cpython/Doc/whatsnew/3.14.rst

****************************
  What's New In Python 3.14
****************************

:Editor: TBD

.. Rules for maintenance:

   * Anyone can add text to this document.  Do not spend very much time
   on the wording of your changes, because your text will probably
   get rewritten to some degree.

   * The maintainer will go through Misc/NEWS periodically and add
   changes; it's therefore more important to add your changes to
   Misc/NEWS than to this file.

   * This is not a complete list of every single change; completeness
   is the purpose of Misc/NEWS.  Some changes I consider too small
   or esoteric to include.  If such a change is added to the text,
   I'll just remove it.  (This is another reason you shouldn't spend
   too much time on writing your addition.)

   * If you want to draw your new text to the attention of the
   maintainer, add 'XXX' to the beginning of the paragraph or
   section.

   * It's OK to just add a fragmentary note about a change.  For
   example: "XXX Describe the transmogrify() function added to the
   socket module."  The maintainer will research the change and
   write the necessary text.

   * You can comment out your additions if you like, but it's not
   necessary (especially when a final release is some months away).

   * Credit the author of a patch or bugfix.   Just the name is
   sufficient; the e-mail address isn't necessary.

   * It's helpful to add the issue number as a comment:

   XXX Describe the transmogrify() function added to the socket
   module.
   (Contributed by P.Y. Developer in :gh:`12345`.)

   This saves the maintainer the effort of going through the VCS log
   when researching a change.

This article explains the new features in Python 3.14, compared to 3.13.

For full details, see the :ref:`changelog <changelog>`.

.. note::

   Prerelease users should be aware that this document is currently in draft
   form. It will be updated substantially as Python 3.14 moves towards release,
   so it's worth checking back even after reading earlier versions.


Summary -- Release highlights
=============================

.. This section singles out the most important changes in Python 3.14.
   Brevity is key.


.. PEP-sized items next.



New Features
============

.. _whatsnew-314-pep649:

PEP 649: Deferred Evaluation of Annotations
-------------------------------------------

The :term:`annotations <annotation>` on functions, classes, and modules are no
longer evaluated eagerly. Instead, annotations are stored in special-purpose
:term:`annotate functions <annotate function>` and evaluated only when
necessary. This is specified in :pep:`649` and :pep:`749`.

This change is designed to make annotations in Python more performant and more
usable in most circumstances. The runtime cost for defining annotations is
minimized, but it remains possible to introspect annotations at runtime.
It is usually no longer necessary to enclose annotations in strings if they
contain forward references.

The new :mod:`annotationlib` module provides tools for inspecting deferred
annotations. Annotations may be evaluated in the :attr:`~annotationlib.Format.VALUE`
format (which evaluates annotations to runtime values, similar to the behavior in
earlier Python versions), the :attr:`~annotationlib.Format.FORWARDREF` format
(which replaces undefined names with special markers), and the
:attr:`~annotationlib.Format.SOURCE` format (which returns annotations as strings).

This example shows how these formats behave:

.. doctest::

   >>> from annotationlib import get_annotations, Format
   >>> def func(arg: Undefined):
   ...     pass
   >>> get_annotations(func, format=Format.VALUE)
   Traceback (most recent call last):
     ...
   NameError: name 'Undefined' is not defined
   >>> get_annotations(func, format=Format.FORWARDREF)
   {'arg': ForwardRef('Undefined')}
   >>> get_annotations(func, format=Format.SOURCE)
   {'arg': 'Undefined'}

Implications for annotated code
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you define annotations in your code (for example, for use with a static type
checker), then this change probably does not affect you: you can keep
writing annotations the same way you did with previous versions of Python.

You will likely be able to remove quoted strings in annotations, which are frequently
used for forward references. Similarly, if you use ``from __future__ import annotations``
to avoid having to write strings in annotations, you may well be able to
remove that import. However, if you rely on third-party libraries that read annotations,
those libraries may need changes to support unquoted annotations before they
work as expected.

Implications for readers of ``__annotations__``
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If your code reads the ``__annotations__`` attribute on objects, you may want
to make changes in order to support code that relies on deferred evaluation of
annotations. For example, you may want to use :func:`annotationlib.get_annotations`
with the :attr:`~annotationlib.Format.FORWARDREF` format, as the :mod:`dataclasses`
module now does.

