhead. (Github issue #5510)

• Duplicate values in a cpdef enum could lead to invalid switch statements. (Github issue #5400)

• Handling freshly raised exceptions that didn’t have a traceback yet could crash. (Github issue #5495)

• Reverse iteration in C++ no longer removes the const qualifier from the item type. Patch by Isuru Fernando. (Github issue #5478)

• C++ containers of item type bint could conflict with those of item type int. (Github issue #5516)

• With MSVC, Cython no longer enables C-Complex support by accident (which is not supported there). (Github issue #5512)

• The Python implementation of cimport cython.cimports… could raise an ImportError instead of an AttributeError when looking up package variable names. Patch by Matti Picus. (Github issue #5411)

• Passing a language level and directives on the command line lost the language level setting. Patch by Matúš Valo. (Github issue #5484)

• Some typedef declarations for libc function types were fixed. (Github issue #5498)

• Some C compiler warnings and errors in CPython 3.12 were resolved.

• The deprecated _PyGC_FINALIZED() C-API macro is no longer used. Patch by Thomas Caswell and Matúš Valo. (Github issue #5481)

• A compile error when using __debug__ was resolved.

• A module loading problem with cython.inline() on Windows was resolved.

• cython --version now prints the version to stdout instead of stderr. (Github issue #5504)

• Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.36 (2023-07-04) release.

Other changes

• The FAQ page was moved from the GitHub Wiki to the regular documentation to make it more visible.

• np.long_t and np.ulong_t were removed from the NumPy declarations, syncing Cython with upstream NumPy v1.25.0. The aliases were confusing since they could mean different things on different platforms.

3.0.0 beta 3 (2023-05-24)

Features added

• Custom buffer slot methods are now supported in the Limited C-API of Python 3.9+. Patch by Lisandro Dalcin. (Github issue #5422)

• The extern "C" and extern "C++" markers that Cython generates for public functions can now be controlled by setting the C macro CYTHON_EXTERN_C.

• The Python int handling code was adapted to make use of the new PyLong internals in CPython 3.12. (Github issue #5353)

• Conversion of Python ints to C int128 is now always supported, although slow if dedicated C-API support is missing (_PyLong_AsByteArray()), specifically in the Limited C-API. (Github issue #5419)

• The exception handling code was adapted to CPython 3.12. (Github issue #5442)

• The dataclass implementation was adapted to support Python 3.12. (Github issue #5346)

• The normal @dataclasses.dataclass and @functools.total_ordering decorators can now be used on extension types. Using the corresponding @cython.* decorator will automatically turn a Python class into an extension type (no need for @cclass). (Github issue #5292)

• Multiplying a sequence by a C integer avoids creating and intermediate Python integer.

• ctuples can now be assigned from arbitrary sequences, not just Python tuples.

• A new directive embedsignature.format was added to select the format of the docstring embedded signatures between python, c and argument clinic. Patch by Lisandro Dalcin. (Github issue #5415)

• Some invalid directive usages are now detected and rejected, e.g. using @ccall together with @cfunc, and applying @cfunc to a @ufunc. Cython also warns now when a directive is applied needlessly. (Github issue #5399 et al.)

• Unicode identifier names now allow all letters defined in CPython 3.12.

Bugs fixed

• Some C compile failures in CPython 3.12.0a6/a7 were resolved.

• Cascaded comparisons between integer constants and Python types could fail to compile. (Github issue #5354)

• The internal macro __PYX_IS_UNSIGNED was accidentally duplicated in beta 2 which lead to C compile errors. Patch by 0dminnimda. (Github issue #5356)

• Memoryviews with typedef item types could fail to match the non-typedef item types. Patch by Yue Yang. (Github issue #5373)

• Fused memory views could raise a TypeError instead of a ValueError on creation. Patch by Matúš Valo. (Github issue #5401)

• Cython could crash when finding import files with dots in their names. Patch by Matúš Valo. (Github issue #5396)

• Selecting a context manager in parentheses and then calling it directly failed to parse. (Github issue #5403)

• __qualname__ and __module__ were not available inside of class bodies. (Github issue #4447)

• noexcept was not automatically applied to function pointer attributes in extern structs. Patch by Matúš Valo. (Github issue #5359)

• Function signatures containing a type like tuple[()] could not be printed. Patch by Lisandro Dalcin. (Github issue #5355)

• Extension type hierarchies were generated in the wrong order, thus leading to compile issues. Patch by Lisandro Dalcin. (Github issue #5395)

• Using the --working option could lead to sources not being found. Patch by Lisandro Dalcin. (Github issue #5365)

• Some C compiler warnings were resolved. Patches by Matt Tyson, Lisandro Dalcin, Philipp Wagner, Matti Picus et al. (Github issues #5417, #5418, #5421, #5437, #5438, #5443)

• Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.35 (2023-05-24) release.

Other changes

• For-loops now release the internal reference to their list/tuple iterable before instead of after the else: clause. This probably has no practical impact. (Github issue #5347)

• Simple tuple types like (int, int) are no longer accepted in Python annotations and require the Python notation instead (e.g. tuple[cython.int, cython.int]). (Github issue #5397)

• The code except +nogil (declaring a C++ exception handler function called nogil) is now rejected because it is almost certainly a typo from except + nogil. (Github issue #5430)

3.0.0 beta 2 (2023-03-27)

Features added

• C++ declarations for <cmath>, <numbers> and std::any were added. Patches by Jonathan Helgert and Maximilien Colange. (Github issues #5262, #5309, #5314)

Bugs fixed

• Unintended internal exception handling lead to a visible performance regression for nogil memoryview code in 3.0.0b1. (Github issue #5324)

• None default arguments for arguments with fused memoryview types could select a different implementation in 3.0 than in 0.29.x. The selection behaviour is generally considered suboptimal but was at least reverted to the old behaviour for now. (Github issue #5297)

• The new complex vs. floating point behaviour of the ** power operator accidentally added a dependency on the GIL, which was really only required on failures. (Github issue #5287)

• from cython cimport … as … could lead to imported names not being found in annotations. Patch by Chia-Hsiang Cheng. (Github issue #5235)

• Generated NumPy ufuncs could crash for large arrays due to incorrect GIL handling. (Github issue #5328)

• Very long Python integer constants could exceed the maximum C name length of MSVC. Patch by 0dminnimda. (Github issue #5290)

• cimport_from_pyx could miss some declarations. Patch by Chia-Hsiang Cheng. (Github issue #5318)

• Fully qualified C++ names prefixed by a cimported module name could fail to compile. Patch by Chia-Hsiang Cheng. (Github issue #5229)

• Cython generated C++ code accidentally used C++11 features in some cases. (Github issue #5316)

• Some C++ warnings regarding const usage in internally generated utility code were resolved. Patch by Max Bachmann. (Github issue #5301)

• With language_level=2, imports of modules in packages could return the wrong module in Python 3. (Github issue #5308)

• typing.Optional could fail on tuple types. (Github issue #5263)

• Auto-generated utility code didn’t always have all required user defined types available. (Github issue #5269)

• Type checks for Python’s memoryview type generated incorrect C code. (Github issues #5268, #5270)

• Some issues with depfile generation were resolved. Patches by Eli Schwartz. (Github issues #5279, #5291)

• Some C code issue were resolved for the Limited API target. (Github issues #5264, #5265, #5266)

• The C code shown in the annotated HTML output could lack the last C code line(s).

3.0.0 beta 1 (2023-02-25)

Features added

• Cython implemented C functions now propagate exceptions by default, rather than swallowing them in non-object returning function if the user forgot to add an except declaration to the signature. This was a long-standing source of bugs, but can require adding the noexcept declaration to existing functions if exception propagation is really undesired. (Github issue #4280)

• To opt out of the new, safer exception handling behaviour, legacy code can set the new directive legacy_implicit_noexcept=True for a transition period to keep the previous, unsafe behaviour. This directive will eventually be removed in a later release. Patch by Matúš Valo. (Github issue #5094)

• A new function decorator @cython.ufunc automatically generates a (NumPy) ufunc that applies the calculation function to an entire memoryview. (Github issue #4758)

• The ** power operator now behaves more like in Python by returning the correct complex result if required by math. A new cpow directive was added to turn on the previous C-like behaviour. (Github issue #4936)

• The special __*pow__ methods now support the 2- and 3-argument variants. (Github issue #5160)

• Unknown type annotations (e.g. because of typos) now emit a warning at compile time. Patch by Matúš Valo. (Github issue #5070)

• Subscripted builtin types in type declarations (like list[float]) are now better supported. (Github issue #5058)

• Python’s memoryview is now a known builtin type with optimised properties. (Github issue #3798)

• The call-time dispatch for fused memoryview types is less slow. (Github issue #5073)

• Integer comparisons avoid Python coercions if possible. (Github issue #4821)

• The Python Enum of a cpdef enum now inherits from IntFlag to better match both Python and C semantics of enums. (Github issue #2732)

• PEP-614: decorators can now be arbitrary Python expressions. (Github issue #4570)

• cpdef enums can now be pickled. (Github issue #5120)

• Bound C methods can now coerce to Python objects. (Github issues #4890, #5062)

• C arrays can be initialised inside of nogil functions. Patch by Matúš Valo. (Github issue #1662)

• reversed() can now be used together with C++ iteration. Patch by Chia-Hsiang Cheng. (Github issue #5002)

• Standard C/C++ atomic operations are now used for memory views, if available. (Github issue #4925)

• C11 complex.h is now properly detected. (Github issue #2513)

• Nested cppclass definitions are supported. Patch by samaingw. (Github issue #1218)

• cpp_locals no longer have to be “assignable”. (Github issue #4558)

• cythonize --help now also prints information about the supported environment variables. Patch by Matúš Valo. (Github issue #1711)

• Declarations were added for the C++ bit operations, some other parts of C++20 and CPython APIs. Patches by Jonathan Helgert, Dobatymo, William Ayd and Max Bachmann. (Github issues #4962, #5101, #5157, #5163, #5257)

Bugs fixed

• Generator expressions and comprehensions now look up their outer-most iterable on creation, as Python does, and not later on start, as they did previously. (Github issue #1159)

• Type annotations for Python int rejected long under Py2 in the alpha-11 release. They are now ignored again (as always before) when language_level=2, and accept both int and long in Py2 (and only int in Py3) otherwise. (Github issue #4944)

• Calling bound classmethods of builtin types could fail trying to call the unbound method. (Github issue #5051)

• int(Py_UCS4) returned the code point instead of the parsed digit value. (Github issue #5216)

• Several problems with CPython 3.12 were resolved. (Github issue #5238)

• The C float type was not inferred on assignments. (Github issue #5234)

• Memoryviews with object item type were not supported in Python type declarations. (Github issue #4907)

• Iterating over memoryviews in generator expressions could leak a buffer reference. (Github issue #4968)

• Memory views and the internal Cython array type now identify as collections.abc.Sequence by setting the Py_TPFLAGS_SEQUENCE type flag directly. (Github issue #5187)

• __del__ finaliser methods were not always called if they were only inherited. (Github issue #4995)

• Extension types are now explicitly marked as immutable types to prevent them from being considered mutable. Patch by Max Bachmann. (Github issue #5023)

• const types could not be returned from functions. Patch by Mike Graham. (Github issue #5135)

• cdef public functions declared in .pxd files could use an incorrectly mangled C name. Patch by EpigeneMax. (Github issue #2940)

• cdef public functions used an incorrect linkage declaration in C++. Patch by Maximilien Colange. (Github issue #1839)

• C++ post-increment/-decrement operators were not correctly looked up on declared C++ classes, thus allowing Cython declarations to be missing for them and incorrect C++ code to be generated. Patch by Max Bachmann. (Github issue #4536)

• C++ iteration more safely stores the iterable in temporary variables. Patch by Xavier. (Github issue #3828)

• C++ references did not work on fused types. (Github issue #4717)

• The module state struct was not initialised in correct C (before C23), leading to compile errors on Windows. Patch by yudonglin. (Github issue #5169)

• Structs that contained an array field resulted in incorrect C code. Their initialisation now uses memcpy(). Patch by Chia-Hsiang Cheng. (Github issue #5178)

• Nesting fused types in other fused types could fail to specialise the inner type. (Github issue #4725)

• The special methods __matmul__, __truediv__, __floordiv__ failed to type their self argument. (Github issue #5067)

• Coverage analysis failed in projects with a separate source subdirectory. Patch by Sviatoslav Sydorenko and Ruben Vorderman. (Github issue #3636)

• The annotation_typing directive was missing in pure Python mode. Patch by 0dminnimda. (Github issue #5194)

• The @dataclass directive was accidentally inherited by methods and subclasses. (Github issue #4953)

• Some issues with Cython @dataclass arguments, hashing, inheritance and repr() were resolved. (Github issues #4956, #5046)

• cpdef enums no longer use OrderedDict but dict in Python 3.6 and later. Patch by GalaxySnail. (Github issue #5180)

• Larger numbers of extension types with multiple subclasses could take very long to compile. Patch by Scott Wolchok. (Github issue #5139)

• Relative imports failed in compiled __init__.py package modules. Patch by Matúš Valo. (Github issue #3442)

• Some old usages of the deprecated Python imp module were replaced with importlib. Patch by Matúš Valo. (Github issue #4640)

• The cython and cythonize commands ignored non-existing input files without error. Patch by Matúš Valo. (Github issue #4629)

• Invalid and misspelled cython.* module names were not reported as errors. (Github issue #4947)

• Unused **kwargs arguments did not show up in locals(). (Github issue #4899)

• Extended glob paths with /**/ and \**\ for finding source files failed on Windows.

