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 :issue:`6989`)

* ``cython.pythread_type_lock`` (also used as fallback for ``cython.pymutex``)
  could stall on heavily contended locks.
  (Github issue :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 :issue:`7020`)

* Unterminated ``\N{}`` character escapes in strings could unrail the parser.
  (Github issue :issue:`7056`)

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

* Some Unicode letters were not recognised as lexically valid name parts.
  (Github issue :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 :issue:`7038`)

3.1.2 (2025-06-08)

==================

Bugs fixed
----------

* Attribute lookups failed on the ``bool`` builtin type.
  (Github issue :issue:`6905`)

* Type checks on or-ed union types could incorrectly return false.
  (Github issue :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 :issue:`6924`)

* Calls to C functions taking exception types failed to check for a `None` argument.
  (Github issue :issue:`6420`)

* Fused functions had an incorrect ``__module__`` attribute.
  (Github issue :issue:`6897`)

* The type of Cython implemented functions had an incorrect ``__module__`` attribute.
  (Github issue :issue:`6841`)

* Errors while indexing into ``bytearray`` or ``str`` in ``nogil`` sections could crash.
  (Github issue :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 :issue:`6896`)

* ``PyDict_GetItemStringRef()`` was accidentally used in older Limited API versions.
  (Github issue :issue:`6914`)

* ``abort()`` was used but not always available in the Limited API.
  (Github issue :issue:`6918`)

* Some dependencies were missing from the ``depfile``.
  (Github issue :issue:`6938`)

* Embedded function signatures were not always separated from the existing docstring.
  (Github issue :issue:`6904`)

* ``numpy.math`` was missing from ``Cython/Includes/`` and could not be cimported.
  (Github issue :issue:`6859`)

* Some tests were adapted for NumPy 2.x.
  (Github issue :issue:`6898`)

* Some C compiler warnings were fixed.
  (Github issue :issue:`6870`)

* ``Cython.Build`` was not officially exposing the ``cythonize`` function.
  (Github issue :issue:`6934`)

3.1.1 (2025-05-19)

==================

Bugs fixed
----------

* A reference leak in the async delegation code was fixed.
  (Github issues :issue:`6850`, :issue:`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 :issue:`6854`)

* Some Limited API issues were resolved.
  (Github issue :issue:`6862`)

* Large C ``long long`` values could be truncated when passed into PyPy.
  (Github issue :issue:`6890`)

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

* The signature of fused functions was no longer introspectable in Cython 3.1.0.
  (Github issue :issue:`6855`)

* Coroutines could generate invalid C with line tracing enabled.
  (Github issue :issue:`6865`)

* Code using ``complex()`` could generate invalid C code missing type declarations.
  (Github issue :issue:`6860`)

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

* Code using ctuples in a ``const`` context could generate invalid C.
  (Github issue :issue:`6864`)

* Accessing special methods on cpdef enums failed to compile.

* Some C compiler warnings were resolved.
  Patches by Daniel Larraz.  (Github issues :issue:`6876`, :issue:`3172`, :issue:`6873`, :issue:`6877`)

* Re-establish support for PyPy 3.8.
  (Github issue :issue:`6867`)

3.1.0 (2025-05-08)

==================

Features added
--------------

3.1.0 rc 2 (2025-05-07):

* 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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6842)

3.1.0 rc 1 (2025-05-01):

* ``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 https://github.com/cython/cython/issues/6579)

* A new directive ``subinterpreters_compatible=shared_gil/own_gil`` was added to allow modules
  to declare support for subinterpreters.
  (Github issue https://github.com/cython/cython/issues/6513)

* ``divmod()`` is also optimised for C floating point types and can be called on C number types
  without holding the GIL.
  (Github issue https://github.com/cython/cython/issues/6801)

* New C++ declarations were added.
  (Github issues https://github.com/cython/cython/issues/6625, https://github.com/cython/cython/issues/6731)

* ``embedsignature`` now works for special methods (if they have a docstring).
  (Github issue https://github.com/cython/cython/issues/1577)

3.1.0 beta 1 (2025-04-03):

* Global ``cdef const …`` variables are supported.
  (Github issue https://github.com/cython/cython/issues/6542)

* A new context manager / function decorator ``cython.critical_section`` was added
  wrapping Python's critical section C-API feature.
  (Github issues https://github.com/cython/cython/issues/6516, https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/2356)

* The type of ``prange`` loop targets is now inferred.
  (Github issue https://github.com/cython/cython/issues/6585)

* Extracting keyword arguments is faster in some cases.
  (Github issue https://github.com/cython/cython/issues/6683)

* Calling ``divmod()`` on any C integer types is efficient.
  (Github issue https://github.com/cython/cython/issues/6717)

* Some async/coroutine/vectorcall code has improved fast-paths.
  (Github issues https://github.com/cython/cython/issues/6732, https://github.com/cython/cython/issues/6735, https://github.com/cython/cython/issues/6736, https://github.com/cython/cython/issues/6738, https://github.com/cython/cython/issues/6742, https://github.com/cython/cython/issues/6771)

* Calls to Python builtins and extension types use the vectorcall protocol.
  (Github issue https://github.com/cython/cython/issues/6744)

* Method calls use ``PyObject_VectorcallMethod()`` where possible.
  (Github issue https://github.com/cython/cython/issues/6747)

* Some C-API shortcuts were (re-)added.
  (Github issue https://github.com/cython/cython/issues/6761)

* Cython can avoid normalising exceptions in an `except` clause if it knows that they are unused.
  (Github issue https://github.com/cython/cython/issues/6601)