Related changes
^^^^^^^^^^^^^^^

The changes in Python 3.14 are designed to rework how ``__annotations__``
works at runtime while minimizing breakage to code that contains
annotations in source code and to code that reads ``__annotations__``. However,
if you rely on undocumented details of the annotation behavior or on private
functions in the standard library, there are many ways in which your code may
not work in Python 3.14. To safeguard your code against future changes,
use only the documented functionality of the :mod:`annotationlib` module.

``from __future__ import annotations``
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In Python 3.7, :pep:`563` introduced the ``from __future__ import annotations``
directive, which turns all annotations into strings. This directive is now
considered deprecated and it is expected to be removed in a future version of Python.
However, this removal will not happen until after Python 3.13, the last version of
Python without deferred evaluation of annotations, reaches its end of life.
In Python 3.14, the behavior of code using ``from __future__ import annotations``
is unchanged.


Improved Error Messages
-----------------------

* When unpacking assignment fails due to incorrect number of variables, the
  error message prints the received number of values in more cases than before.
  (Contributed by Tushar Sadhwani in :gh:`122239`.)

  .. code-block:: pycon

     >>> x, y, z = 1, 2, 3, 4
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
         x, y, z = 1, 2, 3, 4
         ^^^^^^^
     ValueError: too many values to unpack (expected 3, got 4)


Other Language Changes
======================

* Incorrect usage of :keyword:`await` and asynchronous comprehensions
  is now detected even if the code is optimized away by the :option:`-O`
  command line option. For example, ``python -O -c 'assert await 1'``
  now produces a :exc:`SyntaxError`. (Contributed by Jelle Zijlstra in :gh:`121637`.)

* Writes to ``__debug__`` are now detected even if the code is optimized
  away by the :option:`-O` command line option. For example,
  ``python -O -c 'assert (__debug__ := 1)'`` now produces a
  :exc:`SyntaxError`. (Contributed by Irit Katriel in :gh:`122245`.)

* Added class methods :meth:`float.from_number` and :meth:`complex.from_number`
  to convert a number to :class:`float` or :class:`complex` type correspondingly.
  They raise an error if the argument is a string.
  (Contributed by Serhiy Storchaka in :gh:`84978`.)


New Modules
===========

* :mod:`annotationlib`: For introspecting :term:`annotations <annotation>`.
  See :pep:`749` for more details.
  (Contributed by Jelle Zijlstra in :gh:`119180`.)


Improved Modules
================


ast
---

* Added :func:`ast.compare` for comparing two ASTs.
  (Contributed by Batuhan Taskaya and Jeremy Hylton in :issue:`15987`.)

* Add support for :func:`copy.replace` for AST nodes.
  (Contributed by Bénédikt Tran in :gh:`121141`.)

* Docstrings are now removed from an optimized AST in optimization level 2.
  (Contributed by Irit Katriel in :gh:`123958`.)


ctypes
------

* The layout of :ref:`bit fields <ctypes-bit-fields-in-structures-unions>`
  in :class:`~ctypes.Structure` and :class:`~ctypes.Union`
  now matches platform defaults (GCC/Clang or MVSC) more closely.
  In particular, fields no longer overlap.
  (Contributed by Matthias Görgens in :gh:`97702`.)

* The :attr:`.Structure._layout_` class attribute can now be set
  to help match a non-default ABI.
  (Contributed by Petr Viktorin in :gh:`97702`.)


dis
---

* Added support for rendering full source location information of
  :class:`instructions <dis.Instruction>`, rather than only the line number.
  This feature is added to the following interfaces via the ``show_positions``
  keyword argument:

  - :class:`dis.Bytecode`,
  - :func:`dis.dis`, :func:`dis.distb`, and
  - :func:`dis.disassemble`.

  This feature is also exposed via :option:`dis --show-positions`.

  (Contributed by Bénédikt Tran in :gh:`123165`.)


fractions
---------

Added support for converting any objects that have the
:meth:`!as_integer_ratio` method to a :class:`~fractions.Fraction`.
(Contributed by Serhiy Storchaka in :gh:`82017`.)


http
----

Directory lists and error pages generated by the :mod:`http.server`
module allow the browser to apply its default dark mode.
(Contributed by Yorik Hansen in :gh:`123430`.)


json
----

Add notes for JSON serialization errors that allow to identify the source
of the error.
(Contributed by Serhiy Storchaka in :gh:`122163`.)