• Annotated HTML generation was missing newlines in 3.0.0a11. (Github issue #4945)

• Some parser issues were resolved. (Github issue #4992)

• setup.cfg was missing from the source distribution. (Github issue #5199)

• Some C/C++ warnings were resolved. Patches by Max Bachmann, Alexander Shadchin, at al. (Github issues #5004, #5005, #5019, #5029, #5096)

• The embedding code no longer calls deprecated C-API functions but uses the new PyConfig API instead on CPython versions that support it (3.8+). Patch by Alexander Shadchin. (Github issue #4895)

• Intel C compilers could complain about unsupported gcc pragmas. Patch by Ralf Gommers. (Github issue #5052)

• Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.33 (2023-01-06) release.

Other changes

• The undocumented, untested and apparently useless syntax from somemodule cimport class/struct/union somename was removed. The type modifier is not needed here and a plain cimport of the name will do. (Github issue #4904)

• C-style array declarations (cdef int a[4]) are now (silently) deprecated in favour of the Java-style cdef int[4] a form. The latter was always available and the Python type declaration syntax already used it exclusively (a: int[4]). Patch by Matúš Valo. (Github issue #5248)

• The wheel building process was migrated to use the cibuildwheel tool. Patch by Thomas Li. (Github issue #4736)

• Wheels now include a compiled parser again, which increases their size a little but gives about a 10% speed-up when running Cython.

• The Tempita module no longer contains HTML processing capabilities, which were found to be broken in Python 3.8 and later. Patch by Marcel Stimberg. (Github issue #3309)

• The Emacs Cython mode file cython-mode.el is now maintained in a separate repo: https://github.com/cython/emacs-cython-mode

• Cython now uses a .dev0 version suffix for unreleased source installations.

3.0.0 alpha 11 (2022-07-31)

Features added

• A new decorator @cython.dataclasses.dataclass was implemented that provides compile time dataclass generation capabilities to cdef classes (extension types). Patch by David Woods. (Github issue #2903). kw_only dataclasses added by Yury Sokov. (Github issue #4794)

• Named expressions (PEP 572) aka. assignment expressions (aka. the walrus operator :=) were implemented. Patch by David Woods. (Github issue #2636)

• Context managers can be written in parentheses. Patch by David Woods. (Github issue #4814)

• Cython avoids raising StopIteration in __next__ methods when possible. Patch by David Woods. (Github issue #3447)

• Some C++ and CPython library declarations were extended and fixed. Patches by Max Bachmann, Till Hoffmann, Julien Jerphanion, Wenjun Si. (Github issues #4530, #4528, #4710, #4746, #4751, #4818, #4762, #4910)

• The cythonize and cython commands have a new option -M / --depfile to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. The cythonize option was already available in Cython 0.29.27 (2022-01-28). Patches by Evgeni Burovski and Eli Schwartz. (Github issue #1214)

• cythonize() and the corresponding CLI command now regenerate the output files also when they already exist but were generated by a different Cython version.

• Memory views and the internal Cython array type now identify as collections.abc.Sequence. Patch by David Woods. (Github issue #4817)

• Cython generators and coroutines now identify as CO_ASYNC_GENERATOR, CO_COROUTINE and CO_GENERATOR accordingly. (Github issue #4902)

• Memory views can use atomic CPU instructions instead of locks in more cases. Patch by Sam Gross. (Github issue #4912)

• The environment variable CYTHON_FORCE_REGEN=1 can be used to force cythonize to regenerate the output files regardless of modification times and changes.

• A new Cython build option --cython-compile-minimal was added to compile only a smaller set of Cython’s own modules, which can be used to reduce the package and install size.

• Improvements to PyTypeObject definitions in pxd wrapping of libpython. Patch by John Kirkham. (Github issue #4699)

Bugs fixed

• Decorators like @cfunc and @ccall could leak into nested functions and classes. Patch by David Woods. (Github issue #4092)

• Exceptions within for-loops that run over memoryviews could lead to a ref-counting error. Patch by David Woods. (Github issue #4662)

• Using memoryview arguments in closures of inner functions could lead to ref-counting errors. Patch by David Woods. (Github issue #4798)

• Several optimised string methods failed to accept None as arguments to their options. Test patch by Kirill Smelkov. (Github issue #4737)

• A regression in 3.0.0a10 was resolved that prevented property setter methods from having the same name as their value argument. Patch by David Woods. (Github issue #4836)

• Typedefs for the bint type did not always behave like bint. Patch by Nathan Manville and 0dminnimda. (Github issue #4660)

• The return type of a fused function is no longer ignored for function pointers, since it is relevant when passing them e.g. as argument into other fused functions. Patch by David Woods. (Github issue #4644)

• The __self__ attribute of fused functions reports its availability correctly with hasattr(). Patch by David Woods. (Github issue #4808)

• pyximport no longer uses the deprecated imp module. Patch by Matúš Valo. (Github issue #4560)

• pyximport failed for long filenames on Windows. Patch by Matti Picus. (Github issue #4630)

• The generated C code failed to compile in CPython 3.11a4 and later. (Github issue #4500)

• A case of undefined C behaviour was resolved in the list slicing code. Patch by Richard Barnes. (Github issue #4734)

• Using the Limited API could report incorrect line numbers in tracebacks.

• A work-around for StacklessPython < 3.8 was disabled in Py3.8 and later. (Github issue #4329)

• Improve conversion between function pointers with non-identical but compatible exception specifications. Patches by David Woods. (Github issues #4770, #4689)

• The runtime size check for imported PyVarObject types was improved to reduce false positives and adapt to Python 3.11. Patch by David Woods. (Github issues #4827, #4894)

• The generated modules no longer import NumPy internally when using fused types but no memoryviews. Patch by David Woods. (Github issue #4935)

• Improve compatibility with forthcoming CPython 3.12 release.

• Limited API C preprocessor warning is compatible with MSVC. Patch by Victor Molina Garcia. (Github issue #4826)

• Some C compiler warnings were fixed. Patch by mwtian. (Github issue #4831)

• The parser allowed some invalid spellings of .... Patch by 0dminnimda. (Github issue #4868)

• Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.32 (2022-07-29) release.

Other changes

• When using type annotations, func(x: list) or func(x: ExtType) (and other Python builtin or extension types) no longer allow None as input argument to x. This is consistent with the normal typing semantics in Python, and was a common gotcha for users who did not expect None to be allowed as input. To allow None, use typing.Optional as in func(x: Optional[list]). None is also automatically allowed when it is used as default argument, i.e. func(x: list = None). int and float are now also recognised in type annotations and restrict the value type at runtime. They were previously ignored. Note that, for backwards compatibility reasons, the new behaviour does not apply when using Cython’s C notation, as in func(list x). Here, None is still allowed, as always. Also, the annotation_typing directive can now be enabled and disabled more finely within the module. (Github issues #3883, #2696, #4669, #4606, #4886)

• The compile-time DEF and IF statements are deprecated and generate a warning. They should be replaced with normal constants, code generation or C macros. (Github issue #4310)

• Reusing an extension type attribute name as a method name is now an error. Patch by 0dminnimda. (Github issue #4661)

• Improve compatibility between classes pickled in Cython 3.0 and 0.29.x by accepting MD5, SHA-1 and SHA-256 checksums. (Github issue #4680)

3.0.0 alpha 10 (2022-01-06)

Features added

• Cython.Distutils.build_ext now uses cythonize() internally (previously known as new_build_ext), while still supporting the options that were available in the old implementation (old_build_ext). Patch by Matúš Valo. (Github issue #3541)

• pyximport now uses cythonize() internally. Patch by Matúš Valo. (Github issue #2304)

• __del__(self) on extension types now maps to tp_finalize in Python 3. Original patch by ax487. (Github issue #3612)

• Conversion from Python dict to C++ map now supports arbitrary Python mappings, not just dicts.

• Direct assignments to C++ references are now allowed. Patch by David Woods. (Github issue #1863)

• An initial set of adaptations for GraalVM Python was implemented. Note that this does not imply any general support for this target or that your code will work at all in this environment. But testing should be possible now. Patch by David Woods. (Github issue #4328)

• PyMem_[Raw]Calloc() was added to the cpython.mem declarations. Note that the Raw versions are no longer #defined by Cython. The previous macros were not considered safe. Patch by William Schwartz and David Woods. (Github issue #3047)

Bugs fixed

• Circular imports of compiled modules could fail needlessly even when the import could already be resolved from sys.modules. Patch by Syam Gadde. (Github issue #4390)

• The GIL can now safely be released inside of nogil functions (which may actually be called with the GIL held at runtime). Patch by David Woods. (Github issue #4137)

• Type errors when passing memory view arguments could leak buffer references. Patch by David Woods. (Github issue #4296)

• Cython did not type the self argument in special binary methods. Patch by David Woods. (Github issue #4434)

• An incompatibility with recent coverage.py versions was resolved. Patch by David Woods. (Github issue #4440)

• Fused typed default arguments generated incorrect code. Patch by David Woods. (Github issue #4413)

• prange loops generated incorrect code when cpp_locals is enabled. Patch by David Woods. (Github issue #4354)

• A C-level compatibility issue with recent NumPy versions was resolved. Patch by David Woods. (Github issue #4396)

• Decorators on inner functions were not evaluated in the right scope. Patch by David Woods. (Github issue #4367)

• Very early errors during module initialisation could lead to crashes. Patch by David Woods. (Github issue #4377)

• Fused functions were binding unnecessarily, which prevented them from being pickled. Patch by David Woods. (Github issue #4370)

• Some constant tuples containing strings were not deduplicated. Patch by David Woods. (Github issue #4353)

• Unsupported decorators on cdef functions were not rejected in recent releases. Patch by David Woods. (Github issue #4322)

• The excess arguments in a for-in-range loop with more than 3 arguments to range() were silently ignored. Original patch by Max Bachmann. (Github issue #4550)

• Python object types were not allowed as -> return type annotations. Patch by Matúš Valo. (Github issue #4433)

• Default values for memory views arguments were not properly supported. Patch by Corentin Cadiou. (Github issue #4313)

• Templating C++ classes with memory view types lead to buggy code and is now rejected. Patch by David Woods. (Github issue #3085)

• Several C++ library declarations were added and fixed. Patches by Dobatymo, account-login, Jonathan Helgert, Evgeny Yakimov, GalaxySnail, Max Bachmann. (Github issues #4408, #4419, #4410, #4395, #4423, #4448, #4462, #3293, #4522, #2171, #4531)

• Some compiler problems and warnings were resolved. Patches by David Woods, 0dminnimda, Nicolas Pauss and others. (Github issues #4317, #4324, #4361, #4357)

• The self argument of static methods in .pxd files was incorrectly typed. Patch by David Woods. (Github issue #3174)

• A name collision when including multiple generated API header files was resolved. Patch by David Woods. (Github issue #4308)

• An endless loop in cython-mode.el was resolved. Patch by Johannes Mueller. (Github issue #3218)

• _Py_TPFLAGS_HAVE_VECTORCALL was always set on extension types when using the limited API. Patch by David Woods. (Github issue #4453)

• Some compatibility issues with PyPy were resolved. Patches by Max Bachmann, Matti Picus. (Github issues #4454, #4477, #4478, #4509, #4517)

• A compiler crash when running Cython thread-parallel from distutils was resolved. (Github issue #4503)

• Includes all bug-fixes from the 0.29.26 (2021-12-16) release.

Other changes

• A warning was added when __defaults__ or __kwdefaults__ of Cython compiled functions were re-assigned, since this does not current have an effect. Patch by David Woods. (Github issue #2650)

3.0.0 alpha 9 (2021-07-21)

Features added

• Declarations for libcpp.algorithms, libcpp.set and libcpp.unordered_set were extended. Patch by David Woods. (Github issues #4271, #4273)

• cygdb has a new option --skip-interpreter that allows using a different Python runtime than the one used to generate the debugging information. Patch by Alessandro Molina. (Github issue #4186)

Bugs fixed

• Several issues with the new cpp_locals directive were resolved and its test coverage improved. Patch by David Woods. (Github issues #4266, #4265)

• Generated utility code for C++ conversions no longer depends on several user definable directives that may make it behave incorrectly. Patch by David Woods. (Github issue #4206)

• A reference counting bug in the new @cython.total_ordering decorator was fixed.

