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 :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 :issue:`7183`)

3.2.0b1 (2025-10-22)

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

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

* Builtin exception types are now inferred.
  (Github issue :issue:`6908`)

* The list of known, inferred and optimised Python builtins was updated.
  `range` is now considered a type. `ascii`, `bin`, `format`, `hex`, `oct` were added as functions.
  (Github issue :issue:`6931`)

* The f-string syntax was extended according to PEP-701.
  (Github issue :issue:`5452`)

* t-strings are implemented according to PEP-750.  The implementation backports the template classes
  but prefers existing backports if installed separately.
  (Github issue :issue:`6811`)

* Unknown return type annotations with `->` are no longer rejected but produce warnings.
  This allows better integration with Python type hints that are not always usable for Cython.
  ``-> None``  is also allowed now.
  Patch by jpe.  (Github issue :issue:`6946`)

* The runtime Python dispatch for fused functions is substantially faster.
  (Github issues :issue:`1385`, :issue:`6996`)

* Freelists (via cdef class decorator and for internally used types such as ``async``)
  are now also used in the Limited API and with extension type specs enabled.
  (Github issue :issue:`7151`)

* Module imports now quickly check for an already imported module to speed up reimports.
  Patch by Lysandros Nikolaou.  (Github issue :issue:`7035`)

* Type checks on PEP-604 union types (`int | None`) are optimised into separate checks.
  (Github issue :issue:`6935`)

* Assignments to the PEP-604 union type `float | None` allow any suitable Python number as input
  and convert it to a Python `float` automatically.
  (Github issue :issue:`5750`)

* Item type inference was improved for looping over literals.
  (Github issue :issue:`6912`)

* Looping over literal sequences and strings now uses efficient C array looping if possible.
  (Github issue :issue:`6926`)

* Releasing the GIL from an unknown lock state is more efficient.
  (Github issue :issue:`6847`)

* ``cython.critical_section(PyMutex)`` now works, as with Python objects.
  (Github issue :issue:`6847`)

* ``bool(c_int/float/ptr)`` avoid passing through Python objects.
  (Github issue :issue:`7015`)

* Variables assigned inside of ``prange`` loops can now be initialised outside of the loop.
  (Github issue :issue:`7178`)

* Unused exceptions in ``except`` clauses are detected in some more cases to avoid their normalisation.
  (Github issue :issue:`7021`)

* Mixed operations on C integers with Python ints use less code and are more streamlined for Py3.12+.
  (Github issue :issue:`7244`)

* Some object constants are now marked as ``immortal`` to speed up their reference counting
  in recent CPython versions.  This can be configured with the ``CYTHON_IMMORTAL_CONSTANTS`` C macro.
  (Github issue :issue:`7118`)

* Further improvements were made to reduce the size of the resulting extension modules.
  (Github issue :issue:`6983`, :issue:`7199`, :issue:`7220`, :issue:`7238`)

* Several improvements were made in freethreaded Python code.
  (Github issues :issue:`6936`, :issue:`6939`, :issue:`6949`, :issue:`6984`,
   :issue:`7011`, :issue:`7066`, :issue:`7114`, :issue:`7200`)

* Several improvements were made for the Limited API.
  (Github issues :issue:`6959`, :issue:`6991`)

* Several improvements were made for the GraalPython support.
  Patch by Michael Šimáček.  (Github issue :issue:`7074`)

* Some GIL-safe C-API wrappers were added to the libc/libcpp declarations.
  (Github issue :issue:`6829`, :issue:`6993`)

* String and number constants use less storage space in the module.
  (Github issues :issue:`6971`, :issue:`6978`, :issue:`6986`)

* The managed dict/weakref support in CPython 3.12+ is used for internal types
  to benefit from future CPython optimisations here.
  (Github issue :issue:`6891`)

* Using ``NaN`` as exception return value is supported.
  (Github issues :issue:`6900`, :issue:`6903`)

* Declarations for C++ condition variables were added.
  (Github issue :issue:`6836`)

* The annotated source HTML page shows alternating +/− markers to open/close lines.
  Patch by Kamil Monicz.  (Github issue :issue:`7099`)

* ``cython --embed`` gained a new option ``--embed-modules=…`` to list further extension modules
  that will be statically linked into the generated extension module, to get them initialised
  on application start.
  (Github issue :issue:`2849`)