Enable :mod:`json` module to work as a script using the :option:`-m` switch: ``python -m json``.
See the :ref:`JSON command-line interface <json-commandline>` documentation.
(Contributed by Trey Hunner in :gh:`122873`.)


operator
--------

* Two new functions ``operator.is_none`` and ``operator.is_not_none``
  have been added, such that ``operator.is_none(obj)`` is equivalent
  to ``obj is None`` and ``operator.is_not_none(obj)`` is equivalent
  to ``obj is not None``.
  (Contributed by Raymond Hettinger and Nico Mexis in :gh:`115808`.)


os
--

* Added the :data:`os.environ.refresh() <os.environ>` method to update
  :data:`os.environ` with changes to the environment made by :func:`os.putenv`,
  by :func:`os.unsetenv`, or made outside Python in the same process.
  (Contributed by Victor Stinner in :gh:`120057`.)


pathlib
-------

* Add methods to :class:`pathlib.Path` to recursively copy or move files and
  directories:

  * :meth:`~pathlib.Path.copy` copies a file or directory tree to a destination.
  * :meth:`~pathlib.Path.copy_into` copies *into* a destination directory.
  * :meth:`~pathlib.Path.move` moves a file or directory tree to a destination.
  * :meth:`~pathlib.Path.move_into` moves *into* a destination directory.

  (Contributed by Barney Gale in :gh:`73991`.)


pdb
---

* Hard-coded breakpoints (:func:`breakpoint` and :func:`pdb.set_trace`) now
  reuse the most recent :class:`~pdb.Pdb` instance that calls
  :meth:`~pdb.Pdb.set_trace`, instead of creating a new one each time.
  As a result, all the instance specific data like :pdbcmd:`display` and
  :pdbcmd:`commands` are preserved across hard-coded breakpoints.
  (Contributed by Tian Gao in :gh:`121450`.)


pickle
------

* Set the default protocol version on the :mod:`pickle` module to 5.
  For more details, please see :ref:`pickle protocols <pickle-protocols>`.

* Add notes for pickle serialization errors that allow to identify the source
  of the error.
  (Contributed by Serhiy Storchaka in :gh:`122213`.)

symtable
--------

* Expose the following :class:`symtable.Symbol` methods:

  * :meth:`~symtable.Symbol.is_free_class`
  * :meth:`~symtable.Symbol.is_comp_iter`
  * :meth:`~symtable.Symbol.is_comp_cell`

  (Contributed by Bénédikt Tran in :gh:`120029`.)

unicodedata
-----------

* The Unicode database has been updated to Unicode 16.0.0.

.. Add improved modules above alphabetically, not here at the end.

Optimizations
=============

asyncio
-------

* :mod:`asyncio` now uses double linked list implementation for native tasks
  which speeds up execution by 10% on standard pyperformance benchmarks and
  reduces memory usage.
  (Contributed by Kumar Aditya in :gh:`107803`.)

Deprecated
==========

* :mod:`builtins`:
  Passing a complex number as the *real* or *imag* argument in the
  :func:`complex` constructor is now deprecated; it should only be passed
  as a single positional argument.
  (Contributed by Serhiy Storchaka in :gh:`109218`.)

* :mod:`os`:
  :term:`Soft deprecate <soft deprecated>` :func:`os.popen` and
  :func:`os.spawn* <os.spawnl>` functions. They should no longer be used to
  write new code.  The :mod:`subprocess` module is recommended instead.
  (Contributed by Victor Stinner in :gh:`120743`.)

* :mod:`symtable`:
  Deprecate :meth:`symtable.Class.get_methods` due to the lack of interest.
  (Contributed by Bénédikt Tran in :gh:`119698`.)

.. Add deprecations above alphabetically, not here at the end.

.. include:: ../deprecations/pending-removal-in-3.15.rst

.. include:: ../deprecations/pending-removal-in-3.16.rst

.. include:: ../deprecations/pending-removal-in-future.rst

Removed
=======

argparse
--------

* Remove the *type*, *choices*, and *metavar* parameters
  of :class:`!argparse.BooleanOptionalAction`.
  They were deprecated since 3.12.

ast
---

* Remove the following classes. They were all deprecated since Python 3.8,
  and have emitted deprecation warnings since Python 3.12:

  * :class:`!ast.Num`
  * :class:`!ast.Str`
  * :class:`!ast.Bytes`
  * :class:`!ast.NameConstant`
  * :class:`!ast.Ellipsis`

  Use :class:`ast.Constant` instead. As a consequence of these removals,
  user-defined ``visit_Num``, ``visit_Str``, ``visit_Bytes``,
  ``visit_NameConstant`` and ``visit_Ellipsis`` methods on custom
  :class:`ast.NodeVisitor` subclasses will no longer be called when the
  ``NodeVisitor`` subclass is visiting an AST. Define a ``visit_Constant``
  method instead.