• Includes all bug-fixes from the 0.29.24 (2021-07-14) release.

Other changes

• Parts of the documentation were (and are being) rewritten to show the Cython language syntax next to the equivalent Python syntax. Patches by 0dminnimda and Matúš Valo. (Github issue #4187)

3.0.0 alpha 8 (2021-07-02)

Features added

• A @cython.total_ordering decorator has been added to automatically implement all comparison operators, similar to functools.total_ordering. Patch by Spencer Brown. (Github issue #2090)

• A new directive cpp_locals was added that allows local C++ variables to be lazily initialised (without default constructor), thus making them behave more like Python variables. Patch by David Woods. (Github issue #4160)

• C++17 execution policies are supported in libcpp.algorithm. Patch by Ashwin Srinath. (Github issue #3790)

• New C feature flags: CYTHON_USE_MODULE_STATE, CYTHON_USE_TYPE_SPECS Both are currently considered experimental. (Github issue #3611)

• [...] * N is optimised for C integer multipliers N. (Github issue #3922)

Bugs fixed

• The dispatch code for binary operators to special methods could run into infinite recursion. Patch by David Woods. (Github issue #4172)

• Code optimisations were not applied to methods of Cython implemented C++ classes. Patch by David Woods. (Github issue #4212)

• The special cython module was not always detected in PEP-484 type annotations. Patch by David Woods. (Github issue #4243)

• Conversion from Python dicts to std::map was broken. Patch by David Woods and Mikkel Skofelt. (Github issues #4231, #4228)

• The exception handling annotation except +* was broken. Patch by David Woods. (Github issues #3065, #3066)

• Attribute annotations in Python classes are now ignored, because they are just Python objects in a dict (as opposed to the fields of extension types). Patch by David Woods. (Github issues #4196, #4198)

• An unnecessary slow-down at import time was removed from Cython.Distutils. Original patch by Anthony Sottile. (Github issue #4224)

• Python modules were not automatically recompiled when only their .pxd file changed. Patch by Golden Rockefeller. (Github issue #1428)

• The signature of PyFloat_FromString() in cpython.float was changed to match the signature in Py3. It still has an automatic fallback for Py2. (Github issue #3909)

• A compile error on MSVC was resolved. Patch by David Woods. (Github issue #4202)

• A C compiler warning in PyPy3 regarding PyEval_EvalCode() was resolved.

• Directives starting with optimization.* in pure Python mode were incorrectly named. It should have been optimize.*. Patch by David Woods. (Github issue #4258)

Other changes

• Variables can no longer be declared with cpdef. Patch by David Woods. (Github issue #887)

• Support for the now unsupported Pyston V1 was removed in favour of Pyston V2. Patch by Marius Wachtler. (Github issue #4211)

• The Cython.Build.BuildExecutable tool no longer executes the program automatically. Use cythonrun for that.

3.0.0 alpha 7 (2021-05-24)

Features added

• A cimport is now supported in pure Python code by prefixing the imported module name with cython.cimports., e.g. from cython.cimports.libc.math import sin. (GIthub issue #4190)

• __class_getitem__ (PEP-560) is supported for cdef classes. Patch by Kmol Yuan. (Github issue #3764)

• __mro_entries__ (PEP-560) is supported for Python classes. Patch by David Woods. (Github issue #3537)

• cython.array supports simple, non-strided views. (Github issue #3775)

• Self-documenting f-strings (=) were implemented. Patch by davfsa. (Github issue #3796)

• The destructor is now called for fields in C++ structs. Patch by David Woods. (Github issue #3226)

• std::move() is now also called for temps during yield. Patch by Yu Feng. (Github issue #4154)

• asyncio.iscoroutinefunction() now recognises coroutine functions also when compiled by Cython. Patch by Pedro Marques da Luz. (Github issue #2273)

• C compiler warnings and errors are now shown in Jupyter notebooks. Patch by Egor Dranischnikow. (Github issue #3751)

• float(…) is optimised for string arguments (str/bytes/bytearray).

• Converting C++ containers to Python lists uses less memory allocations. Patch by Max Bachmann. (Github issue #4081)

• Docstrings of cpdef enums are now copied to the enum class. Patch by matham. (Github issue #3805)

• The type cython.Py_hash_t is available in Python mode.

• C-API declarations for cpython.fileobject were added. Patch by Zackery Spytz. (Github issue #3906)

• C-API declarations for context variables in Python 3.7 were added. Original patch by Zolisa Bleki. (Github issue #2281)

• More C-API declarations for cpython.datetime were added. Patch by Bluenix2. (Github issue #4128)

• A new module cpython.time was added with some low-level alternatives to Python’s time module. Patch by Brock Mendel. (Github issue #3767)

• The value PyBUF_MAX_NDIM was added to the cpython.buffer module. Patch by John Kirkham. (Github issue #3811)

• “Declaration after use” is now an error for variables. Patch by David Woods. (Github issue #3976)

• More declarations for C++ string methods were added.

• Cython now detects when existing output files were not previously generated by itself and refuses to overwrite them. It is a common mistake to name the module file of a wrapper after the library (source file) that it wraps, which can lead to surprising errors when the file gets overwritten.

Bugs fixed

• Annotations were not exposed on annotated (data-)classes. Patch by matsjoyce. (Github issue #4151)

• Inline functions and other code in .pxd files could accidentally inherit the compiler directives of the .pyx file that imported them. Patch by David Woods. (Github issue #1071)

• Some issues were resolved that could lead to duplicated C names. Patch by David Woods. (Github issue #3716, #3741, #3734)

• Modules with unicode names failed to build on Windows. Patch by David Woods. (Github issue #4125)

• ndarray.shape failed to compile with Pythran and recent NumPy. Patch by Serge Guelton. (Github issue #3762)

• Casting to ctuples is now allowed. Patch by David Woods. (Github issue #3808)

• Structs could not be instantiated with positional arguments in pure Python mode.

• Literal list assignments to pointer variables declared in PEP-526 notation failed to compile.

• Nested C++ types were not usable through ctypedefs. Patch by Vadim Pushtaev. (Github issue #4039)

• Overloaded C++ static methods were lost. Patch by Ashwin Srinath. (Github #1851)

• Cython compiled functions always provided a __self__ attribute, regardless of being used as a method or not. Patch by David Woods. (Github issue #4036)

• Calls to .__class__() of a known extension type failed. Patch by David Woods. (Github issue #3954)

• Generator expressions in pxd-overridden cdef functions could fail to compile. Patch by Matúš Valo. (Github issue #3477)

• A reference leak on import failures was resolved. Patch by Max Bachmann. (Github issue #4056)

• A C compiler warning about unused code was resolved. (Github issue #3763)

• A C compiler warning about enum value casting was resolved in GCC. (Github issue #2749)

• Some C compiler warninge were resolved. Patches by Max Bachmann. (Github issue #4053, #4059, #4054, #4148, #4162)

• A compile failure for C++ enums in Py3.4 / MSVC was resolved. Patch by Ashwin Srinath. (Github issue #3782)

• Some C++ STL methods did not propagate exceptions. Patch by Max Bachmann. (Github issue #4079)

• An unsupported C-API call in PyPy was fixed. Patch by Max Bachmann. (Github issue #4055)

• The Cython CodeWriter mishandled no-argument return statements. Patch by Tao He. (Github issue #3795)

• complex wasn’t supported in PEP-484 type annotations. Patch by David Woods. (Github issue #3949)

• Default arguments of methods were not exposed for introspection. Patch by Vladimir Matveev. (Github issue #4061)

• Extension types inheriting from Python classes could not safely be exposed in .pxd files. (Github issue #4106)

• The profiling/tracing code was adapted to work with Python 3.10b1.

• The internal CPython macro Py_ISSPACE() is no longer used. Original patch by Andrew Jones. (Github issue #4111)

• Includes all bug-fixes from the 0.29.23 (2021-04-14) release.

3.0.0 alpha 6 (2020-07-31)

Features added

• Special methods for binary operators now follow Python semantics. Rather than e.g. a single __add__ method for cdef classes, where “self” can be either the first or second argument, one can now define both __add__ and __radd__ as for standard Python classes. This behavior can be disabled with the c_api_binop_methods directive to return to the previous semantics in Cython code (available from Cython 0.29.20), or the reversed method (__radd__) can be implemented in addition to an existing two-sided operator method (__add__) to get a backwards compatible implementation. (Github issue #2056)

• No/single argument functions now accept keyword arguments by default in order to comply with Python semantics. The marginally faster calling conventions METH_NOARGS and METH_O that reject keyword arguments are still available with the directive @cython.always_allow_keywords(False). (Github issue #3090)

• For-in-loop iteration over bytearray and memory views is optimised. Patch by David Woods. (Github issue #2227)

• Type inference now works for memory views and slices. Patch by David Woods. (Github issue #2227)

• The @returns() decorator propagates exceptions by default for suitable C return types when no @exceptval() is defined. (Github issues #3625, #3664)

• A low-level inline function total_seconds(timedelta) was added to cpython.datetime to bypass the Python method call. Note that this function is not guaranteed to give exactly the same results for very large time intervals. Patch by Brock Mendel. (Github issue #3616)

• Type inference now understands that a, *b = x assigns a list to b.

• Limited API support was improved. Patches by Matthias Braun. (Github issues #3693, #3707)

• The Cython CodeWriter can now handle more syntax constructs. Patch by Tao He. (Github issue #3514)

Bugs fixed

• The construct for x in cpp_function_call() failed to compile. Patch by David Woods. (Github issue #3663)

• C++ references failed to compile when used as Python object indexes. Patch by David Woods. (Github issue #3754)

• The C++ typeid() function was allowed in C mode. Patch by Celelibi. (Github issue #3637)

• repr() was assumed to return str instead of unicode with language_level=3. (Github issue #3736)

• Includes all bug-fixes from the 0.29.21 (2020-07-09) release.

Other changes

• The numpy declarations were updated. Patch by Brock Mendel. (Github issue #3630)

• The names of Cython’s internal types (functions, generator, coroutine, etc.) are now qualified with the module name of the internal Cython module that is used for sharing them across Cython implemented modules, for example _cython_3_0a5.coroutine. This was done to avoid making them look like homeless builtins, to help with debugging, and in order to avoid a CPython warning according to https://bugs.python.org/issue20204

3.0.0 alpha 5 (2020-05-19)

Features added

• .pxd files can now be versioned by adding an extension like “.cython-30.pxd” to prevent older Cython versions (than 3.0 in this case) from picking them up. (Github issue #3577)

• Several macros/functions declared in the NumPy API are now usable without holding the GIL.

• libc.math was extended to include all C99 function declarations. Patch by Dean Scarff. (Github issue #3570)

Bugs fixed

• Several issues with arithmetic overflow handling were resolved, including undefined behaviour in C. Patch by Sam Sneddon. (Github issue #3588)

• The improved GIL handling in nogil functions introduced in 3.0a3 could fail to acquire the GIL in some cases on function exit. (Github issue #3590 etc.)

• A reference leak when processing keyword arguments in Py2 was resolved, that appeared in 3.0a1. (Github issue #3578)

• The outdated getbuffer/releasebuffer implementations in the NumPy declarations were removed so that buffers declared as ndarray now use the normal implementation in NumPy.

• Includes all bug-fixes from the 0.29.18 (2020-05-18) release.

3.0.0 alpha 4 (2020-05-05)

Features added

• The print statement (not the print() function) is allowed in nogil code without an explicit with gil section.

• The assert statement is allowed in nogil sections. Here, the GIL is only acquired if the AssertionError is really raised, which means that the evaluation of the asserted condition only allows C expressions.

• Cython generates C compiler branch hints for unlikely user defined if-clauses in more cases, when they end up raising exceptions unconditionally. This now includes exceptions being raised in nogil/with gil sections.

• Some internal memoryview functions were tuned to reduce object overhead.

Bugs fixed

• Exception position reporting could run into race conditions on threaded code. It now uses function-local variables again.

• Error handling early in the module init code could lead to a crash.

• Error handling in cython.array creation was improved to avoid calling C-API functions with an error held.

• Complex buffer item types of structs of arrays could fail to validate. Patch by Leo and smutch. (Github issue #1407)

• When importing the old Cython build_ext integration with distutils, the additional command line arguments leaked into the regular command. Patch by Kamekameha. (Github issue #2209)

• The improved GIL handling in nogil functions introduced in 3.0a3 could generate invalid C code. (Github issue #3558)

• PyEval_InitThreads() is no longer used in Py3.7+ where it is a no-op.