* The ``setup.py`` script of Cython now allows passing the desired Limited API version
  like ``--cython-limited-api=3.11``.
  (Github issue :issue:`7228`)

* Unicode 16.0.0 is used to parse identifiers.
  (Github issue :issue:`6836`)

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

* Special float exception values could generate invalid C code.
  (Github issues :issue:`6900`, :issue:`6903`)

* References to the Python ``bool`` type could generate invalid C code.
  (Github issue :issue:`6902`)

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

* Vectorcalls could use needless temp assignments for ``self``.
  (Github issue :issue:`6909`)

* Iterating over temporary memoryviews could crash Cython.
  (Github issue :issue:`7005`)

* Type casts on constants as part of numeric expressions could crash Cython.
  (Github issue :issue:`6779`)

* Long code bodies in ``with`` statements could crash Cython.
  (Github issue :issue:`7122`)

* Indexing ``bytes`` failed to optimise in some cases.
  (Github issue :issue:`6997`)

* Optimised C integer formatting in f-strings failed to apply to typedef types.
  (Github issue :issue:`7170`)

* In auto-pickling, trying to unpickle an object that has no ``__dict__`` from object pickle data
  that includes instance dict state is now an error.
  (Github issue :issue:`7222`)

* The type objects of heap types were not always correctly decrefed on deallocation.
  (Github issue :issue:`7145`)

* Pure mode type aliases like ``p_int`` or ``ulong`` leaked into some C type contexts,
  risking to conflict with user declarations.
  (Github issues :issue:`6922`, :issue:`6339`)

* Boolean (emptyness) tests on builtin containers could fail to handle (unlikely) errors.
  (Github issue :issue:`7090`)

* The return type of ``bytes.join()`` was sometimes inferred as plain ``object``.
  (Github issue :issue:`6987`)

* Type inference could fail to understand ``prange()`` arguments.
  (Github issue :issue:`6974`)

* ``embedsignatures`` failed if ``lambda`` was used in function default arguments.
  (Github issue :issue:`6880`)

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

* ``PyType_FromModuleAndSpec`` was incorrectly used in Limited API code before Py3.10.
  (Github issue :issue:`7181`)

* Conversion code for memoryview dtypes from and to Python objects generated C warnings about
  incorrect ``const`` / non-``const``  casting code.
  (Github issue :issue:`7219`)

* ``cythonize`` (program and function) now uses :class:`concurrent.futures.ProcessPoolExecutor`
  instead of :class:`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 :issue:`7183`)

* Cython's tools and frontend scripts now use ``python3``  instead of just ``python``
  in their shebang line.
  Patch by Matti Picus.  (Github issue :issue:`7053`)

* The ``setup.py`` script in the ``Demos/`` subdirectory failed to build.
  (Github issue :issue:`7228`)

* Includes all fixes as of Cython 3.1.5.

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

* Usages of `Py_TPFLAGS_HAVE_FINALIZE` were removed.  The constant remains available as cimport from
  ``cpython.object`` for legacy reasons.
  (Github issue :issue:`6423`)

3.2.0b1 (2025-10-22)

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

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

* Builtin exception types are now inferred.
  (Github issue :issue:`6908`)

* The list of known, inferred and optimised Python builtins was updated.
  `range` is now considered a type. `ascii`, `bin`, `format`, `hex`, `oct` were added as functions.
  (Github issue :issue:`6931`)

* The f-string syntax was extended according to PEP-701.
  (Github issue :issue:`5452`)

* t-strings are implemented according to PEP-750.  The implementation backports the template classes
  but prefers existing backports if installed separately.
  (Github issue :issue:`6811`)

* Unknown return type annotations with `->` are no longer rejected but produce warnings.
  This allows better integration with Python type hints that are not always usable for Cython.
  ``-> None``  is also allowed now.
  Patch by jpe.  (Github issue :issue:`6946`)

* The runtime Python dispatch for fused functions is substantially faster.
  (Github issues :issue:`1385`, :issue:`6996`)

* Freelists (via cdef class decorator and for internally used types such as ``async``)
  are now also used in the Limited API and with extension type specs enabled.
  (Github issue :issue:`7151`)

* Module imports now quickly check for an already imported module to speed up reimports.
  Patch by Lysandros Nikolaou.  (Github issue :issue:`7035`)