  Also, remove the following deprecated properties on :class:`ast.Constant`,
  which were present for compatibility with the now-removed AST classes:

  * :attr:`!ast.Constant.n`
  * :attr:`!ast.Constant.s`

  Use :attr:`!ast.Constant.value` instead.

  (Contributed by Alex Waygood in :gh:`119562`.)

asyncio
-------

* Remove the following classes and functions. They were all deprecated and
  emitted deprecation warnings since Python 3.12:

  * :class:`!asyncio.AbstractChildWatcher`
  * :class:`!asyncio.SafeChildWatcher`
  * :class:`!asyncio.MultiLoopChildWatcher`
  * :class:`!asyncio.FastChildWatcher`
  * :class:`!asyncio.ThreadedChildWatcher`
  * :class:`!asyncio.PidfdChildWatcher`
  * :meth:`!asyncio.AbstractEventLoopPolicy.get_child_watcher`
  * :meth:`!asyncio.AbstractEventLoopPolicy.set_child_watcher`
  * :func:`!asyncio.get_child_watcher`
  * :func:`!asyncio.set_child_watcher`

  (Contributed by Kumar Aditya in :gh:`120804`.)

collections.abc
---------------

* Remove :class:`!collections.abc.ByteString`. It had previously raised a
  :exc:`DeprecationWarning` since Python 3.12.

email
-----

* Remove the *isdst* parameter from :func:`email.utils.localtime`.
  (Contributed by Hugo van Kemenade in :gh:`118798`.)

importlib
---------

* Remove deprecated :mod:`importlib.abc` classes:

  * :class:`!importlib.abc.ResourceReader`
  * :class:`!importlib.abc.Traversable`
  * :class:`!importlib.abc.TraversableResources`

  Use :mod:`importlib.resources.abc` classes instead:

  * :class:`importlib.resources.abc.Traversable`
  * :class:`importlib.resources.abc.TraversableResources`

  (Contributed by Jason R. Coombs and Hugo van Kemenade in :gh:`93963`.)

itertools
---------

* Remove :mod:`itertools` support for copy, deepcopy, and pickle operations.
  These had previously raised a :exc:`DeprecationWarning` since Python 3.12.
  (Contributed by Raymond Hettinger in :gh:`101588`.)

pathlib
-------

* Remove support for passing additional keyword arguments to
  :class:`pathlib.Path`. In previous versions, any such arguments are ignored.
* Remove support for passing additional positional arguments to
  :meth:`pathlib.PurePath.relative_to` and
  :meth:`~pathlib.PurePath.is_relative_to`. In previous versions, any such
  arguments are joined onto *other*.

pty
---

* Remove deprecated :func:`!pty.master_open` and :func:`!pty.slave_open`.
  They had previously raised a :exc:`DeprecationWarning` since Python 3.12.
  Use :func:`pty.openpty` instead.
  (Contributed by Nikita Sobolev in :gh:`118824`.)

sqlite3
-------

* Remove :data:`!version` and :data:`!version_info` from :mod:`sqlite3`.
  (Contributed by Hugo van Kemenade in :gh:`118924`.)

* Disallow using a sequence of parameters with named placeholders.
  This had previously raised a :exc:`DeprecationWarning` since Python 3.12;
  it will now raise a :exc:`sqlite3.ProgrammingError`.
  (Contributed by Erlend E. Aasland in :gh:`118928` and :gh:`101693`.)

typing
------

* Remove :class:`!typing.ByteString`. It had previously raised a
  :exc:`DeprecationWarning` since Python 3.12.

urllib
------

* Remove deprecated :class:`!Quoter` class from :mod:`urllib.parse`.
  It had previously raised a :exc:`DeprecationWarning` since Python 3.11.
  (Contributed by Nikita Sobolev in :gh:`118827`.)