* The ``cython`` command has a new option ``--cache`` to cache generated files.
  (Github issue https://github.com/cython/cython/issues/6091)

* The ``cythonize`` command has a new option ``--timeit`` to benchmark Cython code snippets.
  (Github issue https://github.com/cython/cython/issues/6697)

* The argument parsing ``cygdb`` command was improved based on ``argparse``.
  Patch by William Ayd.  (Github issue https://github.com/cython/cython/issues/5499)

* The ``PyWeakref_GetRef`` declaration was added to ``cpython.weakref`` and backported.
  Patch by Lysandros Nikolaou.  (Github issue https://github.com/cython/cython/issues/6478)

* ``std::span`` declarations were added to ``libcpp``.
  Patch by Alexander Condello.  (Github issue https://github.com/cython/cython/issues/6539)

* ``std::string_view`` declarations were added to ``libcpp``.
  Patch by Antoine Pitrou.  (Github issue https://github.com/cython/cython/issues/6539)

* Mutex declarations for ``libc`` and  ``libcpp`` were added.
  (Github issue https://github.com/cython/cython/issues/6610)

* Several C++ declarations were improved and extended.
  Patches by Yury V. Zaytsev.  (Github issues https://github.com/cython/cython/issues/488, https://github.com/cython/cython/issues/489)

* Bazel build rules were updated for better interoperability.
  Patch by maleo.  (Github issue https://github.com/cython/cython/issues/6478)

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

3.1.0 alpha 1 (2024-11-08):

* 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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5955, https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6254)

* ``cython.const[]`` and ``cython.volatile[]`` are now available as type modifiers in Python code.
  (Github issue https://github.com/cython/cython/issues/5728)

* ``cython.pointer[SomeCType]`` can now be used to define pointer types in Python type annotations.
  (Github issue https://github.com/cython/cython/issues/5071)

* Several improvements were made to reduce the size of the resulting extension modules.
  (Github issue https://github.com/cython/cython/issues/4425)

* Function calls now use the PEP-590 Vectorcall protocol, even when passing keyword arguments.
  (Github issues https://github.com/cython/cython/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 https://github.com/cython/cython/issues/4585)

* ``__set_name__`` is called when assigning to class attributes.
  (Github issue https://github.com/cython/cython/issues/6179)

* Most builtin methods now provide their return type for type inference.
  (Github issues https://github.com/cython/cython/issues/4829, https://github.com/cython/cython/issues/5865, https://github.com/cython/cython/issues/6412)

* Method calls on builtin literal values are evaluated at compile time, if applicable.
  (Github issue https://github.com/cython/cython/issues/6383)

* The Python ``int`` type now maps directly to ``PyLong`` and is inferred accordingly.
  (Github issue https://github.com/cython/cython/issues/4237)

* Integer operations on known ``int`` types are faster.
  (Github issue https://github.com/cython/cython/issues/5785)

* f-strings are faster in some cases.
  (Github issues https://github.com/cython/cython/issues/5866, https://github.com/cython/cython/issues/6342, https://github.com/cython/cython/issues/6383)

* ``divmod()`` is faster on C ``int``.
  Patch by Tong He.  (Github issue https://github.com/cython/cython/issues/6073)

* ``dict.pop()`` is faster in some cases.
  (Github issue https://github.com/cython/cython/issues/5911)

* ``.isprintable()`` is optimised for Unicode characters.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6288)

* Constant (non-GC) Python objects are no longer traversed with ``Py_VISIT()`` during GC runs.
  (Github issue https://github.com/cython/cython/issues/6277)

* C++ classes implemented in Cython can now use method overloading.
  Patch by samaingw.  (Github issue https://github.com/cython/cython/issues/3235)

* Assigning a Python container to a C++ vector now makes use of ``__length_hint__``
  to avoid reallocations.
  Patch by Denis Lukianov.  (Github issue https://github.com/cython/cython/issues/6077)

* The C++11 ``emplace*`` methods were added to ``libcpp.deque``.
  Patch by Somin An.  (Github issue https://github.com/cython/cython/issues/6159)

* ``cpython.time`` was updated and extended for Python 3.13.
  (Github issue https://github.com/cython/cython/issues/6187)

* Dataclasses support the ``match_args`` option.
  (Github issue https://github.com/cython/cython/issues/5381)

* Threading in parallel sections can now be disabled with a new ``use_threads_if`` condition.
  (Github issue https://github.com/cython/cython/issues/5919)

* New options ``warn.deprecated.DEF`` and ``warn.deprecated.IF`` can silence the deprecation warnings.
  Patch by Eric Larson.  (Github issue https://github.com/cython/cython/issues/6243)

* ``cygdb`` shows more helpful output for some objects.
  Patch by Kent Slaney.  (Github issue https://github.com/cython/cython/issues/5958)

* Bazel build support for improved.
  Patch by mering.  (Github issue https://github.com/cython/cython/issues/6452)

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

Bugs fixed
----------

3.1.0 rc 2 (2025-05-07):

* 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 https://github.com/cython/cython/issues/6828)

* Functions with more than 10 constant default argument values could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6551)

* Naming a variable after its inferred type (e.g. `str += ""`) could trigger an infinite loop in Cython.
  (Github issue https://github.com/cython/cython/issues/6835)

* Cython is more relaxed about the exact C++ constructor name when it calls ``new()`` on ctypedefs.
  (Github issue https://github.com/cython/cython/issues/6821)

* Using ``cpp_locals`` in nogil sections could crash.
  (Github issue https://github.com/cython/cython/issues/6838)

* ``const struct`` declarations could lead to invalid assignments to ``const`` temp variables.
  (Github issue https://github.com/cython/cython/issues/6804)