* Type checks on PEP-604 union types (`int | None`) are optimised into separate checks.
  (Github issue :issue:`6935`)

* Assignments to the PEP-604 union type `float | None` allow any suitable Python number as input
  and convert it to a Python `float` automatically.
  (Github issue :issue:`5750`)

* Item type inference was improved for looping over literals.
  (Github issue :issue:`6912`)

* Looping over literal sequences and strings now uses efficient C array looping if possible.
  (Github issue :issue:`6926`)

* Releasing the GIL from an unknown lock state is more efficient.
  (Github issue :issue:`6847`)

* ``cython.critical_section(PyMutex)`` now works, as with Python objects.
  (Github issue :issue:`6847`)

* ``bool(c_int/float/ptr)`` avoid passing through Python objects.
  (Github issue :issue:`7015`)

* Variables assigned inside of ``prange`` loops can now be initialised outside of the loop.
  (Github issue :issue:`7178`)

* Unused exceptions in ``except`` clauses are detected in some more cases to avoid their normalisation.
  (Github issue :issue:`7021`)

* Mixed operations on C integers with Python ints use less code and are more streamlined for Py3.12+.
  (Github issue :issue:`7244`)

* Some object constants are now marked as ``immortal`` to speed up their reference counting
  in recent CPython versions.  This can be configured with the ``CYTHON_IMMORTAL_CONSTANTS`` C macro.
  (Github issue :issue:`7118`)

* Further improvements were made to reduce the size of the resulting extension modules.
  (Github issue :issue:`6983`, :issue:`7199`, :issue:`7220`, :issue:`7238`)

* Several improvements were made in freethreaded Python code.
  (Github issues :issue:`6936`, :issue:`6939`, :issue:`6949`, :issue:`6984`,
  :issue:`7011`, :issue:`7066`, :issue:`7114`, :issue:`7200`)

* Several improvements were made for the Limited API.
  (Github issues :issue:`6959`, :issue:`6991`)

* Several improvements were made for the GraalPython support.
  Patch by Michael Šimáček.  (Github issue :issue:`7074`)

* Some GIL-safe C-API wrappers were added to the libc/libcpp declarations.
  (Github issue :issue:`6829`, :issue:`6993`)

* String and number constants use less storage space in the module.
  (Github issues :issue:`6971`, :issue:`6978`, :issue:`6986`)

* The managed dict/weakref support in CPython 3.12+ is used for internal types
  to benefit from future CPython optimisations here.
  (Github issue :issue:`6891`)

* Using ``NaN`` as exception return value is supported.
  (Github issues :issue:`6900`, :issue:`6903`)

* Declarations for C++ condition variables were added.
  (Github issue :issue:`6836`)

* The annotated source HTML page shows alternating +/− markers to open/close lines.
  Patch by Kamil Monicz.  (Github issue :issue:`7099`)

* ``cython --embed`` gained a new option ``--embed-modules=…`` to list further extension modules
  that will be statically linked into the generated extension module, to get them initialised
  on application start.
  (Github issue :issue:`2849`)

* The ``setup.py`` script of Cython now allows passing the desired Limited API version
  like ``--cython-limited-api=3.11``.
  (Github issue :issue:`7228`)

* Unicode 16.0.0 is used to parse identifiers.
  (Github issue :issue:`6836`)

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

* Special float exception values could generate invalid C code.
  (Github issues :issue:`6900`, :issue:`6903`)

* References to the Python ``bool`` type could generate invalid C code.
  (Github issue :issue:`6902`)

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

* Vectorcalls could use needless temp assignments for ``self``.
  (Github issue :issue:`6909`)

* Iterating over temporary memoryviews could crash Cython.
  (Github issue :issue:`7005`)

* Type casts on constants as part of numeric expressions could crash Cython.
  (Github issue :issue:`6779`)

* Long code bodies in ``with`` statements could crash Cython.
  (Github issue :issue:`7122`)

* Indexing ``bytes`` failed to optimise in some cases.
  (Github issue :issue:`6997`)

* Optimised C integer formatting in f-strings failed to apply to typedef types.
  (Github issue :issue:`7170`)

* In auto-pickling, trying to unpickle an object that has no ``__dict__`` from object pickle data
  that includes instance dict state is now an error.
  (Github issue :issue:`7222`)