• Parallel builds of Cython itself (setup.py build_ext -j N) failed on Windows.

Other changes

• The C property feature has been rewritten and now requires C property methods to be declared inline (#3571).

3.0.0 alpha 3 (2020-04-27)

Features added

• nogil functions now avoid acquiring the GIL on function exit if possible even if they contain with gil blocks. (Github issue #3554)

• Python private name mangling now falls back to unmangled names for non-Python globals, since double-underscore names are not uncommon in C. Unmangled Python names are also still found as a legacy fallback but produce a warning. Patch by David Woods. (Github issue #3548)

Bugs fixed

• Includes all bug-fixes from the 0.29.17 (2020-04-26) release.

3.0.0 alpha 2 (2020-04-23)

Features added

• std::move() is now used in C++ mode for internal temp variables to make them work without copying values. Patch by David Woods. (Github issues #3253, #1612)

• __class_getitem__ is supported for types on item access (PEP-560). Patch by msg555. (Github issue #2753)

• The simplified Py3.6 customisation of class creation is implemented (PEP-487). (Github issue #2781)

• Conditional blocks in Python code that depend on cython.compiled are eliminated at an earlier stage, which gives more freedom in writing replacement Python code. Patch by David Woods. (Github issue #3507)

• numpy.import_array() is automatically called if numpy has been cimported and it has not been called in the module code. This is intended as a hidden fail-safe so user code should continue to call numpy.import_array. Patch by David Woods. (Github issue #3524)

• The Cython AST code serialiser class CodeWriter in Cython.CodeWriter supports more syntax nodes.

• The fastcall/vectorcall protocols are used for several internal Python calls. (Github issue #3540)

Bugs fixed

• With language_level=3/3str, Python classes without explicit base class are now new-style (type) classes also in Py2. Previously, they were created as old-style (non-type) classes. (Github issue #3530)

• C++ typeid() failed for fused types. Patch by David Woods. (Github issue #3203)

• __arg argument names in methods were not mangled with the class name. Patch by David Woods. (Github issue #1382)

• Creating an empty unicode slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3531)

• Decoding an empty bytes/char* slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3534)

• Temporary buffer indexing variables were not released and could show up in C compiler warnings, e.g. in generators. Patch by David Woods. (Github issues #3430, #3522)

• Several C compiler warnings were fixed.

3.0.0 alpha 1 (2020-04-12)

Features added

• Cython functions now use the PEP-590 vectorcall protocol in Py3.7+. Patch by Jeroen Demeyer. (Github issue #2263)

• Unicode identifiers are supported in Cython code (PEP-3131). Patch by David Woods. (Github issue #2601)

• Unicode module names and imports are supported. Patch by David Woods. (Github issue #3119)

• Annotations are no longer parsed, keeping them as strings following PEP-563. Patch by David Woods. (Github issue #3285)

• Preliminary support for the CPython’s Py_LIMITED_API (stable ABI) is available by setting the CYTHON_LIMITED_API C macro. Note that the support is currently in an early stage and many features do not yet work. You currently still have to define Py_LIMITED_API externally in order to restrict the API usage. This will change when the feature stabilises. Patches by Eddie Elizondo and David Woods. (Github issues #3223, #3311, #3501)

• The dispatch to fused functions is now linear in the number of arguments, which makes it much faster, often 2x or more, and several times faster for larger fused types with many specialisations. Patch by will-ca. (Github issue #1385)

• with gil/nogil statements can be conditional based on compile-time constants, e.g. fused type checks. Patch by Noam Hershtig. (Github issue #2579)

• const can be used together with fused types. Patch by Thomas Vincent. (Github issue #1772)

• Reimports of already imported modules are substantially faster. (Github issue #2854)

• Positional-only arguments are supported in Python functions (PEP-570). Patch by Josh Tobin. (Github issue #2915)

• The volatile C modifier is supported in Cython code. Patch by Jeroen Demeyer. (Github issue #1667)

• @cython.trashcan(True) can be used on an extension type to enable the CPython Enabling the deallocation trashcan. This allows deallocating deeply recursive objects without overflowing the stack. Patch by Jeroen Demeyer. (Github issue #2842)

• Inlined properties can be defined for external extension types. Patch by Matti Picus. (Github issue #2640, redone later in #3571)

• The str() builtin now calls PyObject_Str() instead of going through a Python call. Patch by William Ayd. (Github issue #3279)

• String concatenation can now happen in place if possible, by extending the existing string rather than always creating a new one. Patch by David Woods. (Github issue #3453)

• Multiplication of Python numbers with small constant integers is faster. (Github issue #2808)

• Some list copying is avoided internally when a new list needs to be created but we already have a fresh one. (Github issue #3494)

• Extension types that do not need their own tp_new implementation (because they have no object attributes etc.) directly inherit the implementation of their parent type if possible. (Github issue #1555)

• The attributes gen.gi_frame and coro.cr_frame of Cython compiled generators and coroutines now return an actual frame object for introspection. (Github issue #2306)

• Several declarations in cpython.*, libc.* and libcpp.* were added. Patches by Jeroen Demeyer, Matthew Edwards, Chris Gyurgyik, Jerome Kieffer and Zackery Spytz. (Github issues #3468, #3332, #3202, #3188, #3179, #2891, #2826, #2713)

• Deprecated NumPy API usages were removed from numpy.pxd. Patch by Matti Picus. (Github issue #3365)

• cython.inline() now sets the NPY_NO_DEPRECATED_API=NPY_1_7_API_VERSION C macro automatically when numpy is imported in the code, to avoid C compiler warnings about deprecated NumPy C-API usage.

• The builtin abs() function can now be used on C numbers in nogil code. Patch by Elliott Sales de Andrade. (Github issue #2748)

• PEP-479 (generator_stop) is now enabled by default with language level 3. (Github issue #2580)

• The cython.view.array type supports inheritance. Patch by David Woods. (Github issue #3413)

• Code annotation accepts a new debugging argument --annotate-fullc that will include the complete syntax highlighted C file in the HTML output. (Github issue #2855)

• --no-capture added to runtests.py to prevent stdout/stderr capturing during srctree tests. Patch by Matti Picus. (Github issue #2701)

• --no-docstrings option added to cythonize script. Original patch by mo-han. (Github issue #2889)

• cygdb gives better error messages when it fails to initialise the Python runtime support in gdb. Patch by Volker Weissmann. (Github issue #3489)

• The Pythran shape attribute is supported. Patch by Serge Guelton. (Github issue #3307)

Bugs fixed

• The unicode methods .upper(), .lower() and .title() were incorrectly optimised for single character input values and only returned the first character if multiple characters should have been returned. They now use the original Python methods again.

• Fused argument types were not correctly handled in type annotations and cython.locals(). Patch by David Woods. (Github issues #3391, #3142)

• Diverging from the usual behaviour, len(memoryview), len(char*) and len(Py_UNICODE*) returned an unsigned size_t value. They now return a signed Py_ssize_t, like other usages of len().

• Nested dict literals in function call kwargs could incorrectly raise an error about duplicate keyword arguments, which are allowed when passing them from dict literals. (Github issue #2963)

• Item access (subscripting) with integer indices/keys always tried the Sequence protocol before the Mapping protocol, which diverged from Python semantics. It now passes through the Mapping protocol first when supported. (Github issue #1807)

• Name lookups in class bodies no longer go through an attribute lookup. Patch by Jeroen Demeyer. (Github issue #3100)

• Broadcast assignments to a multi-dimensional memory view slice could end up in the wrong places when the underlying memory view is known to be contiguous but the slice is not. (Github issue #2941)

• Pickling unbound methods of Python classes failed. Patch by Pierre Glaser. (Github issue #2972)

• The Py_hash_t type failed to accept arbitrary “index” values. (Github issue #2752)

• The first function line number of functions with decorators pointed to the signature line and not the first decorator line, as in Python. Patch by Felix Kohlgrüber. (Github issue #2536)

• Constant integer expressions that used a negative exponent were evaluated as integer 0 instead of the expected float value. Patch by Kryštof Pilnáček. (Github issue #2133)

• The cython.declare() and cython.cast() functions could fail in pure mode. Patch by Dmitry Shesterkin. (Github issue #3244)

• __doc__ was not available inside of the class body during class creation. (Github issue #1635)

• Setting language_level=2 in a file did not work if language_level=3 was enabled globally before. Patch by Jeroen Demeyer. (Github issue #2791)

• __init__.pyx files were not always considered as package indicators. (Github issue #2665)

• Compiling package __init__ files could fail under Windows due to an undefined export symbol. (Github issue #2968)

• A C compiler cast warning was resolved. Patch by Michael Buesch. (Github issue #2775)

• Binding staticmethods of Cython functions were not behaving like Python methods. Patch by Jeroen Demeyer. (Github issue #3106, #3102)

• Memoryviews failed to compile when the cache_builtins feature was disabled. Patch by David Woods. (Github issue #3406)

Other changes

• The default language level was changed to 3str, i.e. Python 3 semantics, but with str literals (also in Python 2.7). This is a backwards incompatible change from the previous default of Python 2 semantics. The previous behaviour is available through the directive language_level=2. (Github issue #2565)

• Cython no longer generates __qualname__ attributes for classes in Python 2.x since they are problematic there and not correctly maintained for subclasses. Patch by Jeroen Demeyer. (Github issue #2772)

• Source file fingerprinting now uses SHA-1 instead of MD5 since the latter tends to be slower and less widely supported these days. (Github issue #2790)

• The long deprecated include files python_*, stdio, stdlib and stl in Cython/Includes/Deprecated/ were removed. Use the libc.* and cpython.* pxd modules instead. Patch by Jeroen Demeyer. (Github issue #2904)

• The search order for include files was changed. Previously it was include_directories, Cython/Includes, sys.path. Now it is include_directories, sys.path, Cython/Includes. This was done to allow third-party *.pxd files to override the ones in Cython. Patch by Matti Picus. (Github issue #2905)

• The command line parser was rewritten and modernised using argparse. Patch by Egor Dranischnikow. (Github issue #2952, #3001)

• Dotted filenames for qualified module names (pkg.mod.pyx) are deprecated. Use the normal Python package directory layout instead. (Github issue #2686)

• Binary Linux wheels now follow the manylinux2010 standard. Patch by Alexey Stepanov. (Github issue #3355)

• Support for Python 2.6 was removed.

0.29.37 (2023-12-18)

Bugs fixed

• Fix a potential crash while cleaning up subtypes of externally imported extension types when terminating Python. This was introduced in Cython 0.29.35.

• Fix a complex related compile error on Windows. (Github issue #5512)

• Compiling fused types used in pxd files could crash Cython in Python 3.11+. (Github issues #5894, #5588)

• cythonize failed to consider the CYTHON_FORCE_REGEN env variable. Patch by Harmen Stoppels. (Github issue #5712)

0.29.36 (2023-07-04)

Bugs fixed

• Async generators lost their return value in PyPy. (Github issue #5465)

• The outdated C macro _PyGC_FINALIZED() is no longer used in Py3.9+.

• The deprecated Py_OptimizeFlag is no longer used in Python 3.9+. (Github issue #5343)

• Using the global __debug__ variable but not assertions could lead to compile errors.

• The broken HTML template support was removed from Tempita. (Github issue #3309)

0.29.35 (2023-05-24)

Bugs fixed

• A garbage collection enabled subtype of a non-GC extension type could call into the deallocation function of the super type with GC tracking enabled. This could lead to crashes during deallocation if GC was triggered on the type at the same time. (Github issue #5432)

• Some C compile failures and crashes in CPython 3.12 were resolved.

• except + nogil was syntactically not allowed. except +nogil (i.e. defining a C++ exception handling function called nogil) is now disallowed to prevent typos. (Github issue #5430)

• A C compile failure in PyPy 3.10 was resolved. Patch by Matti Picus. (Github issue #5408)

• Cython modules now use PEP-489 multi-phase init by default in PyPy 3.9 and later. Original patch by Matti Picus. (Github issue #5413)

• API header files generated by different Cython versions can now be included in the same C file. (Github issue #5383)

• Function signatures containing a type like tuple[()] could not be printed. Patch by Lisandro Dalcin. (Github issue #5355)

0.29.34 (2023-04-02)

Bugs fixed

• A reference leak of the for-loop list/tuple iterable was resolved if the for-loop’s else: branch executes a break for an outer loop. (Github issue #5347)

• Some C compile failures in CPython 3.12 were resolved.