* A refcounting error was fixed in the method class cell support code.
  (Github issue https://github.com/cython/cython/issues/6839)

3.1.0 rc 1 (2025-05-01):

* Iterating over literal sequences in generator expressions could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/6725)

* Tracing could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/6781)

* Non-ASCII function argument names could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/6813)

* Optimised ``divmod()`` calls could produce incorrect results in beta-1 due to incorrect C type usage.
  (Github issue https://github.com/cython/cython/issues/6786)

* Raising ``UnboundLocalError`` could fail for non-ascii variable names.
  (Github issue https://github.com/cython/cython/issues/6800)

* The signature of ``PyByteArray_Resize()`` in ``cpython.bytearray`` failed to propagate exceptions.
  Patch by Kirill Smelkov.  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6815)

3.1.0 beta 1 (2025-04-03):

* 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 https://github.com/cython/cython/issues/6578)

* ``PyDict_GetItemRef()`` and ``PyList_GetItemRef()`` were not always used correctly.
  Patch by Lisandro Dalcin.  (Github issue https://github.com/cython/cython/issues/6647)

* Inlined calls to local functions could crash with ``binding=False``.
  (Github issue https://github.com/cython/cython/issues/6556)

* Calling ``sorted()`` could crash in 3.1.0a1.
  (Github issue https://github.com/cython/cython/issues/6496)

* Calling 0-arg methods was unnecessarily slow in 3.1.0a1.
  (Github issue https://github.com/cython/cython/issues/6730)

* A crash when reading the interpreter ID was fixed.

* Crashes while tracing C function returns were resolved.
  (Github issue https://github.com/cython/cython/issues/6503)

* A compiler crash on ``complex/complex`` was resolved.
  (Github issue https://github.com/cython/cython/issues/6552)

* A compiler crash when using the ``cpp_locals`` directive was resolved.
  (Github issue https://github.com/cython/cython/issues/6370)

* Name mangling did not work correctly for attributes of extension types that have reserved C names.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6714)

* Cython's fake code objects are now compatible with GraalPython.
  (Github issue https://github.com/cython/cython/issues/6409)

* Stepping through foreign code with ``cygdb`` could fail with an ``IndexError``.
  Patch by clayote.  (Github issue https://github.com/cython/cython/issues/6552)

* Some PyPy incompatibilities were resolved.
  Patches by Matti Picus.  (Github issue https://github.com/cython/cython/issues/6592,  https://github.com/cython/cython/issues/6640)

* Interoperability with recent Pythran releases was fixed.
  (Github issue https://github.com/cython/cython/issues/6494)

* The ``gdb`` compatibility of ``cygdb`` was improved.
  Patch by Kent Slaney.  (Github issue https://github.com/cython/cython/issues/6681)

* Some redundant exception normalisation work was removed in Python 3.12+.
  (Github issue https://github.com/cython/cython/issues/6599)

* A compiler hang introduced in 3.1a1 when overriding methods was resolved.
  Patch by Aditya Pillai.  (Github issue https://github.com/cython/cython/issues/6704)

* A compiler crash was resolved when trying to issue a warning.
  Patch by Gabriele N. Tornetta.  (Github issue https://github.com/cython/cython/issues/6711)

* Some incomplete import time "safety checks" from 3.1.0a1 were removed again.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6726)

3.1.0 alpha 1 (2024-11-08):

* 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 https://github.com/cython/cython/issues/6366)

* Dataclasses did not handle default fields without init value correctly.
  (Github issue https://github.com/cython/cython/issues/5858)

* Implementing a special method based on another could lead to infinite recursion.
  (Github issue https://github.com/cython/cython/issues/5863)

* The ``__class__`` cell variable in methods was not always working as in Python.
  Initial patch by Tom Keefe.  (Github issue https://github.com/cython/cython/issues/2912)

* Lambda functions had no code objects. Their signature can now be introspected.
  (Github issue https://github.com/cython/cython/issues/2983)

* Subtyping `complex` as extension type could fail.
  (Github issue https://github.com/cython/cython/issues/6346)

* ``hasattr()`` now propagates exceptions that occur during lookup.
  (Github issue https://github.com/cython/cython/issues/6269)

* The base type of extension heap types is now traversed during GC runs in Py3.9+.
  (Github issue https://github.com/cython/cython/issues/4193)

* The Python ``&`` operator could touch invalid memory with certain ``0`` values in Python <= 3.10.
  Patch by Michael J. Sullivan.  (Github issue https://github.com/cython/cython/issues/4193)

* Exception values were not always recognised as equal at compile time.
  (Github issue https://github.com/cython/cython/issues/5709)

* Running Cython in different Python versions could generate slightly different C code
  due to differences in the builtins.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6355)

* File paths in the C code are now relative to the build directory.
  Patch by Oscar Benjamin.  (Github issue https://github.com/cython/cython/issues/6341)

* depfiles now use relative paths whenever possible.
  Patch by Loïc Estève.  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5760)

* Uselessly referring to C enums (not enum values) as Python objects is now rejected.
  Patch by Vyas Ramasubramani.  (Github issue https://github.com/cython/cython/issues/5638)

* Cython no longer acquires the GIL during in-place assignments to C attributes in nogil sections.
  Patch by Mads Ynddal.  (Github issue https://github.com/cython/cython/issues/6407)

* Several C++ warnings about ``char*`` casts were resolved.
  (Github issues https://github.com/cython/cython/issues/5515, https://github.com/cython/cython/issues/5847)

* C++ undefined behaviour was fixed in an error handling case.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5953)