* The type objects of heap types were not always correctly decrefed on deallocation.
  (Github issue :issue:`7145`)

* Pure mode type aliases like ``p_int`` or ``ulong`` leaked into some C type contexts,
  risking to conflict with user declarations.
  (Github issues :issue:`6922`, :issue:`6339`)

* Boolean (emptyness) tests on builtin containers could fail to handle (unlikely) errors.
  (Github issue :issue:`7090`)

* The return type of ``bytes.join()`` was sometimes inferred as plain ``object``.
  (Github issue :issue:`6987`)

* Type inference could fail to understand ``prange()`` arguments.
  (Github issue :issue:`6974`)

* ``embedsignatures`` failed if ``lambda`` was used in function default arguments.
  (Github issue :issue:`6880`)

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

* ``PyType_FromModuleAndSpec`` was incorrectly used in Limited API code before Py3.10.
  (Github issue :issue:`7181`)

* Conversion code for memoryview dtypes from and to Python objects generated C warnings about
  incorrect ``const`` / non-``const``  casting code.
  (Github issue :issue:`7219`)

* ``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 :issue:`7183`)

* Cython's tools and frontend scripts now use ``python3``  instead of just ``python``
  in their shebang line.
  Patch by Matti Picus.  (Github issue :issue:`7053`)

* The ``setup.py`` script in the ``Demos/`` subdirectory failed to build.
  (Github issue :issue:`7228`)

* Includes all fixes as of Cython 3.1.5.

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

* Usages of `Py_TPFLAGS_HAVE_FINALIZE` were removed.  The constant remains available as cimport from
  ``cpython.object`` for legacy reasons.
  (Github issue :issue:`6423`)

3.2.0b1 (2025-10-22)

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

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

* Builtin exception types are now inferred.
  (Github issue :issue:`6908`)

* The list of known, inferred and optimised Python builtins was updated.
  `range` is now considered a type. `ascii`, `bin`, `format`, `hex`, `oct` were added as functions.
  (Github issue :issue:`6931`)

* The f-string syntax was extended according to PEP-701.
  (Github issue :issue:`5452`)

* t-strings are implemented according to PEP-750.  The implementation backports the template classes
  but prefers existing backports if installed separately.
  (Github issue :issue:`6811`)

* Unknown return type annotations with `->` are no longer rejected but produce warnings.
  This allows better integration with Python type hints that are not always usable for Cython.
  ``-> None``  is also allowed now.
  Patch by jpe.  (Github issue :issue:`6946`)

* The runtime Python dispatch for fused functions is substantially faster.
  (Github issues :issue:`1385`, :issue:`6996`)

* Freelists (via cdef class decorator and for internally used types such as ``async``)
  are now also used in the Limited API and with extension type specs enabled.
  (Github issue :issue:`7151`)

* Module imports now quickly check for an already imported module to speed up reimports.
  Patch by Lysandros Nikolaou.  (Github issue :issue:`7035`)

* Type checks on PEP-604 union types (`int | None`) are optimised into separate checks.
  (Github issue :issue:`6935`)

* Assignments to the PEP-604 union type `float | None` allow any suitable Python number as input
  and convert it to a Python `float` automatically.
  (Github issue :issue:`5750`)

* Item type inference was improved for looping over literals.
  (Github issue :issue:`6912`)

* Looping over literal sequences and strings now uses efficient C array looping if possible.
  (Github issue :issue:`6926`)

* Releasing the GIL from an unknown lock state is more efficient.
  (Github issue :issue:`6847`)

* ``cython.critical_section(PyMutex)`` now works, as with Python objects.
  (Github issue :issue:`6847`)

* ``bool(c_int/float/ptr)`` avoid passing through Python objects.
  (Github issue :issue:`7015`)

* Variables assigned inside of ``prange`` loops can now be initialised outside of the loop.
  (Github issue :issue:`7178`)

* Unused exceptions in ``except`` clauses are detected in some more cases to avoid their normalisation.
  (Github issue :issue:`7021`)

* Mixed operations on C integers with Python ints use less code and are more streamlined for Py3.12+.
  (Github issue :issue:`7244`)

* Some object constants are now marked as ``immortal`` to speed up their reference counting
  in recent CPython versions.  This can be configured with the ``CYTHON_IMMORTAL_CONSTANTS`` C macro.
  (Github issue :issue:`7118`)