• Some old usages of the deprecated Python imp module were replaced with importlib. Patch by Matúš Valo. (Github issue #5300)

• Some issues with depfile generation were resolved. Patches by Eli Schwartz. (Github issues #5279, #5291)

0.29.33 (2023-01-06)

Features added

• The cythonize and cython commands have a new option -M / --depfile to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. The cythonize option was already available in Cython 0.29.27 (2022-01-28). Patches by Evgeni Burovski and Eli Schwartz. (Github issue #1214)

Bugs fixed

• const fused types could not be used with memory views. Patch by Thomas Vincent. (Github issue #1772)

• wstr usage was removed in Python 3.12 and later (PEP-623). (Github issue #5145)

• A type check assertion for Cython functions failed in debug Python builds. (Github issue #5031)

• Fixed various compiler warnings. Patches by Lisandro Dalcin et al. (Github issues #4948, #5086)

• Fixed error when calculating complex powers of negative numbers. (Github issue #5014)

• Corrected a small mis-formatting of exception messages on Python 2. (Github issue #5018)

• The PyUnicode_AsUTF8AndSize() C-API function was missing from the CPython declarations. (Github issue #5163)

• A performance problem in the compiler was resolved when nesting conditional expressions. (Github issue #5197)

• Test suite problems with recent NumPy and CPython versions were resolved. (Github issues #5183, #5190)

Other changes

• The undocumented, untested and apparently useless syntax from somemodule cimport class/struct/union somename was deprecated in anticipation of its removal in Cython 3. The type modifier is not needed here and a plain cimport of the name will do. (Github issue #4905)

• Properly disable generation of descriptor docstrings on PyPy since they cause crashes. It was previously disabled, but only accidentally via a typo. Patch by Matti Picus. (Github issue #5083)

• The cpow directive of Cython 3.0 is available as a no-op. (Github issue #5016)

0.29.32 (2022-07-29)

Bugs fixed

• Revert “Using memoryview typed arguments in inner functions is now rejected as unsupported.” Patch by David Woods. (Github issue #4798)

• from module import * failed in 0.29.31 when using memoryviews. Patch by David Woods. (Github issue #4927)

0.29.31 (2022-07-27)

Features added

• A new argument --module-name was added to the cython command to provide the (one) exact target module name from the command line. Patch by Matthew Brett and h-vetinari. (Github issue #4906)

• A new keyword noexcept was added for forward compatibility with Cython 3. Patch by David Woods. (Github issue #4903)

Bugs fixed

• Use importlib.util.find_spec() instead of the deprecated importlib.find_loader() function when setting up the package path at import-time. Patch by Matti Picus. (Github issue #4764)

• Require the C compiler to support the two-arg form of va_start on Python 3.10 and higher. Patch by Thomas Caswell. (Github issue #4820)

• Make fused_type subscriptable in Shadow.py. Patch by Pfebrer. (Github issue #4842)

• Fix the incorrect code generation of the target type in bytearray loops. Patch by Kenrick Everett. (Github issue #4108)

• Atomic refcounts for memoryviews were not used on some GCC versions by accident. Patch by Sam Gross. (Github issue #4915)

• Silence some GCC -Wconversion warnings in C utility code. Patch by Lisandro Dalcin. (Github issue #4854)

• Tuple multiplication was ignored in expressions such as [*(1,) * 2]. Patch by David Woods. (Github issue #4864)

• Calling append methods on extension types could fail to find the method in some cases. Patch by David Woods. (Github issue #4828)

• Ensure that object buffers (e.g. ndarray[object, ndim=1]) containing NULL pointers are safe to use, returning None instead of the NULL pointer. Patch by Sebastian Berg. (Github issue #4859)

• Using memoryview typed arguments in inner functions is now rejected as unsupported. Patch by David Woods. (Github issue #4798)

• Compilation could fail on systems (e.g. FIPS) that block MD5 checksums at runtime. (Github issue #4909)

• Experimental adaptations for the CPython “nogil” fork was added. Note that there is no official support for this in Cython 0.x. Patch by Sam Gross. (Github issue #4912)

0.29.30 (2022-05-16)

Bugs fixed

• The GIL handling changes in 0.29.29 introduced a regression where objects could be deallocated without holding the GIL. (Github issue #4796)

0.29.29 (2022-05-16)

Features added

• Avoid acquiring the GIL at the end of nogil functions. This change was backported in order to avoid generating wrong C code that would trigger C compiler warnings with tracing support enabled. Backport by Oleksandr Pavlyk. (Github issue #4637)

Bugs fixed

• Function definitions in finally: clauses were not correctly generated. Patch by David Woods. (Github issue #4651)

• A case where C-API functions could be called with a live exception set was fixed. Patch by Jakub Kulík. (Github issue #4722)

• Pickles can now be exchanged again with those generated from Cython 3.0 modules. (Github issue #4680)

• Cython now correctly generates Python methods for both the provided regular and reversed special numeric methods of extension types. Patch by David Woods. (Github issue #4750)

• Calling unbound extension type methods without arguments could raise an IndexError instead of a TypeError. Patch by David Woods. (Github issue #4779)

• Calling unbound .__contains__() super class methods on some builtin base types could trigger an infinite recursion. Patch by David Woods. (Github issue #4785)

• The C union type in pure Python mode mishandled some field names. Patch by Jordan Brière. (Github issue #4727)

• Allow users to overwrite the C macro _USE_MATH_DEFINES. Patch by Yuriy Chernyshov. (Github issue #4690)

• Improved compatibility with CPython 3.10/11. Patches by Thomas Caswell, David Woods. (Github issues #4609, #4667, #4721, #4730, #4777)

• Docstrings of descriptors are now provided in PyPy 7.3.9. Patch by Matti Picus. (Github issue #4701)

0.29.28 (2022-02-17)

Bugs fixed

• Due to backwards incompatible changes in CPython 3.11a4, the feature flags CYTHON_FAST_THREAD_STATE and CYTHON_USE_EXC_INFO_STACK are now disabled in Python 3.11 and later. They are enabled again in Cython 3.0. Patch by David Woods. (Github issue #4610)

• A C compiler warning in older PyPy versions was resolved. Patch by Matti Picus. (Github issue #4236)

0.29.27 (2022-01-28)

Features added

• The cythonize command has a new option -M to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. Patch by Evgeni Burovski. (Github issue #1214)

Bugs fixed

• Compilation failures on PyPy were resolved. Patches by Matti Picus. (Github issues #4509, #4517)

• Calls to range() with more than three arguments did not fail. Original patch by Max Bachmann. (Github issue #4550)

• Some C compiler warnings about missing type struct initialisers in Py3.10 were resolved.

• Cython no longer warns about using OpenMP 3.0 features since they are now considered generally available.

0.29.26 (2021-12-16)

Bugs fixed

• An incompatibility with CPython 3.11.0a3 was resolved. (Github issue #4499)

• The in operator failed on literal lists with starred expressions. Patch by Arvind Natarajan. (Github issue #3938)

• A C compiler warning in PyPy about a missing struct field initialisation was resolved.

0.29.25 (2021-12-06)

Bugs fixed

• Several incompatibilities with CPython 3.11 were resolved. Patches by David Woods, Victor Stinner, Thomas Caswell. (Github issues #4411, #4414, #4415, #4416, #4420, #4428, #4473, #4479, #4480)

• Some C compiler warnings were resolved. Patches by Lisandro Dalcin and others. (Github issue #4439)

• C++ std::move() should only be used automatically in MSVC versions that support it. Patch by Max Bachmann. (Github issue #4191)

• The Py_hash_t type failed to accept arbitrary “index” values. (Github issue #2752)

• Avoid copying unaligned 16-bit values since some platforms require them to be aligned. Use memcpy() instead to let the C compiler decide how to do it. (Github issue #4343)

• Cython crashed on invalid truthiness tests on C++ types without operator bool. Patch by David Woods. (Github issue #4348)

• The declaration of PyUnicode_CompareWithASCIIString() in cpython.unicode was incorrect. Patch by Max Bachmann. (Github issue #4344)

0.29.24 (2021-07-14)

Bugs fixed

• Inline functions in pxd files that used memory views could lead to invalid C code if the module that imported from them does not use memory views. Patch by David Woods. (Github issue #1415)

• Several declarations in libcpp.string were added and corrected. Patch by Janek Bevendorff. (Github issue #4268)

• Pickling unbound Cython compiled methods failed. Patch by Pierre Glaser. (Github issue #2972)

• The tracing code was adapted to work with CPython 3.10.

• The optimised in operator failed on unicode strings in Py3.9 and later that were constructed from an external wchar_t source. Also, related C compiler warnings about deprecated C-API usage were resolved. (Github issue #3925)

• Some compiler crashes were resolved. Patch by David Woods. (Github issues #4214, #2811)

• An incorrect warning about ‘unused’ generator expressions was removed. (GIthub issue #1699)

• The attributes gen.gi_frame and coro.cr_frame of Cython compiled generators and coroutines now return an actual frame object for introspection, instead of None. (Github issue #2306)

0.29.23 (2021-04-14)

Bugs fixed

• Some problems with Python 3.10 were resolved. Patches by Victor Stinner and David Woods. (Github issues #4046, #4100)

• An incorrect “optimisation” was removed that allowed changes to a keyword dict to leak into keyword arguments passed into a function. Patch by Peng Weikang. (Github issue #3227)

• Multiplied str constants could end up as bytes constants with language_level=2. Patch by Alphadelta14 and David Woods. (Github issue #3951)

• PY_SSIZE_T_CLEAN does not get defined any more if it is already defined. Patch by Andrew Jones. (Github issue #4104)

0.29.22 (2021-02-20)

Features added

• Some declarations were added to the provided pxd includes. Patches by Zackery Spytz and John Kirkham. (Github issues #3811, #3882, #3899, #3901)

Bugs fixed

• A crash when calling certain functions in Py3.9 and later was resolved. (Github issue #3917)

• const memory views of structs failed to compile. (Github issue #2251)

• const template declarations could not be nested. Patch by Ashwin Srinath. (Github issue #1355)

• The declarations in the cpython.pycapsule module were missing their const modifiers and generated incorrect C code. Patch by Warren Weckesser. (Github issue #3964)

• Casts to memory views failed for fused dtypes. Patch by David Woods. (Github issue #3881)

• repr() was assumed to return str instead of unicode with language_level=3. (Github issue #3736)

• Calling cpdef functions from cimported modules crashed the compiler. Patch by David Woods. (Github issue #4000)

• Cython no longer validates the ABI size of the NumPy classes it compiled against. See the discussion in https://github.com/numpy/numpy/pull/432

• A C compiler warning about enum value casting was resolved in GCC. (Github issue #2749)

• Coverage reporting in the annotated HTML file failed in Py3.9. Patch by Nick Pope. (Github issue #3865)

• The embedding code now reports Python errors as exit status.

• Long type declarations could lead to (harmless) random changes in the C file when used in auto-generated Python wrappers or pickled classes.

Other changes

• Variables defined as cpdef now generate a warning since this is currently useless and thus does not do what users would expect. Patch by David Woods. (Github issue #3959)

0.29.21 (2020-07-09)

Bugs fixed

• Fix a regression in 0.29.20 where __div__ failed to be found in extension types. (Github issue #3688)

• Fix a regression in 0.29.20 where a call inside of a finally clause could fail to compile. Patch by David Woods. (Github issue #3712)

• Zero-sized buffers could fail to validate as C/Fortran-contiguous. Patch by Clemens Hofreither. (Github issue #2093)

• exec() did not allow recent Python syntax features in Py3.8+ due to https://bugs.python.org/issue35975. (Github issue #3695)

• Binding staticmethods of Cython functions were not behaving like Python methods in Py3. Patch by Jeroen Demeyer and Michał Górny. (Github issue #3106)

• Pythran calls to NumPy methods no longer generate useless method lookup code.

• The PyUnicode_GET_LENGTH() macro was missing from the cpython.* declarations. Patch by Thomas Caswell. (Github issue #3692)

• The deprecated PyUnicode_*() C-API functions are no longer used, except for Unicode strings that contain lone surrogates. Unicode strings that contain non-BMP characters or surrogate pairs now generate different C code on 16-bit Python 2.x Unicode deployments (such as MS-Windows). Generating the C code on Python 3.x is recommended in this case. Original patches by Inada Naoki and Victor Stinner. (Github issues #3677, #3721, #3697)

• Some template parameters were missing from the C++ std::unordered_map declaration. Patch by will. (Github issue #3685)

• Several internal code generation issues regarding temporary variables were resolved. (Github issue #3708)

0.29.20 (2020-06-10)

Bugs fixed

• Nested try-except statements with multiple return statements could crash due to incorrect deletion of the except as target variable. (Github issue #3666)

• The @classmethod decorator no longer rejects unknown input from other decorators. Patch by David Woods. (Github issue #3660)

• Fused types could leak into unrelated usages. Patch by David Woods. (Github issue #3642)

• Now uses Py_SET_SIZE() and Py_SET_REFCNT() in Py3.9+ to avoid low-level write access to these object fields. Patch by Victor Stinner. (Github issue #3639)

• The built-in abs() function could lead to undefined behaviour when used on the negative-most value of a signed C integer type. Patch by Serge Guelton. (Github issue #1911)

• Usages of sizeof() and typeid() on uninitialised variables no longer produce a warning. Patch by Celelibi. (Github issue #3575)

• The C++ typeid() function was allowed in C mode. Patch by Celelibi. (Github issue #3637)

• The error position reported for errors found in f-strings was misleading. (Github issue #3674)

• The new c_api_binop_methods directive was added for forward compatibility, but can only be set to True (the current default value). It can be disabled in Cython 3.0.