* A crash was fixed when assigning a zero-length slice to a memoryview.
  Patch by Michael Man.  (Github issue https://github.com/cython/cython/issues/6227)

* Conditionally assigning to variables with the walrus operator could crash.
  (Github issue https://github.com/cython/cython/issues/6094)

* Unterminated string literals could lock up the build in an infinite loop.
  (Github issue https://github.com/cython/cython/issues/5977)

* Exporting C functions uses better platform compatible code.
  (Github issue https://github.com/cython/cython/issues/4683)

* The shebang in ``libpython.py`` was incorrect.
  Patch by Luke Hamburg.  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6354)

3.0.12 (2025-02-11):

* Release 3.0.11 introduced some incorrect ``noexcept`` warnings.
  (Github issue https://github.com/cython/cython/issues/6335)

* Conditional assignments to variables using the walrus operator could crash.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6328)

* In Py3, `pyximport` was not searching `sys.path` when looking for importable source files.
  (Github issue https://github.com/cython/cython/issues/5615)

* Using `& 0` on integers produced with `int.from_bytes()` could read invalid memory on Python 3.10.
  (Github issue https://github.com/cython/cython/issues/6480)

* Modules could fail to compile in PyPy 3.11 due to missing CPython specific header files.
  Patch by Matti Picus.  (Github issue https://github.com/cython/cython/issues/6482)

* Minor fix in C++ ``partial_sum()`` declaration.

3.0.11 (2024-08-05):

* The exception check value of functions declared in pxd files was not always applied in 3.0.10.
  (Github issue https://github.com/cython/cython/issues/6122)

* A crash on exception deallocations was fixed.
  (Github issue https://github.com/cython/cython/issues/6022)

* A crash was fixed when assigning a zero-length slice to a memoryview.
  Patch by Michael Man.  (Github issue https://github.com/cython/cython/issues/6227)

* ``libcpp.optional.value()`` could crash if it raised a C++ exception.
  Patch by Alexander Condello.  (Github issue https://github.com/cython/cython/issues/6190)

* The return type of ``str()`` was mishandled, leading to crashes with ``language_level=3``.
  (Github issue https://github.com/cython/cython/issues/6166)

* ``bytes.startswith/endswith()`` failed for non-bytes substrings (e.g. ``bytearray``).
  (Github issue https://github.com/cython/cython/issues/6168)

* Fused ctuples crashed Cython.
  (Github issue https://github.com/cython/cython/issues/6068)

* A compiler crash was fixed when using extension types in fused types.
  (Github issue https://github.com/cython/cython/issues/6204)

* The module cleanup code was incorrect for globally defined memory view slices.
  (Github issue https://github.com/cython/cython/issues/6276)

* Some adaptations were made to enable compilation in Python 3.13.
  (Github issues https://github.com/cython/cython/issues/5997, https://github.com/cython/cython/issues/6182, https://github.com/cython/cython/issues/6251)

Other changes
-------------

3.1.0 rc 1 (2025-05-01):

* 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(TheUserEnumClass.__members__)``.
  Anonymous enums still produce global item names, as before.
  (Github issue https://github.com/cython/cython/issues/4571)

3.1.0 beta 1 (2025-04-03):

* All Cython-internal types (functions, coroutines, …) are now heap types and use type specs.
  (Github issue https://github.com/cython/cython/issues/6633)

* Tracing/monitoring is now disabled in parallel/prange sections.
  (Github issue https://github.com/cython/cython/issues/6709)

* The ``numpy.math`` cimport module has been deprecated.
  Usages should be replaced by ``libc.math``.
  (Github issue https://github.com/cython/cython/issues/6743)

* Includes all fixes as of Cython 3.0.12.

3.1.0 alpha 1 (2024-11-08):

* Support for Python 2.7 - 3.7 was removed, along with large chunks of legacy code.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5827)

* The Py2 types ``unicode`` and ``basestring`` are now deprecated and have become aliases
  of the ``str`` type.
  (Github issue https://github.com/cython/cython/issues/6374)

* Docstrings now strip their leading whitespace according to PEP-257.
  Patch by Lawrence Mitchell.  (Github issue https://github.com/cython/cython/issues/6241)

* Type checkers should have it easier to find and validate Cython types in .py files.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5842)

* Usages of the outdated ``WITH_THREAD`` macro guard were removed.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6036)

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

3.1.0 (2025-05-08)

==================

* No functional changes since 3.1.0rc2.

Features added
--------------

3.1.0 rc 2 (2025-05-07):

* 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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6842)

3.1.0 rc 1 (2025-05-01):

* ``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 https://github.com/cython/cython/issues/6579)

* A new directive ``subinterpreters_compatible=shared_gil/own_gil`` was added to allow modules
  to declare support for subinterpreters.
  (Github issue https://github.com/cython/cython/issues/6513)

* ``divmod()`` is also optimised for C floating point types and can be called on C number types
  without holding the GIL.
  (Github issue https://github.com/cython/cython/issues/6801)

* New C++ declarations were added.
  (Github issues https://github.com/cython/cython/issues/6625, https://github.com/cython/cython/issues/6731)

* ``embedsignature`` now works for special methods (if they have a docstring).
  (Github issue https://github.com/cython/cython/issues/1577)

3.1.0 beta 1 (2025-04-03):

* Global ``cdef const …`` variables are supported.
  (Github issue https://github.com/cython/cython/issues/6542)

* A new context manager / function decorator ``cython.critical_section`` was added
  wrapping Python's critical section C-API feature.
  (Github issues https://github.com/cython/cython/issues/6516, https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/2356)

* The type of ``prange`` loop targets is now inferred.
  (Github issue https://github.com/cython/cython/issues/6585)