* Further improvements were made to reduce the size of the resulting extension modules.
  (Github issue :issue:`6983`, :issue:`7199`, :issue:`7220`, :issue:`7238`)

* Several improvements were made in freethreaded Python code.
  (Github issues :issue:`6936`, :issue:`6939`, :issue:`6949`, :issue:`6984`,
  :issue:`7011`, :issue:`7066`, :issue:`7114`, :issue:`7200`)

* Several improvements were made for the Limited API.
  (Github issues :issue:`6959`, :issue:`6991`)

* Several improvements were made for the GraalPython support.
  Patch by Michael Šimáček.  (Github issue :issue:`7074`)

* Some GIL-safe C-API wrappers were added to the libc/libcpp declarations.
  (Github issue :issue:`6829`, :issue:`6993`)

* String and number constants use less storage space in the module.
  (Github issues :issue:`6971`, :issue:`6978`, :issue:`6986`)

* The managed dict/weakref support in CPython 3.12+ is used for internal types
  to benefit from future CPython optimisations here.
  (Github issue :issue:`6891`)

* Using ``NaN`` as exception return value is supported.
  (Github issues :issue:`6900`, :issue:`6903`)

* Declarations for C++ condition variables were added.
  (Github issue :issue:`6836`)

* The annotated source HTML page shows alternating +/− markers to open/close lines.
  Patch by Kamil Monicz.  (Github issue :issue:`7099`)

* ``cython --embed`` gained a new option ``--embed-modules=…`` to list further extension modules
  that will be statically linked into the generated extension module, to get them initialised
  on application start.
  (Github issue :issue:`2849`)

* The ``setup.py`` script of Cython now allows passing the desired Limited API version
  like ``--cython-limited-api=3.11``.
  (Github issue :issue:`7228`)

* Unicode 16.0.0 is used to parse identifiers.
  (Github issue :issue:`6836`)

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

* Special float exception values could generate invalid C code.
  (Github issues :issue:`6900`, :issue:`6903`)

* References to the Python ``bool`` type could generate invalid C code.
  (Github issue :issue:`6902`)

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

* Vectorcalls could use needless temp assignments for ``self``.
  (Github issue :issue:`6909`)

* Iterating over temporary memoryviews could crash Cython.
  (Github issue :issue:`7005`)

* Type casts on constants as part of numeric expressions could crash Cython.
  (Github issue :issue:`6779`)

* Long code bodies in ``with`` statements could crash Cython.
  (Github issue :issue:`7122`)

* Indexing ``bytes`` failed to optimise in some cases.
  (Github issue :issue:`6997`)

* Optimised C integer formatting in f-strings failed to apply to typedef types.
  (Github issue :issue:`7170`)

* In auto-pickling, trying to unpickle an object that has no ``__dict__`` from object pickle data
  that includes instance dict state is now an error.
  (Github issue :issue:`7222`)

* The type objects of heap types were not always correctly decrefed on deallocation.
  (Github issue :issue:`7145`)

* Pure mode type aliases like ``p_int`` or ``ulong`` leaked into some C type contexts,
  risking to conflict with user declarations.
  (Github issues :issue:`6922`, :issue:`6339`)

* Boolean (emptyness) tests on builtin containers could fail to handle (unlikely) errors.
  (Github issue :issue:`7090`)

* The return type of ``bytes.join()`` was sometimes inferred as plain ``object``.
  (Github issue :issue:`6987`)

* Type inference could fail to understand ``prange()`` arguments.
  (Github issue :issue:`6974`)

* ``embedsignatures`` failed if ``lambda`` was used in function default arguments.
  (Github issue :issue:`6880`)

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

* ``PyType_FromModuleAndSpec`` was incorrectly used in Limited API code before Py3.10.
  (Github issue :issue:`7181`)

* Conversion code for memoryview dtypes from and to Python objects generated C warnings about
  incorrect ``const`` / non-``const``  casting code.
  (Github issue :issue:`7219`)

* ``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 :issue:`7183`)

* Cython's tools and frontend scripts now use ``python3``  instead of just ``python``
  in their shebang line.
  Patch by Matti Picus.  (Github issue :issue:`7053`)

* The ``setup.py`` script in the ``Demos/`` subdirectory failed to build.
  (Github issue :issue:`7228`)

* Includes all fixes as of Cython 3.1.5.