0.29.19 (2020-05-20)

Bugs fixed

• A typo in Windows specific code in 0.29.18 was fixed that broke “libc.math”. (Github issue #3622)

• A platform specific test failure in 0.29.18 was fixed. Patch by smutch. (Github issue #3620)

0.29.18 (2020-05-18)

Bugs fixed

• Exception position reporting could run into race conditions on threaded code. It now uses function-local variables again.

• Error handling early in the module init code could lead to a crash.

• Error handling in cython.array creation was improved to avoid calling C-API functions with an error held.

• A memory corruption was fixed when garbage collection was triggered during calls to PyType_Ready() of extension type subclasses. (Github issue #3603)

• Memory view slicing generated unused error handling code which could negatively impact the C compiler optimisations for parallel OpenMP code etc. Also, it is now helped by static branch hints. (Github issue #2987)

• Cython’s built-in OpenMP functions were not translated inside of call arguments. Original patch by Celelibi and David Woods. (Github issue #3594)

• Complex buffer item types of structs of arrays could fail to validate. Patch by Leo and smutch. (Github issue #1407)

• Decorators were not allowed on nested async def functions. (Github issue #1462)

• C-tuples could use invalid C struct casting. Patch by MegaIng. (Github issue #3038)

• Optimised %d string formatting into f-strings failed on float values. (Github issue #3092)

• Optimised aligned string formatting (%05s, %-5s) failed. (Github issue #3476)

• When importing the old Cython build_ext integration with distutils, the additional command line arguments leaked into the regular command. Patch by Kamekameha. (Github issue #2209)

• When using the CYTHON_NO_PYINIT_EXPORT option in C++, the module init function was not declared as extern "C". (Github issue #3414)

• Three missing timedelta access macros were added in cpython.datetime.

• The signature of the NumPy C-API function PyArray_SearchSorted() was fixed. Patch by Brock Mendel. (Github issue #3606)

0.29.17 (2020-04-26)

Features added

• std::move() is now available from libcpp.utility. Patch by Omer Ozarslan. (Github issue #2169)

• The @cython.binding decorator is available in Python code. (Github issue #3505)

Bugs fixed

• Creating an empty unicode slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3531)

• Decoding an empty bytes/char* slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3534)

• Re-importing a Cython extension no longer raises the error “__reduce_cython__ not found”. (Github issue #3545)

• Unused C-tuples could generate incorrect code in 0.29.16. Patch by Kirk Meyer. (Github issue #3543)

• Creating a fused function attached it to the garbage collector before it was fully initialised, thus risking crashes in rare failure cases. Original patch by achernomorov. (Github issue #3215)

• Temporary buffer indexing variables were not released and could show up in C compiler warnings, e.g. in generators. Patch by David Woods. (Github issues #3430, #3522)

• The compilation cache in cython.inline("…") failed to take the language level into account. Patch by will-ca. (Github issue #3419)

• The deprecated PyUnicode_GET_SIZE() function is no longer used in Py3.

0.29.16 (2020-03-24)

Bugs fixed

• Temporary internal variables in nested prange loops could leak into other threads. Patch by Frank Schlimbach. (Github issue #3348)

• Default arguments on fused functions could crash. Patch by David Woods. (Github issue #3370)

• C-tuples declared in .pxd files could generate incomplete C code. Patch by Kirk Meyer. (Github issue #1427)

• Fused functions were not always detected and optimised as Cython implemented functions. Patch by David Woods. (Github issue #3384)

• Valid Python object concatenation of (iterable) strings to non-strings could fail with an exception. Patch by David Woods. (Github issue #3433)

• Using C functions as temporary values lead to invalid C code. Original patch by David Woods. (Github issue #3418)

• Fix an unhandled C++ exception in comparisons. Patch by David Woods. (Github issue #3361)

• Fix deprecated import of “imp” module. Patch by Matti Picus. (Github issue #3350)

• Fix compatibility with Pythran 0.9.6 and later. Patch by Serge Guelton. (Github issue #3308)

• The _Py_PyAtExit() function in cpython.pylifecycle was misdeclared. Patch by Zackery Spytz. (Github issue #3382)

• Several missing declarations in cpython.* were added. Patches by Zackery Spytz. (Github issue #3452, #3421, #3411, #3402)

• A declaration for libc.math.fpclassify() was added. Patch by Zackery Spytz. (Github issue #2514)

• Avoid “undeclared” warning about automatically generated pickle methods. Patch by David Woods. (Github issue #3353)

• Avoid C compiler warning about unreachable code in prange().

• Some C compiler warnings in PyPy were resolved. Patch by Matti Picus. (Github issue #3437)

0.29.15 (2020-02-06)

Bugs fixed

• Crash when returning a temporary Python object from an async-def function. (Github issue #3337)

• Crash when using **kwargs in generators. Patch by David Woods. (Github issue #3265)

• Double reference free in __class__ cell handling for super() calls. (Github issue #3246)

• Compile error when using *args as Python class bases. (Github issue #3338)

• Import failure in IPython 7.11. (Github issue #3297)

• Fixed C name collision in the auto-pickle code. Patch by ThePrez. (Github issue #3238)

• Deprecated import failed in Python 3.9. (Github issue #3266)

0.29.14 (2019-11-01)

Bugs fixed

• The generated code failed to initialise the tp_print slot in CPython 3.8. Patches by Pablo Galindo and Orivej Desh. (Github issues #3171, #3201)

• ? for bool was missing from the supported NumPy dtypes. Patch by Max Klein. (Github issue #2675)

• await was not allowed inside of f-strings. Patch by Dmitro Getz. (Github issue #2877)

• Coverage analysis failed for projects where the code resides in separate source sub-directories. Patch by Antonio Valentino. (Github issue #1985)

• An incorrect compiler warning was fixed in automatic C++ string conversions. Patch by Gerion Entrup. (Github issue #3108)

• Error reports in the Jupyter notebook showed unhelpful stack traces. Patch by Matthew Edwards (Github issue #3196).

• Python.h is now also included explicitly from public header files. (Github issue #3133).

• Distutils builds with --parallel did not work when using Cython’s deprecated build_ext command. Patch by Alphadelta14 (Github issue #3187).

Other changes

• The PyMemoryView_*() C-API is available in cpython.memoryview. Patch by Nathan Manville. (Github issue #2541)

0.29.13 (2019-07-26)

Bugs fixed

• A reference leak for None was fixed when converting a memoryview to a Python object. (Github issue #3023)

• The declaration of PyGILState_STATE in cpython.pystate was unusable. Patch by Kirill Smelkov. (Github issue #2997)

Other changes

• The declarations in posix.mman were extended. Patches by Kirill Smelkov. (Github issues #2893, #2894, #3012)

0.29.12 (2019-07-07)

Bugs fixed

• Fix compile error in CPython 3.8b2 regarding the PyCode_New() signature. (Github issue #3031)

• Fix a C compiler warning about a missing int downcast. (Github issue #3028)

• Fix reported error positions of undefined builtins and constants. Patch by Orivej Desh. (Github issue #3030)

• A 32 bit issue in the Pythran support was resolved. Patch by Serge Guelton. (Github issue #3032)

0.29.11 (2019-06-30)

Bugs fixed

• Fix compile error in CPython 3.8b2 regarding the PyCode_New() signature. Patch by Nick Coghlan. (Github issue #3009)

• Invalid C code generated for lambda functions in cdef methods. Patch by Josh Tobin. (Github issue #2967)

• Support slice handling in newer Pythran versions. Patch by Serge Guelton. (Github issue #2989)

• A reference leak in power-of-2 calculation was fixed. Patch by Sebastian Berg. (Github issue #3022)

• The search order for include files was changed. Previously it was include_directories, Cython/Includes, sys.path. Now it is include_directories, sys.path, Cython/Includes. This was done to allow third-party *.pxd files to override the ones in Cython. Original patch by Matti Picus. (Github issue #2905)

• Setting language_level=2 in a file did not work if language_level=3 was enabled globally before. Patch by Jeroen Demeyer. (Github issue #2791)

0.29.10 (2019-06-02)

Bugs fixed

• Fix compile errors in CPython 3.8b1 due to the new “tp_vectorcall” slots. (Github issue #2976)

0.29.9 (2019-05-29)

Bugs fixed

• Fix a crash regression in 0.29.8 when creating code objects fails.

• Remove an incorrect cast when using true-division in C++ operations. (Github issue #1950)

0.29.8 (2019-05-28)

Bugs fixed

• C compile errors with CPython 3.8 were resolved. Patch by Marcel Plch. (Github issue #2938)

• Python tuple constants that compare equal but have different item types could incorrectly be merged into a single constant. (Github issue #2919)

• Non-ASCII characters in unprefixed strings could crash the compiler when used with language level 3str.

• Starred expressions in %-formatting tuples could fail to compile for unicode strings. (Github issue #2939)

• Passing Python class references through cython.inline() was broken. (Github issue #2936)

0.29.7 (2019-04-14)

Bugs fixed

• Crash when the shared Cython config module gets unloaded and another Cython module reports an exceptions. Cython now makes sure it keeps an owned reference to the module. (Github issue #2885)

• Resolved a C89 compilation problem when enabling the fast-gil sharing feature.

• Coverage reporting did not include the signature line of cdef functions. (Github issue #1461)

• Casting a GIL-requiring function into a nogil function now issues a warning. (Github issue #2879)

• Generators and coroutines were missing their return type annotation. (Github issue #2884)

0.29.6 (2019-02-27)

Bugs fixed

• Fix a crash when accessing the __kwdefaults__ special attribute of fused functions. (Github issue #1470)

• Fix the parsing of buffer format strings that contain numeric sizes, which could lead to incorrect input rejections. (Github issue #2845)

• Avoid a C #pragma in old gcc versions that was only added in GCC 4.6. Patch by Michael Anselmi. (Github issue #2838)

• Auto-encoding of Unicode strings to UTF-8 C/C++ strings failed in Python 3, even though the default encoding there is UTF-8. (Github issue #2819)

0.29.5 (2019-02-09)

Bugs fixed

• Crash when defining a Python subclass of an extension type and repeatedly calling a cpdef method on it. (Github issue #2823)

• Compiler crash when prange() loops appear inside of with-statements. (Github issue #2780)

• Some C compiler warnings were resolved. Patches by Christoph Gohlke. (Github issues #2815, #2816, #2817, #2822)

• Python conversion of C++ enums failed in 0.29. Patch by Orivej Desh. (Github issue #2767)

0.29.4 (2019-02-01)

Bugs fixed

• Division of numeric constants by a runtime value of 0 could fail to raise a ZeroDivisionError. (Github issue #2820)

0.29.3 (2019-01-19)

Bugs fixed

• Some C code for memoryviews was generated in a non-deterministic order. Patch by Martijn van Steenbergen. (Github issue #2779)

• C89 compatibility was accidentally lost since 0.28. Patches by gastineau and true-pasky. (Github issues #2778, #2801)

• A C compiler cast warning was resolved. Patch by Michael Buesch. (Github issue #2774)

• An compilation failure with complex numbers under MSVC++ was resolved. (Github issue #2797)

• Coverage reporting could fail when modules were moved around after the build. Patch by Wenjun Si. (Github issue #2776)

0.29.2 (2018-12-14)

Bugs fixed

• The code generated for deduplicated constants leaked some references. (Github issue #2750)

• The declaration of sigismember() in libc.signal was corrected. (Github issue #2756)

• Crashes in compiler and test runner were fixed. (Github issue #2736, #2755)

• A C compiler warning about an invalid safety check was resolved. (Github issue #2731)

0.29.1 (2018-11-24)

Bugs fixed

• Extensions compiled with MinGW-64 under Windows could misinterpret integer objects larger than 15 bit and return incorrect results. (Github issue #2670)

• Cython no longer requires the source to be writable when copying its data into a memory view slice. Patch by Andrey Paramonov. (Github issue #2644)

• Line tracing of try-statements generated invalid C code. (Github issue #2274)

• When using the warn.undeclared directive, Cython’s own code generated warnings that are now fixed. Patch by Nicolas Pauss. (Github issue #2685)

• Cython’s memoryviews no longer require strides for setting the shape field but only the PyBUF_ND flag to be set. Patch by John Kirkham. (Github issue #2716)

• Some C compiler warnings about unused memoryview code were fixed. Patch by Ho Cheuk Ting. (Github issue #2588)

• A C compiler warning about implicit signed/unsigned conversion was fixed. (Github issue #2729)

• Assignments to C++ references returned by operator[] could fail to compile. (Github issue #2671)

• The power operator and the support for NumPy math functions were fixed in Pythran expressions. Patch by Serge Guelton. (Github issues #2702, #2709)

• Signatures with memory view arguments now show the expected type when embedded in docstrings. Patch by Matthew Chan and Benjamin Weigel. (Github issue #2634)

• Some from ... cimport ... constructs were not correctly considered when searching modified dependencies in cythonize() to decide whether to recompile a module. Patch by Kryštof Pilnáček. (Github issue #2638)

• A struct field type in the cpython.array declarations was corrected. Patch by John Kirkham. (Github issue #2712)

0.29 (2018-10-14)

Features added

• PEP-489 multi-phase module initialisation has been enabled again. Module reloads in other subinterpreters raise an exception to prevent corruption of the static module state.