* Extracting keyword arguments is faster in some cases.
  (Github issue https://github.com/cython/cython/issues/6683)

* Calling ``divmod()``on any C integer types is efficient.
  (Github issue https://github.com/cython/cython/issues/6717)

* Some async/coroutine/vectorcall code has improved fast-paths.
  (Github issues https://github.com/cython/cython/issues/6732, https://github.com/cython/cython/issues/6735, https://github.com/cython/cython/issues/6736, https://github.com/cython/cython/issues/6738, https://github.com/cython/cython/issues/6742, https://github.com/cython/cython/issues/6771)

* Calls to Python builtins and extension types use the vectorcall protocol.
  (Github issue https://github.com/cython/cython/issues/6744)

* Method calls use ``PyObject_VectorcallMethod()`` where possible.
  (Github issue https://github.com/cython/cython/issues/6747)

* Some C-API shortcuts were (re-)added.
  (Github issue https://github.com/cython/cython/issues/6761)

* Cython can avoid normalising exceptions in an `except` clause if it knows that they are unused.
  (Github issue https://github.com/cython/cython/issues/6601)

* The ``cython`` command has a new option ``--cache`` to cache generated files.
  (Github issue https://github.com/cython/cython/issues/6091)

* The ``cythonize`` command has a new option ``--timeit`` to benchmark Cython code snippets.
  (Github issue https://github.com/cython/cython/issues/6697)

* The argument parsing ``cygdb`` command was improved based on ``argparse``.
  Patch by William Ayd.  (Github issue https://github.com/cython/cython/issues/5499)

* The ``PyWeakref_GetRef`` declaration was added to ``cpython.weakref`` and backported.
  Patch by Lysandros Nikolaou.  (Github issue https://github.com/cython/cython/issues/6478)

* ``std::span`` declarations were added to ``libcpp``.
  Patch by Alexander Condello.  (Github issue https://github.com/cython/cython/issues/6539)

* ``std::string_view`` declarations were added to ``libcpp``.
  Patch by Antoine Pitrou.  (Github issue https://github.com/cython/cython/issues/6539)

* Mutex declarations for ``libc`` and  ``libcpp`` were added.
  (Github issue https://github.com/cython/cython/issues/6610)

* Several C++ declarations were improved and extended.
  Patches by Yury V. Zaytsev.  (Github issues https://github.com/cython/cython/issues/488, https://github.com/cython/cython/issues/489)

* Bazel build rules were updated for better interoperability.
  Patch by maleo.  (Github issue https://github.com/cython/cython/issues/6478)

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

3.1.0 alpha 1 (2024-11-08):

* 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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5955, https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6254)

* ``cython.const[]`` and ``cython.volatile[]`` are now available as type modifiers in Python code.
  (Github issue https://github.com/cython/cython/issues/5728)

* ``cython.pointer[SomeCType]`` can now be used to define pointer types in Python type annotations.
  (Github issue https://github.com/cython/cython/issues/5071)

* Several improvements were made to reduce the size of the resulting extension modules.
  (Github issue https://github.com/cython/cython/issues/4425)

* Function calls now use the PEP-590 Vectorcall protocol, even when passing keyword arguments.
  (Github issues https://github.com/cython/cython/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 https://github.com/cython/cython/issues/4585)

* ``__set_name__`` is called when assigning to class attributes.
  (Github issue https://github.com/cython/cython/issues/6179)

* Most builtin methods now provide their return type for type inference.
  (Github issues https://github.com/cython/cython/issues/4829, https://github.com/cython/cython/issues/5865, https://github.com/cython/cython/issues/6412)

* Method calls on builtin literal values are evaluated at compile time, if applicable.
  (Github issue https://github.com/cython/cython/issues/6383)

* The Python ``int`` type now maps directly to ``PyLong`` and is inferred accordingly.
  (Github issue https://github.com/cython/cython/issues/4237)

* Integer operations on known ``int`` types are faster.
  (Github issue https://github.com/cython/cython/issues/5785)

* f-strings are faster in some cases.
  (Github issues https://github.com/cython/cython/issues/5866, https://github.com/cython/cython/issues/6342, https://github.com/cython/cython/issues/6383)

* ``divmod()`` is faster on C ``int``.
  Patch by Tong He.  (Github issue https://github.com/cython/cython/issues/6073)

* ``dict.pop()`` is faster in some cases.
  (Github issue https://github.com/cython/cython/issues/5911)

* ``.isprintable()`` is optimised for Unicode characters.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6288)

* Constant (non-GC) Python objects are no longer traversed with ``Py_VISIT()`` during GC runs.
  (Github issue https://github.com/cython/cython/issues/6277)

* C++ classes implemented in Cython can now use method overloading.
  Patch by samaingw.  (Github issue https://github.com/cython/cython/issues/3235)

* Assigning a Python container to a C++ vector now makes use of ``__length_hint__``
  to avoid reallocations.
  Patch by Denis Lukianov.  (Github issue https://github.com/cython/cython/issues/6077)

* The C++11 ``emplace*`` methods were added to ``libcpp.deque``.
  Patch by Somin An.  (Github issue https://github.com/cython/cython/issues/6159)

* ``cpython.time`` was updated and extended for Python 3.13.
  (Github issue https://github.com/cython/cython/issues/6187)

* Dataclasses support the ``match_args`` option.
  (Github issue https://github.com/cython/cython/issues/5381)

* Threading in parallel sections can now be disabled with a new ``use_threads_if`` condition.
  (Github issue https://github.com/cython/cython/issues/5919)