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

* Usages of `Py_TPFLAGS_HAVE_FINALIZE` were removed.  The constant remains available as cimport from
  ``cpython.object`` for legacy reasons.
  (Github issue :issue:`6423`)

3.2.0b1 (2025-10-22)

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

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

* Builtin exception types are now inferred.
  (Github issue :issue:`6908`)

* The list of known, inferred and optimised Python builtins was updated.
  `range` is now considered a type. `ascii`, `bin`, `format`, `hex`, `oct` were added as functions.
  (Github issue :issue:`6931`)

* The f-string syntax was extended according to PEP-701.
  (Github issue :issue:`5452`)

* t-strings are implemented according to PEP-750.  The implementation backports the template classes
  but prefers existing backports if installed separately.
  (Github issue :issue:`6811`)

* Unknown return type annotations with `->` are no longer rejected but produce warnings.
  This allows better integration with Python type hints that are not always usable for Cython.
  ``-> None``  is also allowed now.
  Patch by jpe.  (Github issue :issue:`6946`)

* The runtime Python dispatch for fused functions is substantially faster.
  (Github issues :issue:`1385`, :issue:`6996`)

* Freelists (via cdef class decorator and for internally used types such as ``async``)
  are now also used in the Limited API and with extension type specs enabled.
  (Github issue :issue:`7151`)

* Module imports now quickly check for an already imported module to speed up reimports.
  Patch by Lysandros Nikolaou.  (Github issue :issue:`7035`)

* Type checks on PEP-604 union types (`int | None`) are optimised into separate checks.
  (Github issue :issue:`6935`)

* Assignments to the PEP-604 union type `float | None` allow any suitable Python number as input
  and convert it to a Python `float` automatically.
  (Github issue :issue:`5750`)

* Item type inference was improved for looping over literals.
  (Github issue :issue:`6912`)

* Looping over literal sequences and strings now uses efficient C array looping if possible.
  (Github issue :issue:`6926`)

* Releasing the GIL from an unknown lock state is more efficient.
  (Github issue :issue:`6847`)

* ``cython.critical_section(PyMutex)`` now works, as with Python objects.
  (Github issue :issue:`6847`)

* ``bool(c_int/float/ptr)`` avoid passing through Python objects.
  (Github issue :issue:`7015`)

* Variables assigned inside of ``prange`` loops can now be initialised outside of the loop.
  (Github issue :issue:`7178`)

* Unused exceptions in ``except`` clauses are detected in some more cases to avoid their normalisation.
  (Github issue :issue:`7021`)

* Mixed operations on C integers with Python ints use less code and are more streamlined for Py3.12+.
  (Github issue :issue:`7244`)

* Some object constants are now marked as ``immortal`` to speed up their reference counting
  in recent CPython versions.  This can be configured with the ``CYTHON_IMMORTAL_CONSTANTS`` C macro.
  (Github issue :issue:`7118`)

* Further improvements were made to reduce the size of the resulting extension modules.
  (Github issue :issue:`6983`, :issue:`7199`, :issue:`7220`, :issue:`7238`)

* Several improvements were made in freethreaded Python code.
  (Github issues :issue:`6936`, :issue:`6939`, :issue:`6949`, :issue:`6984`,
  :issue:`7011`, :issue:`7066`, :issue:`7114`, :issue:`7200`)

* Several improvements were made for the Limited API.
  (Github issues :issue:`6959`, :issue:`6991`)

* Several improvements were made for the GraalPython support.
  Patch by Michael Šimáček.  (Github issue :issue:`7074`)

* Some GIL-safe C-API wrappers were added to the libc/libcpp declarations.
  (Github issue :issue:`6829`, :issue:`6993`)

* String and number constants use less storage space in the module.
  (Github issues :issue:`6971`, :issue:`6978`, :issue:`6986`)

* The managed dict/weakref support in CPython 3.12+ is used for internal types
  to benefit from future CPython optimisations here.
  (Github issue :issue:`6891`)

* Using ``NaN`` as exception return value is supported.
  (Github issues :issue:`6900`, :issue:`6903`)

* Declarations for C++ condition variables were added.
  (Github issue :issue:`6836`)