• A set of mypy compatible PEP-484 declarations were added for Cython’s C data types to integrate with static analysers in typed Python code. They are available in the Cython/Shadow.pyi module and describe the types in the special cython module that can be used for typing in Python code. Original patch by Julian Gethmann. (Github issue #1965)

• Memoryviews are supported in PEP-484/526 style type declarations. (Github issue #2529)

• @cython.nogil is supported as a C-function decorator in Python code. (Github issue #2557)

• Raising exceptions from nogil code will automatically acquire the GIL, instead of requiring an explicit with gil block.

• C++ functions can now be declared as potentially raising both C++ and Python exceptions, so that Cython can handle both correctly. (Github issue #2615)

• cython.inline() supports a direct language_level keyword argument that was previously only available via a directive.

• A new language level name 3str was added that mostly corresponds to language level 3, but keeps unprefixed string literals as type ‘str’ in both Py2 and Py3, and the builtin ‘str’ type unchanged. This will become the default in the next Cython release and is meant to help user code a) transition more easily to this new default and b) migrate to Python 3 source code semantics without making support for Python 2.x difficult.

• In CPython 3.6 and later, looking up globals in the module dict is almost as fast as looking up C globals. (Github issue #2313)

• For a Python subclass of an extension type, repeated method calls to non-overridden cpdef methods can avoid the attribute lookup in Py3.6+, which makes them 4x faster. (Github issue #2313)

• (In-)equality comparisons of objects to integer literals are faster. (Github issue #2188)

• Some internal and 1-argument method calls are faster.

• Modules that cimport many external extension types from other Cython modules execute less import requests during module initialisation.

• Constant tuples and slices are deduplicated and only created once per module. (Github issue #2292)

• The coverage plugin considers more C file extensions such as .cc and .cxx. (Github issue #2266)

• The cythonize command accepts compile time variable values (as set by DEF) through the new -E option. Patch by Jerome Kieffer. (Github issue #2315)

• pyximport can import from namespace packages. Patch by Prakhar Goel. (Github issue #2294)

• Some missing numpy and CPython C-API declarations were added. Patch by John Kirkham. (Github issues #2523, #2520, #2537)

• Declarations for the pylifecycle C-API functions were added in a new .pxd file cpython.pylifecycle.

• The Pythran support was updated to work with the latest Pythran 0.8.7. Original patch by Adrien Guinet. (Github issue #2600)

• %a is included in the string formatting types that are optimised into f-strings. In this case, it is also automatically mapped to %r in Python 2.x.

• New C macro CYTHON_HEX_VERSION to access Cython’s version in the same style as PY_VERSION_HEX.

• Constants in libc.math are now declared as const to simplify their handling.

• An additional check_size clause was added to the ctypedef class name specification to allow suppressing warnings when importing modules with backwards-compatible PyTypeObject size changes. Patch by Matti Picus. (Github issue #2627)

Bugs fixed

• The exception handling in generators and coroutines under CPython 3.7 was adapted to the newly introduced exception stack. Users of Cython 0.28 who want to support Python 3.7 are encouraged to upgrade to 0.29 to avoid potentially incorrect error reporting and tracebacks. (Github issue #1958)

• Crash when importing a module under Stackless Python that was built for CPython. Patch by Anselm Kruis. (Github issue #2534)

• 2-value slicing of typed sequences failed if the start or stop index was None. Patch by Christian Gibson. (Github issue #2508)

• Multiplied string literals lost their factor when they are part of another constant expression (e.g. ‘x’ * 10 + ‘y’ => ‘xy’).

• String formatting with the ‘%’ operator didn’t call the special __rmod__() method if the right side is a string subclass that implements it. (Python issue 28598)

• The directive language_level=3 did not apply to the first token in the source file. (Github issue #2230)

• Overriding cpdef methods did not work in Python subclasses with slots. Note that this can have a performance impact on calls from Cython code. (Github issue #1771)

• Fix declarations of builtin or C types using strings in pure python mode. (Github issue #2046)

• Generator expressions and lambdas failed to compile in @cfunc functions. (Github issue #459)

• Global names with const types were not excluded from star-import assignments which could lead to invalid C code. (Github issue #2621)

• Several internal function signatures were fixed that lead to warnings in gcc-8. (Github issue #2363)

• The numpy helper functions set_array_base() and get_array_base() were adapted to the current numpy C-API recommendations. Patch by Matti Picus. (Github issue #2528)

• Some NumPy related code was updated to avoid deprecated API usage. Original patch by jbrockmendel. (Github issue #2559)

• Several C++ STL declarations were extended and corrected. Patch by Valentin Valls. (Github issue #2207)

• C lines of the module init function were unconditionally not reported in exception stack traces. Patch by Jeroen Demeyer. (Github issue #2492)

• When PEP-489 support is enabled, reloading the module overwrote any static module state. It now raises an exception instead, given that reloading is not actually supported.

• Object-returning, C++ exception throwing functions were not checking that the return value was non-null. Original patch by Matt Wozniski (Github issue #2603)

• The source file encoding detection could get confused if the c_string_encoding directive appeared within the first two lines. (Github issue #2632)

• Cython generated modules no longer emit a warning during import when the size of the NumPy array type is larger than what was found at compile time. Instead, this is assumed to be a backwards compatible change on NumPy side.

Other changes

• Cython now emits a warning when no language_level (2, 3 or ‘3str’) is set explicitly, neither as a cythonize() option nor as a compiler directive. This is meant to prepare the transition of the default language level from currently Py2 to Py3, since that is what most new users will expect these days. The future default will, however, not enforce unicode literals, because this has proven a major obstacle in the support for both Python 2.x and 3.x. The next major release is intended to make this change, so that it will parse all code that does not request a specific language level as Python 3 code, but with str literals. The language level 2 will continue to be supported for an indefinite time.

• The documentation was restructured, cleaned up and examples are now tested. The NumPy tutorial was also rewritten to simplify the running example. Contributed by Gabriel de Marmiesse. (Github issue #2245)

• Cython compiles less of its own modules at build time to reduce the installed package size to about half of its previous size. This makes the compiler slightly slower, by about 5-7%.

0.28.6 (2018-11-01)

Bugs fixed

• Extensions compiled with MinGW-64 under Windows could misinterpret integer objects larger than 15 bit and return incorrect results. (Github issue #2670)

• Multiplied string literals lost their factor when they are part of another constant expression (e.g. ‘x’ * 10 + ‘y’ => ‘xy’).

0.28.5 (2018-08-03)

Bugs fixed

• The discouraged usage of GCC’s attribute optimize("Os") was replaced by the similar attribute cold to reduce the code impact of the module init functions. (Github issue #2494)

• A reference leak in Py2.x was fixed when comparing str to unicode for equality.

0.28.4 (2018-07-08)

Bugs fixed

• Reallowing tp_clear() in a subtype of an @no_gc_clear extension type generated an invalid C function call to the (non-existent) base type implementation. (Github issue #2309)

• Exception catching based on a non-literal (runtime) tuple could fail to match the exception. (Github issue #2425)

• Compile fix for CPython 3.7.0a2. (Github issue #2477)

0.28.3 (2018-05-27)

Bugs fixed

• Set iteration was broken in non-CPython since 0.28.

• UnicodeEncodeError in Py2 when %s formatting is optimised for unicode strings. (Github issue #2276)

• Work around a crash bug in g++ 4.4.x by disabling the size reduction setting of the module init function in this version. (Github issue #2235)

• Crash when exceptions occur early during module initialisation. (Github issue #2199)

0.28.2 (2018-04-13)

Features added

• abs() is faster for Python long objects.

• The C++11 methods front() and end() were added to the declaration of libcpp.string. Patch by Alex Huszagh. (Github issue #2123)

• The C++11 methods reserve() and bucket_count() are declared for libcpp.unordered_map. Patch by Valentin Valls. (Github issue #2168)

Bugs fixed

• The copy of a read-only memoryview was considered read-only as well, whereas a common reason to copy a read-only view is to make it writable. The result of the copying is now a writable buffer by default. (Github issue #2134)

• The switch statement generation failed to apply recursively to the body of converted if-statements.

• NULL was sometimes rejected as exception return value when the returned type is a fused pointer type. Patch by Callie LeFave. (Github issue #2177)

• Fixed compatibility with PyPy 5.11. Patch by Matti Picus. (Github issue #2165)

Other changes

• The NumPy tutorial was rewritten to use memoryviews instead of the older buffer declaration syntax. Contributed by Gabriel de Marmiesse. (Github issue #2162)

0.28.1 (2018-03-18)

Bugs fixed

• PyFrozenSet_New() was accidentally used in PyPy where it is missing from the C-API.

• Assignment between some C++ templated types were incorrectly rejected when the templates mix const with ctypedef. (Github issue #2148)

• Undeclared C++ no-args constructors in subclasses could make the compilation fail if the base class constructor was declared without nogil. (Github issue #2157)

• Bytes %-formatting inferred basestring (bytes or unicode) as result type in some cases where bytes would have been safe to infer. (Github issue #2153)

• None was accidentally disallowed as typed return value of dict.pop(). (Github issue #2152)

0.28 (2018-03-13)

Features added

• Cdef classes can now multiply inherit from ordinary Python classes. (The primary base must still be a c class, possibly object, and the other bases must not be cdef classes.)

• Type inference is now supported for Pythran compiled NumPy expressions. Patch by Nils Braun. (Github issue #1954)

• The const modifier can be applied to memoryview declarations to allow read-only buffers as input. (Github issues #1605, #1869)

• C code in the docstring of a cdef extern block is copied verbatimly into the generated file. Patch by Jeroen Demeyer. (Github issue #1915)

• When compiling with gcc, the module init function is now tuned for small code size instead of whatever compile flags were provided externally. Cython now also disables some code intensive optimisations in that function to further reduce the code size. (Github issue #2102)

• Decorating an async coroutine with @cython.iterable_coroutine changes its type at compile time to make it iterable. While this is not strictly in line with PEP-492, it improves the interoperability with old-style coroutines that use yield from instead of await.

• The IPython magic has preliminary support for JupyterLab. (Github issue #1775)

• The new TSS C-API in CPython 3.7 is supported and has been backported. Patch by Naotoshi Seo. (Github issue #1932)

• Cython knows the new Py_tss_t type defined in PEP-539 and automatically initialises variables declared with that type to Py_tss_NEEDS_INIT, a value which cannot be used outside of static assignments.

• The set methods .remove() and .discard() are optimised. Patch by Antoine Pitrou. (Github issue #2042)

• dict.pop() is optimised. Original patch by Antoine Pitrou. (Github issue #2047)

• Iteration over sets and frozensets is optimised. (Github issue #2048)

• Safe integer loops (< range(2^30)) are automatically optimised into C loops.

• alist.extend([a,b,c]) is optimised into sequential list.append() calls for short literal sequences.

• Calls to builtin methods that are not specifically optimised into C-API calls now use a cache that avoids repeated lookups of the underlying C function. (Github issue #2054)

• Single argument function calls can avoid the argument tuple creation in some cases.

• Some redundant extension type checks are avoided.

• Formatting C enum values in f-strings is faster, as well as some other special cases.

• String formatting with the ‘%’ operator is optimised into f-strings in simple cases.

• Subscripting (item access) is faster in some cases.

• Some bytearray operations have been optimised similar to bytes.

• Some PEP-484/526 container type declarations are now considered for loop optimisations.

• Indexing into memoryview slices with view[i][j] is now optimised into view[i, j].

• Python compatible cython.* types can now be mixed with type declarations in Cython syntax.

• Name lookups in the module and in classes are faster.

• Python attribute lookups on extension types without instance dict are faster.