* New options ``warn.deprecated.DEF`` and ``warn.deprecated.IF`` can silence the deprecation warnings.
  Patch by Eric Larson.  (Github issue https://github.com/cython/cython/issues/6243)

* ``cygdb`` shows more helpful output for some objects.
  Patch by Kent Slaney.  (Github issue https://github.com/cython/cython/issues/5958)

* Bazel build support for improved.
  Patch by mering.  (Github issue https://github.com/cython/cython/issues/6452)

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

Bugs fixed
----------

3.1.0 rc 2 (2025-05-07):

* 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 https://github.com/cython/cython/issues/6828)

* Functions with more than 10 constant default argument values could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6551)

* Naming a variable after its inferred type (e.g. `str += ""`) could trigger an infinite loop in Cython.
  (Github issue https://github.com/cython/cython/issues/6835)

* Cython is more relaxed about the exact C++ constructor name when it calls ``new()`` on ctypedefs.
  (Github issue https://github.com/cython/cython/issues/6821)

* Using ``cpp_locals`` in nogil sections could crash.
  (Github issue https://github.com/cython/cython/issues/6838)

* ``const struct`` declarations could lead to invalid assignments to ``const`` temp variables.
  (Github issue https://github.com/cython/cython/issues/6804)

* A refcounting error was fixed in the method class cell support code.
  (Github issue https://github.com/cython/cython/issues/6839)

3.1.0 rc 1 (2025-05-01):

* Iterating over literal sequences in generator expressions could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/6725)

* Tracing could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/6781)

* Non-ASCII function argument names could generate invalid C code.
  (Github issue https://github.com/cython/cython/issues/6813)

* Optimised ``divmod()`` calls could produce incorrect results in beta-1 due to incorrect C type usage.
  (Github issue https://github.com/cython/cython/issues/6786)

* Raising ``UnboundLocalError`` could fail for non-ascii variable names.
  (Github issue https://github.com/cython/cython/issues/6800)

* The signature of ``PyByteArray_Resize()`` in ``cpython.bytearray`` failed to propagate exceptions.
  Patch by Kirill Smelkov.  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6815)

3.1.0 beta 1 (2025-04-03):

* 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 https://github.com/cython/cython/issues/6578)

* ``PyDict_GetItemRef()`` and ``PyList_GetItemRef()`` were not always used correctly.
  Patch by Lisandro Dalcin.  (Github issue https://github.com/cython/cython/issues/6647)

* Inlined calls to local functions could crash with ``binding=False``.
  (Github issue https://github.com/cython/cython/issues/6556)

* Calling ``sorted()`` could crash in 3.1.0a1.
  (Github issue https://github.com/cython/cython/issues/6496)

* Calling 0-arg methods was unnecessarily slow in 3.1.0a1.
  (Github issue https://github.com/cython/cython/issues/6730)

* A crash when reading the interpreter ID was fixed.

* Crashes while tracing C function returns were resolved.
  (Github issue https://github.com/cython/cython/issues/6503)

* A compiler crash on ``complex/complex`` was resolved.
  (Github issue https://github.com/cython/cython/issues/6552)

* A compiler crash when using the ``cpp_locals`` directive was resolved.
  (Github issue https://github.com/cython/cython/issues/6370)

* Name mangling did not work correctly for attributes of extension types that have reserved C names.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6714)

* Cython's fake code objects are now compatible with GraalPython.
  (Github issue https://github.com/cython/cython/issues/6409)

* Stepping through foreign code with ``cygdb`` could fail with an ``IndexError``.
  Patch by clayote.  (Github issue https://github.com/cython/cython/issues/6552)

* Some PyPy incompatibilities were resolved.
  Patches by Matti Picus.  (Github issue https://github.com/cython/cython/issues/6592,  https://github.com/cython/cython/issues/6640)

* Interoperability with recent Pythran releases was fixed.
  (Github issue https://github.com/cython/cython/issues/6494)

* The ``gdb`` compatibility of ``cygdb`` was improved.
  Patch by Kent Slaney.  (Github issue https://github.com/cython/cython/issues/6681)

* Some redundant exception normalisation work was removed in Python 3.12+.
  (Github issue https://github.com/cython/cython/issues/6599)

* A compiler hang introduced in 3.1a1 when overriding methods was resolved.
  Patch by Aditya Pillai.  (Github issue https://github.com/cython/cython/issues/6704)

* A compiler crash was resolved when trying to issue a warning.
  Patch by Gabriele N. Tornetta.  (Github issue https://github.com/cython/cython/issues/6711)

* Some incomplete import time "safety checks" from 3.1.0a1 were removed again.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6726)

3.1.0 alpha 1 (2024-11-08):

* 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 https://github.com/cython/cython/issues/6366)

* Dataclasses did not handle default fields without init value correctly.
  (Github issue https://github.com/cython/cython/issues/5858)

* Implementing a special method based on another could lead to infinite recursion.
  (Github issue https://github.com/cython/cython/issues/5863)

* The ``__class__`` cell variable in methods was not always working as in Python.
  Initial patch by Tom Keefe.  (Github issue https://github.com/cython/cython/issues/2912)

* Lambda functions had no code objects. Their signature can now be introspected.
  (Github issue https://github.com/cython/cython/issues/2983)

* Subtyping `complex` as extension type could fail.
  (Github issue https://github.com/cython/cython/issues/6346)

* ``hasattr()`` now propagates exceptions that occur during lookup.
  (Github issue https://github.com/cython/cython/issues/6269)

* The base type of extension heap types is now traversed during GC runs in Py3.9+.
  (Github issue https://github.com/cython/cython/issues/4193)