* The annotated source HTML page shows alternating +/− markers to open/close lines.
  Patch by Kamil Monicz.  (Github issue :issue:`7099`)

* ``cython --embed`` gained a new option ``--embed-modules=…`` to list further extension modules
  that will be statically linked into the generated extension module, to get them initialised
  on application start.
  (Github issue :issue:`2849`)

* The ``setup.py`` script of Cython now allows passing the desired Limited API version
  like ``--cython-limited-api=3.11``.
  (Github issue :issue:`7228`)

* Unicode 16.0.0 is used to parse identifiers.
  (Github issue :issue:`6836`)

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

* Special float exception values could generate invalid C code.
  (Github issues :issue:`6900`, :issue:`6903`)

* References to the Python ``bool`` type could generate invalid C code.
  (Github issue :issue:`6902`)

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

* Vectorcalls could use needless temp assignments for ``self``.
  (Github issue :issue:`6909`)

* Iterating over temporary memoryviews could crash Cython.
  (Github issue :issue:`7005`)

* Type casts on constants as part of numeric expressions could crash Cython.
  (Github issue :issue:`6779`)

* Long code bodies in ``with`` statements could crash Cython.
  (Github issue :issue:`7122`)

* Indexing ``bytes`` failed to optimise in some cases.
  (Github issue :issue:`6997`)

* Optimised C integer formatting in f-strings failed to apply to typedef types.
  (Github issue :issue:`7170`)

* In auto-pickling, trying to unpickle an object that has no ``__dict__`` from object pickle data
  that includes instance dict state is now an error.
  (Github issue :issue:`7222`)

* The type objects of heap types were not always correctly decrefed on deallocation.
  (Github issue :issue:`7145`)

* Pure mode type aliases like ``p_int`` or ``ulong`` leaked into some C type contexts,
  risking to conflict with user declarations.
  (Github issues :issue:`6922`, :issue:`6339`)

* Boolean (emptyness) tests on builtin containers could fail to handle (unlikely) errors.
  (Github issue :issue:`7090`)

* The return type of ``bytes.join()`` was sometimes inferred as plain ``object``.
  (Github issue :issue:`6987`)

* Type inference could fail to understand ``prange()`` arguments.
  (Github issue :issue:`6974`)

* ``embedsignatures`` failed if ``lambda`` was used in function default arguments.
  (Github issue :issue:`6880`)

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

* ``PyType_FromModuleAndSpec`` was incorrectly used in Limited API code before Py3.10.
  (Github issue :issue:`7181`)

* Conversion code for memoryview dtypes from and to Python objects generated C warnings about
  incorrect ``const`` / non-``const``  casting code.
  (Github issue :issue:`7219`)

* ``cythonize`` (program and function) now uses :class:`concurrent.futures.ProcessPoolExecutor`
  instead of :class:`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 :issue:`7183`)

* Cython's tools and frontend scripts now use ``python3``  instead of just ``python``
  in their shebang line.
  Patch by Matti Picus.  (Github issue :issue:`7053`)

* The ``setup.py`` script in the ``Demos/`` subdirectory failed to build.
  (Github issue :issue:`7228`)

* Includes all fixes as of Cython 3.1.5.

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

* Usages of `Py_TPFLAGS_HAVE_FINALIZE` were removed.  The constant remains available as cimport from
  ``cpython.object`` for legacy reasons.
  (Github issue :issue:`6423`)

3.1.5 (2025-01-19)

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

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 :issue:`7157`)

* Optimised unpacking of Python integers in expressions uses a slightly safer scheme.
  (Github issue :issue:`7134`)

* Empty return statements were not always reported when tracing.
  (Github issue :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 :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 :issue:`6836`)

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

* The monitoring code could crash on tracing.
  (Github issue :issue:`7050`)

* Initialising the monitoring code could fail with a CPython exception.
  See nedbat/coveragepy#1790 (comment)

* Optimised integer shifting triggered undefined behaviour in C.
  (Github issue :issue:`7089`)

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

* A reference to metaclasses could be leaked on instantiation.
  (Github issue :issue:`7130`)

* (Unlikely) error handling during empty builtin container tests was ineffective.
  (Github issue :issue:`7190`)

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

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

* The ``@cython.ufunc``  decorator was missing in type checker stubs.
  Patch by jayClean.  (Github issue :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 :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`)