Porting to Python 3.14

This section lists previously described changes and other bugfixes

that may require changes to your code.

Changes in the Python API

* :class:`functools.partial` is now a method descriptor.

Wrap it in :func:`staticmethod` if you want to preserve the old behavior.

(Contributed by Serhiy Storchaka and Dominykas Grigonis in :gh:`121027`.)

* The :ref:`garbage collector is now incremental <whatsnew314-incremental-gc>`,

which means that the behavior of :func:`gc.collect` changes slightly:

* ``gc.collect(1)``: Performs an increment of garbage collection,

rather than collecting generation 1.

* Other calls to :func:`!gc.collect` are unchanged.

* The :func:`locale.nl_langinfo` function now temporarily sets the ``LC_CTYPE``

locale in some cases.

This temporary change affects other threads.

(Contributed by Serhiy Storchaka in :gh:`69998`.)

* :class:`types.UnionType` is now an alias for :class:`typing.Union`,

causing changes in some behaviors.

See :ref:`above <whatsnew314-typing-union>` for more details.

(Contributed by Jelle Zijlstra in :gh:`105499`.)

* The runtime behavior of annotations has changed in various ways; see

:ref:`above <whatsnew314-pep649>` for details. While most code that interacts

with annotations should continue to work, some undocumented details may behave

differently.

Porting to Python 3.14

* :c:func:`Py_Finalize` now deletes all interned strings. This

is backwards incompatible to any C-Extension that holds onto an interned

string after a call to :c:func:`Py_Finalize` and is then reused after a

call to :c:func:`Py_Initialize`. Any issues arising from this behavior will

normally result in crashes during the execution of the subsequent call to

:c:func:`Py_Initialize` from accessing uninitialized memory. To fix, use

an address sanitizer to identify any use-after-free coming from

an interned string and deallocate it during module shutdown.

(Contributed by Eddie Elizondo in :gh:`113601`.)

* The :ref:`Unicode Exception Objects <unicodeexceptions>` C API

now raises a :exc:`TypeError` if its exception argument is not

a :exc:`UnicodeError` object.

(Contributed by Bénédikt Tran in :gh:`127691`.)

.. _whatsnew314-refcount:

* The interpreter internally avoids some reference count modifications when

loading objects onto the operands stack by :term:`borrowing <borrowed reference>`

references when possible. This can lead to smaller reference count values

compared to previous Python versions. C API extensions that checked

:c:func:`Py_REFCNT` of ``1`` to determine if an function argument is not

referenced by any other code should instead use

:c:func:`PyUnstable_Object_IsUniqueReferencedTemporary` as a safer replacement.

* Private functions promoted to public C APIs:

* ``_PyBytes_Join()``: :c:func:`PyBytes_Join`

* ``_PyLong_IsNegative()``: :c:func:`PyLong_IsNegative`

* ``_PyLong_IsPositive()``: :c:func:`PyLong_IsPositive`

* ``_PyLong_IsZero()``: :c:func:`PyLong_IsZero`

* ``_PyLong_Sign()``: :c:func:`PyLong_GetSign`

* ``_PyUnicodeWriter_Dealloc()``: :c:func:`PyUnicodeWriter_Discard`

* ``_PyUnicodeWriter_Finish()``: :c:func:`PyUnicodeWriter_Finish`

* ``_PyUnicodeWriter_Init()``: use :c:func:`PyUnicodeWriter_Create`

* ``_PyUnicodeWriter_Prepare()``: (no replacement)

* ``_PyUnicodeWriter_PrepareKind()``: (no replacement)

* ``_PyUnicodeWriter_WriteChar()``: :c:func:`PyUnicodeWriter_WriteChar`

* ``_PyUnicodeWriter_WriteStr()``: :c:func:`PyUnicodeWriter_WriteStr`

* ``_PyUnicodeWriter_WriteSubstring()``: :c:func:`PyUnicodeWriter_WriteSubstring`

* ``_PyUnicode_EQ()``: :c:func:`PyUnicode_Equal`

* ``_PyUnicode_Equal()``: :c:func:`PyUnicode_Equal`

* ``_Py_GetConfig()``: :c:func:`PyConfig_Get` and :c:func:`PyConfig_GetInt`

* ``_Py_HashBytes()``: :c:func:`Py_HashBuffer`

* ``_Py_fopen_obj()``: :c:func:`Py_fopen`

* ``PyMutex_IsLocked()`` : :c:func:`PyMutex_IsLocked`

The `pythoncapi-compat project`_ can be used to get most of these new

functions on Python 3.13 and older.

.. _pythoncapi-compat project: https://github.com/python/pythoncapi-compat/