* The Python ``&`` operator could touch invalid memory with certain ``0`` values in Python <= 3.10.
  Patch by Michael J. Sullivan.  (Github issue https://github.com/cython/cython/issues/4193)

* Exception values were not always recognised as equal at compile time.
  (Github issue https://github.com/cython/cython/issues/5709)

* Running Cython in different Python versions could generate slightly different C code
  due to differences in the builtins.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6355)

* File paths in the C code are now relative to the build directory.
  Patch by Oscar Benjamin.  (Github issue https://github.com/cython/cython/issues/6341)

* depfiles now use relative paths whenever possible.
  Patch by Loïc Estève.  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5760)

* Uselessly referring to C enums (not enum values) as Python objects is now rejected.
  Patch by Vyas Ramasubramani.  (Github issue https://github.com/cython/cython/issues/5638)

* Cython no longer acquires the GIL during in-place assignments to C attributes in nogil sections.
  Patch by Mads Ynddal.  (Github issue https://github.com/cython/cython/issues/6407)

* Several C++ warnings about ``char*`` casts were resolved.
  (Github issues https://github.com/cython/cython/issues/5515, https://github.com/cython/cython/issues/5847)

* C++ undefined behaviour was fixed in an error handling case.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5953)

* A crash was fixed when assigning a zero-length slice to a memoryview.
  Patch by Michael Man.  (Github issue https://github.com/cython/cython/issues/6227)

* Conditionally assigning to variables with the walrus operator could crash.
  (Github issue https://github.com/cython/cython/issues/6094)

* Unterminated string literals could lock up the build in an infinite loop.
  (Github issue https://github.com/cython/cython/issues/5977)

* Exporting C functions uses better platform compatible code.
  (Github issue https://github.com/cython/cython/issues/4683)

* The shebang in ``libpython.py`` was incorrect.
  Patch by Luke Hamburg.  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6354)

3.0.12 (2025-02-11):

* Release 3.0.11 introduced some incorrect ``noexcept`` warnings.
  (Github issue https://github.com/cython/cython/issues/6335)

* Conditional assignments to variables using the walrus operator could crash.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6328)

* In Py3, `pyximport` was not searching `sys.path` when looking for importable source files.
  (Github issue https://github.com/cython/cython/issues/5615)

* Using `& 0` on integers produced with `int.from_bytes()` could read invalid memory on Python 3.10.
  (Github issue https://github.com/cython/cython/issues/6480)

* Modules could fail to compile in PyPy 3.11 due to missing CPython specific header files.
  Patch by Matti Picus.  (Github issue https://github.com/cython/cython/issues/6482)

* Minor fix in C++ ``partial_sum()`` declaration.

3.0.11 (2024-08-05):

* The exception check value of functions declared in pxd files was not always applied in 3.0.10.
  (Github issue https://github.com/cython/cython/issues/6122)

* A crash on exception deallocations was fixed.
  (Github issue https://github.com/cython/cython/issues/6022)

* A crash was fixed when assigning a zero-length slice to a memoryview.
  Patch by Michael Man.  (Github issue https://github.com/cython/cython/issues/6227)

* ``libcpp.optional.value()`` could crash if it raised a C++ exception.
  Patch by Alexander Condello.  (Github issue https://github.com/cython/cython/issues/6190)

* The return type of ``str()`` was mishandled, leading to crashes with ``language_level=3``.
  (Github issue https://github.com/cython/cython/issues/6166)

* ``bytes.startswith/endswith()`` failed for non-bytes substrings (e.g. ``bytearray``).
  (Github issue https://github.com/cython/cython/issues/6168)

* Fused ctuples crashed Cython.
  (Github issue https://github.com/cython/cython/issues/6068)

* A compiler crash was fixed when using extension types in fused types.
  (Github issue https://github.com/cython/cython/issues/6204)

* The module cleanup code was incorrect for globally defined memory view slices.
  (Github issue https://github.com/cython/cython/issues/6276)

* Some adaptations were made to enable compilation in Python 3.13.
  (Github issues https://github.com/cython/cython/issues/5997, https://github.com/cython/cython/issues/6182, https://github.com/cython/cython/issues/6251)

Other changes
-------------

3.1.0 rc 1 (2025-05-01):

* 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(TheUserEnumClass.__members__)``.
  Anonymous enums still produce global item names, as before.
  (Github issue https://github.com/cython/cython/issues/4571)

3.1.0 beta 1 (2025-04-03):

* All Cython-internal types (functions, coroutines, …) are now heap types and use type specs.
  (Github issue https://github.com/cython/cython/issues/6633)

* Tracing/monitoring is now disabled in parallel/prange sections.
  (Github issue https://github.com/cython/cython/issues/6709)

* The ``numpy.math`` cimport module has been deprecated.
  Usages should be replaced by ``libc.math``.
  (Github issue https://github.com/cython/cython/issues/6743)

* Includes all fixes as of Cython 3.0.12.