• Some missing signals were added to libc/signal.pxd. Patch by Jeroen Demeyer. (Github issue #1914)

• The warning about repeated extern declarations is now visible by default. (Github issue #1874)

• The exception handling of the function types used by CPython’s type slot functions was corrected to match the de-facto standard behaviour, so that code that uses them directly benefits from automatic and correct exception propagation. Patch by Jeroen Demeyer. (Github issue #1980)

• Defining the macro CYTHON_NO_PYINIT_EXPORT will prevent the module init function from being exported as symbol, e.g. when linking modules statically in an embedding setup. Patch by AraHaan. (Github issue #1944)

Bugs fixed

• If a module name is explicitly provided for an Extension() that is compiled via cythonize(), it was previously ignored and replaced by the source file name. It can now be used to override the target module name, e.g. for compiling prefixed accelerator modules from Python files. (Github issue #2038)

• The arguments of the num_threads parameter of parallel sections were not sufficiently validated and could lead to invalid C code. (Github issue #1957)

• Catching exceptions with a non-trivial exception pattern could call into CPython with a live exception set. This triggered incorrect behaviour and crashes, especially in CPython 3.7.

• The signature of the special __richcmp__() method was corrected to recognise the type of the first argument as self. It was previously treated as plain object, but CPython actually guarantees that it always has the correct type. Note: this can change the semantics of user code that previously relied on self being untyped.

• Some Python 3 exceptions were not recognised as builtins when running Cython under Python 2.

• Some async helper functions were not defined in the generated C code when compiling simple async code. (Github issue #2075)

• Line tracing did not include generators and coroutines. (Github issue #1949)

• C++ declarations for unordered_map were corrected. Patch by Michael Schatzow. (Github issue #1484)

• Iterator declarations in C++ deque and vector were corrected. Patch by Alex Huszagh. (Github issue #1870)

• The const modifiers in the C++ string declarations were corrected, together with the coercion behaviour of string literals into C++ strings. (Github issue #2132)

• Some declaration types in libc.limits were corrected. Patch by Jeroen Demeyer. (Github issue #2016)

• @cython.final was not accepted on Python classes with an @cython.cclass decorator. (Github issue #2040)

• Cython no longer creates useless and incorrect PyInstanceMethod wrappers for methods in Python 3. Patch by Jeroen Demeyer. (Github issue #2105)

• The builtin bytearray type could not be used as base type of cdef classes. (Github issue #2106)

Other changes

0.27.3 (2017-11-03)

Bugs fixed

• String forward references to extension types like @cython.locals(x="ExtType") failed to find the named type. (Github issue #1962)

• NumPy slicing generated incorrect results when compiled with Pythran. Original patch by Serge Guelton (Github issue #1946).

• Fix “undefined reference” linker error for generators on Windows in Py3.3-3.5. (Github issue #1968)

• Adapt to recent C-API change of PyThreadState in CPython 3.7.

• Fix signature of PyWeakref_GetObject() API declaration. Patch by Jeroen Demeyer (Github issue #1975).

0.27.2 (2017-10-22)

Bugs fixed

• Comprehensions could incorrectly be optimised away when they appeared in boolean test contexts. (Github issue #1920)

• The special methods __eq__, __lt__ etc. in extension types did not type their first argument as the type of the class but object. (Github issue #1935)

• Crash on first lookup of “cline_in_traceback” option during exception handling. (Github issue #1907)

• Some nested module level comprehensions failed to compile. (Github issue #1906)

• Compiler crash on some complex type declarations in pure mode. (Github issue #1908)

• std::unordered_map.erase() was declared with an incorrect void return type in libcpp.unordered_map. (Github issue #1484)

• Invalid use of C++ fallthrough attribute before C++11 and similar issue in clang. (Github issue #1930)

• Compiler crash on misnamed properties. (Github issue #1905)

0.27.1 (2017-10-01)

Features added

• The Jupyter magic has a new debug option --verbose that shows details about the distutils invocation. Patch by Boris Filippov (Github issue #1881).

Bugs fixed

• Py3 list comprehensions in class bodies resulted in invalid C code. (Github issue #1889)

• Modules built for later CPython 3.5.x versions failed to import in 3.5.0/3.5.1. (Github issue #1880)

• Deallocating fused types functions and methods kept their GC tracking enabled, which could potentially lead to recursive deallocation attempts.

• Crash when compiling in C++ mode with old setuptools versions. (Github issue #1879)

• C++ object arguments for the constructor of Cython implemented C++ are now passed by reference and not by value to allow for non-copyable arguments, such as unique_ptr.

• API-exported C++ classes with Python object members failed to compile. (Github issue #1866)

• Some issues with the new relaxed exception value handling were resolved.

• Python classes as annotation types could prevent compilation. (Github issue #1887)

• Cython annotation types in Python files could lead to import failures with a “cython undefined” error. Recognised types are now turned into strings.

• Coverage analysis could fail to report on extension modules on some platforms.

• Annotations could be parsed (and rejected) as types even with annotation_typing=False.

Other changes

• PEP 489 support has been disabled by default to counter incompatibilities with import setups that try to reload or reinitialise modules.

0.27 (2017-09-23)

Features added

• Extension module initialisation follows PEP 489 in CPython 3.5+, which resolves several differences with regard to normal Python modules. This makes the global names __file__ and __path__ correctly available to module level code and improves the support for module-level relative imports. (Github issues #1715, #1753, #1035)

• Asynchronous generators (PEP 525) and asynchronous comprehensions (PEP 530) have been implemented. Note that async generators require finalisation support in order to allow for asynchronous operations during cleanup, which is only available in CPython 3.6+. All other functionality has been backported as usual.

• Variable annotations are now parsed according to PEP 526. Cython types (e.g. cython.int) are evaluated as C type declarations and everything else as Python types. This can be disabled with the directive annotation_typing=False. Note that most complex PEP-484 style annotations are currently ignored. This will change in future releases. (Github issue #1850)

• Extension types (also in pure Python mode) can implement the normal special methods __eq__, __lt__ etc. for comparisons instead of the low-level __richcmp__ method. (Github issue #690)

• New decorator @cython.exceptval(x=None, check=False) that makes the signature declarations except x, except? x and except * available to pure Python code. Original patch by Antonio Cuni. (Github issue #1653)

• Signature annotations are now included in the signature docstring generated by the embedsignature directive. Patch by Lisandro Dalcin (Github issue #1781).

• The gdb support for Python code (libpython.py) was updated to the latest version in CPython 3.7 (git rev 5fe59f8).

• The compiler tries to find a usable exception return value for cdef functions with except * if the returned type allows it. Note that this feature is subject to safety limitations, so it is still better to provide an explicit declaration.

• C functions can be assigned to function pointers with a compatible exception declaration, not only with exact matches. A side-effect is that certain compatible signature overrides are now allowed and some more mismatches of exception signatures are now detected and rejected as errors that were not detected before.

• The IPython/Jupyter magic integration has a new option %%cython --pgo for profile guided optimisation. It compiles the cell with PGO settings for the C compiler, executes it to generate a runtime profile, and then compiles it again using that profile for C compiler optimisation. Currently only tested with gcc.

• len(memoryview) can be used in nogil sections to get the size of the first dimension of a memory view (shape[0]). (Github issue #1733)

• C++ classes can now contain (properly refcounted) Python objects.

• NumPy dtype subarrays are now accessible through the C-API. Patch by Gerald Dalley (Github issue #245).

• Resolves several issues with PyPy and uses faster async slots in PyPy3. Patch by Ronan Lamy (Github issues #1871, #1878).

Bugs fixed

• Extension types that were cimported from other Cython modules could disagree about the order of fused cdef methods in their call table. This could lead to wrong methods being called and potentially also crashes. The fix required changes to the ordering of fused methods in the call table, which may break existing compiled modules that call fused cdef methods across module boundaries, if these methods were implemented in a different order than they were declared in the corresponding .pxd file. (Github issue #1873)

• The exception state handling in generators and coroutines could lead to exceptions in the caller being lost if an exception was raised and handled inside of the coroutine when yielding. (Github issue #1731)

• Loops over range(enum) were not converted into C for-loops. Note that it is still recommended to use an explicit cast to a C integer type in this case.

• Error positions of names (e.g. variables) were incorrectly reported after the name and not at the beginning of the name.

• Compile time DEF assignments were evaluated even when they occur inside of falsy IF blocks. (Github issue #1796)

• Disabling the line tracing from a trace function could fail. Original patch by Dmitry Trofimov. (Github issue #1769)

• Several issues with the Pythran integration were resolved.

• abs(signed int) now returns a signed rather than unsigned int. (Github issue #1837)

• Reading frame.f_locals of a Cython function (e.g. from a debugger or profiler could modify the module globals. (Github issue #1836)

• Buffer type mismatches in the NumPy buffer support could leak a reference to the buffer owner.

• Using the “is_f_contig” and “is_c_contig” memoryview methods together could leave one of them undeclared. (Github issue #1872)

• Compilation failed if the for-in-range loop target was not a variable but a more complex expression, e.g. an item assignment. (Github issue #1831)

• Compile time evaluations of (partially) constant f-strings could show incorrect results.

• Escape sequences in raw f-strings (fr'...') were resolved instead of passing them through as expected.

• Some ref-counting issues in buffer error handling have been resolved.

Other changes

• Type declarations in signature annotations are now parsed according to PEP 484 typing. Only Cython types (e.g. cython.int) and Python builtin types are currently considered as type declarations. Everything else is ignored, but this will change in a future Cython release. (Github issue #1672)

• The directive annotation_typing is now True by default, which enables parsing type declarations from annotations.

• This release no longer supports Python 3.2.

0.26.1 (2017-08-29)

Features added

Bugs fixed

• cython.view.array was missing .__len__().

• Extension types with a .pxd override for their __releasebuffer__ slot (e.g. as provided by Cython for the Python array.array type) could leak a reference to the buffer owner on release, thus not freeing the memory. (Github issue #1638)

• Auto-decoding failed in 0.26 for strings inside of C++ containers. (Github issue #1790)

• Compile error when inheriting from C++ container types. (Github issue #1788)

• Invalid C code in generators (declaration after code). (Github issue #1801)

• Arithmetic operations on const integer variables could generate invalid code. (Github issue #1798)

• Local variables with names of special Python methods failed to compile inside of closures. (Github issue #1797)

• Problem with indirect Emacs buffers in cython-mode. Patch by Martin Albrecht (Github issue #1743).

• Extension types named result or PickleError generated invalid unpickling code. Patch by Jason Madden (Github issue #1786).

• Bazel integration failed to compile .py files. Patch by Guro Bokum (Github issue #1784).

• Some include directories and dependencies were referenced with their absolute paths in the generated files despite lying within the project directory.

• Failure to compile in Py3.7 due to a modified signature of _PyCFunctionFast()

0.26 (2017-07-19)

Features added

• Pythran can be used as a backend for evaluating NumPy array expressions. Patch by Adrien Guinet (Github issue #1607).

• cdef classes now support pickling by default when possible. This can be disabled with the auto_pickle directive.

• Speed up comparisons of strings if their hash value is available. Patch by Claudio Freire (Github issue #1571).

• Support pyximport from zip files. Patch by Sergei Lebedev (Github issue #1485).

• IPython magic now respects the __all__ variable and ignores names with leading-underscore (like import * does). Patch by Syrtis Major (Github issue #1625).

• abs() is optimised for C complex numbers. Patch by David Woods (Github issue #1648).

• The display of C lines in Cython tracebacks can now be enabled at runtime via import cython_runtime; cython_runtime.cline_in_traceback=True. The default has been changed to False.

• The overhead of calling fused types generic functions was reduced.

• “cdef extern” include files are now also searched relative to the current file. Patch by Jeroen Demeyer (Github issue #1654).

• Optional optimization for re-acquiring the GIL, controlled by the fast_gil directive.

Bugs fixed

• Item lookup/assignment with a unicode character as index that is typed (explicitly or implicitly) as Py_UCS4 or Py_UNICODE used the integer value instead of the Unicode string value. Code that relied on the previous behaviour now triggers a warning that can be disabled by applying an explicit cast. (Github issue #1602)

• f-string processing was adapted to changes in PEP 498 and CPython 3.6.

• Invalid C code when decoding from UTF-16(LE/BE) byte strings. (Github issue #1696)

• Unicode escapes in ‘ur’ raw-unicode strings were not resolved in Py2 code. Original patch by Aaron Gallagher (Github issue #1594).

• File paths of code objects are now relative. Original patch by Jelmer Vernooij (Github issue #1565).

• Decorators of cdef class methods could be executed twice. Patch by Jeroen Demeyer (Github issue #1724).

• Dict iteration using the Py2 iter* methods failed in PyPy3. Patch by Armin Rigo (Github issue #1631).

• Several warnings in the generated code are now suppressed.

Other changes

• The unraisable_tracebacks option now defaults to True.

• Coercion of C++ containers to Python is no longer automatic on attribute access (Github issue #1521).

• Access to Python attributes of cimported modules without the corresponding import is now a compile-time (rather than runtime) error.

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