3.1.0 alpha 1 (2024-11-08):

* Support for Python 2.7 - 3.7 was removed, along with large chunks of legacy code.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5827)

* The Py2 types ``unicode`` and ``basestring`` are now deprecated and have become aliases
  of the ``str`` type.
  (Github issue https://github.com/cython/cython/issues/6374)

* Docstrings now strip their leading whitespace according to PEP-257.
  Patch by Lawrence Mitchell.  (Github issue https://github.com/cython/cython/issues/6241)

* Type checkers should have it easier to find and validate Cython types in .py files.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/5842)

* Usages of the outdated ``WITH_THREAD`` macro guard were removed.
  (Github issue https://github.com/cython/cython/issues/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 https://github.com/cython/cython/issues/6036)

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

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 :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 :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 :issue:`6828`)

* Functions with more than 10 constant default argument values could generate invalid C code.
  (Github issue :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 :issue:`6551`)

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

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

* Using ``cpp_locals`` in nogil sections could crash.
  (Github issue :issue:`6838`)

* ``const struct`` declarations could lead to invalid assignments to ``const`` temp variables.
  (Github issue :issue:`6804`)

* A refcounting error was fixed in the method class cell support code.
  (Github issue :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 :issue:`6579`)

* A new directive ``subinterpreters_compatible=shared_gil/own_gil`` was added to allow modules
  to declare support for subinterpreters.
  (Github issue :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 :issue:`6801`)

* New C++ declarations were added.
  (Github issues :issue:`6625`, :issue:`6731`)

* ``embedsignature`` now works for special methods (if they have a docstring).
  (Github issue :issue:`1577`)

Bugs fixed
----------

* Iterating over literal sequences in generator expressions could generate invalid C code.
  (Github issue :issue:`6725`)

* Tracing could generate invalid C code.
  (Github issue :issue:`6781`)

* Non-ASCII function argument names could generate invalid C code.
  (Github issue :issue:`6813`)

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

* Raising ``UnboundLocalError`` could fail for non-ascii variable names.
  (Github issue :issue:`6800`)

* The signature of ``PyByteArray_Resize()`` in ``cpython.bytearray`` failed to propagate exceptions.
  Patch by Kirill Smelkov.  (Github issue :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 :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(TheUserEnumClass.__members__)``.
  Anonymous enums still produce global item names, as before.
  (Github issue :issue:`4571`)

3.1.0 beta 1 (2025-04-03)

==========================

Features added
--------------

* Global ``cdef const …`` variables are supported.
  (Github issue :issue:`6542`)

* A new context manager / function decorator ``cython.critical_section`` was added
  wrapping Python's critical section C-API feature.
  (Github issues :issue:`6516`, :issue:`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 :issue:`2356`)

* The type of ``prange`` loop targets is now inferred.
  (Github issue :issue:`6585`)

* Extracting keyword arguments is faster in some cases.
  (Github issue :issue:`6683`)

* Calling ``divmod()``on any C integer types is efficient.
  (Github issue :issue:`6717`)

* Some async/coroutine/vectorcall code has improved fast-paths.
  (Github issues :issue:`6732`, :issue:`6735`, :issue:`6736`, :issue:`6738`, :issue:`6742`, :issue:`6771`)

* Calls to Python builtins and extension types use the vectorcall protocol.
  (Github issue :issue:`6744`)

* Method calls use ``PyObject_VectorcallMethod()`` where possible.
  (Github issue :issue:`6747`)

* Some C-API shortcuts were (re-)added.
  (Github issue :issue:`6761`)

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

* The ``cython`` command has a new option ``--cache`` to cache generated files.
  (Github issue :issue:`6091`)

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

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

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

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

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

* Mutex declarations for ``libc`` and  ``libcpp`` were added.
  (Github issue :issue:`6610`)

* Several C++ declarations were improved and extended.
  Patches by Yury V. Zaytsev.  (Github issues :issue:`488`, :issue:`489`)

* Bazel build rules were updated for better interoperability.
  Patch by maleo.  (Github issue :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 :issue:`6578`)

* ``PyDict_GetItemRef()`` and ``PyList_GetItemRef()`` were not always used correctly.
  Patch by Lisandro Dalcin.  (Github issue :issue:`6647`)

* Inlined calls to local functions could crash with ``binding=False``.
  (Github issue :issue:`6556`)

* Calling ``sorted()`` could crash in 3.1.0a1.
  (Github issue :issue:`6496`)

* Calling 0-arg methods was unnecessarily slow in 3.1.0a1.
  (Github issue :issue:`6730`)

* A crash when reading the interpreter ID was fixed.

* Crashes while tracing C function returns were resolved.
  (Github issue :issue:`6503`)

* A compiler crash on ``complex/complex`` was resolved.
  (Github issue :issue:`6552`)

* A compiler crash when using the ``cpp_locals`` directive was resolved.
  (Github issue :issue:`6370`)

* Name mangling did not work correctly for attributes of extension types that have reserved C names.
  (Github issue :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 :issue:`6714`)

* Cython's fake code objects are now compatible with GraalPython.
  (Github issue :issue:`6409`)

* Stepping through foreign code with ``cygdb`` could fail with an ``IndexError``.
  Patch by clayote.  (Github issue :issue:`6552`)

* Some PyPy incompatibilities were resolved.
  Patches by Matti Picus.  (Github issue :issue:`6592`,  :issue:`6640`)

* Interoperability with recent Pythran releases was fixed.
  (Github issue :issue:`6494`)

* The ``gdb`` compatibility of ``cygdb`` was improved.
  Patch by Kent Slaney.  (Github issue :issue:`6681`)

* Some redundant exception normalisation work was removed in Python 3.12+.
  (Github issue :issue:`6599`)

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

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

* Some incomplete import time "safety checks" from 3.1.0a1 were removed again.
  (Github issue :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 :issue:`6726`)

Other changes
-------------

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

* Tracing/monitoring is now disabled in parallel/prange sections.
  (Github issue :issue:`6709`)

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

* Includes all fixes as of Cython 3.0.12.

3.0.12 (2025-02-11)

===================

Bugs fixed
----------

* Release 3.0.11 introduced some incorrect ``noexcept`` warnings.
  (Github issue :issue:`6335`)

* Conditional assignments to variables using the walrus operator could crash.
  (Github issue :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 :issue:`6328`)

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

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

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

* Minor fix in C++ ``partial_sum()`` declaration.