Others
------

* Using :data:`NotImplemented` in a boolean context will now raise a :exc:`TypeError`.
  It had previously raised a :exc:`DeprecationWarning` since Python 3.9. (Contributed
  by Jelle Zijlstra in :gh:`118767`.)

* The :func:`int` built-in no longer delegates to
  :meth:`~object.__trunc__`. Classes that want to support conversion to
  integer must implement either :meth:`~object.__int__` or
  :meth:`~object.__index__`. (Contributed by Mark Dickinson in :gh:`119743`.)


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`.)

Build Changes
=============


C API Changes
=============

New Features
------------

* Add :c:func:`PyLong_GetSign` function to get the sign of :class:`int` objects.
  (Contributed by Sergey B Kirpichev in :gh:`116560`.)

* Add a new :c:type:`PyUnicodeWriter` API to create a Python :class:`str`
  object:

  * :c:func:`PyUnicodeWriter_Create`.
  * :c:func:`PyUnicodeWriter_Discard`.
  * :c:func:`PyUnicodeWriter_Finish`.
  * :c:func:`PyUnicodeWriter_WriteChar`.
  * :c:func:`PyUnicodeWriter_WriteUTF8`.
  * :c:func:`PyUnicodeWriter_WriteUCS4`.
  * :c:func:`PyUnicodeWriter_WriteWideChar`.
  * :c:func:`PyUnicodeWriter_WriteStr`.
  * :c:func:`PyUnicodeWriter_WriteRepr`.
  * :c:func:`PyUnicodeWriter_WriteSubstring`.
  * :c:func:`PyUnicodeWriter_Format`.
  * :c:func:`PyUnicodeWriter_DecodeUTF8Stateful`.

  (Contributed by Victor Stinner in :gh:`119182`.)

* Add :c:func:`PyIter_NextItem` to replace :c:func:`PyIter_Next`,
  which has an ambiguous return value.
  (Contributed by Irit Katriel and Erlend Aasland in :gh:`105201`.)

* :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 exectuion 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.
  (Contribued by Eddie Elizondo in :gh:`113601`.)

* Add new functions to convert C ``<stdint.h>`` numbers from/to Python
  :class:`int`:

  * :c:func:`PyLong_FromInt32`
  * :c:func:`PyLong_FromInt64`
  * :c:func:`PyLong_FromUInt32`
  * :c:func:`PyLong_FromUInt64`
  * :c:func:`PyLong_AsInt32`
  * :c:func:`PyLong_AsInt64`
  * :c:func:`PyLong_AsUInt32`
  * :c:func:`PyLong_AsUInt64`

  (Contributed by Victor Stinner in :gh:`120389`.)

* Add :c:func:`PyBytes_Join(sep, iterable) <PyBytes_Join>` function,
  similar to ``sep.join(iterable)`` in Python.
  (Contributed by Victor Stinner in :gh:`121645`.)

* Add :c:func:`Py_HashBuffer` to compute and return the hash value of a buffer.
  (Contributed by Antoine Pitrou and Victor Stinner in :gh:`122854`.)

* Add functions to get and set the current runtime Python configuration
  (:pep:`741`):

  * :c:func:`PyConfig_Get`
  * :c:func:`PyConfig_GetInt`
  * :c:func:`PyConfig_Set`
  * :c:func:`PyConfig_Names`

  (Contributed by Victor Stinner in :gh:`107954`.)

* Add functions to configure the Python initialization (:pep:`741`):

  * :c:func:`PyInitConfig_Create`
  * :c:func:`PyInitConfig_Free`
  * :c:func:`PyInitConfig_GetError`
  * :c:func:`PyInitConfig_GetExitCode`
  * :c:func:`PyInitConfig_HasOption`
  * :c:func:`PyInitConfig_GetInt`
  * :c:func:`PyInitConfig_GetStr`
  * :c:func:`PyInitConfig_GetStrList`
  * :c:func:`PyInitConfig_FreeStrList`
  * :c:func:`PyInitConfig_SetInt`
  * :c:func:`PyInitConfig_SetStr`
  * :c:func:`PyInitConfig_SetStrList`
  * :c:func:`PyInitConfig_AddModule`
  * :c:func:`Py_InitializeFromInitConfig`

  (Contributed by Victor Stinner in :gh:`107954`.)

* Add :c:func:`PyType_GetBaseByToken` and :c:data:`Py_tp_token` slot for easier
  superclass identification, which attempts to resolve the `type checking issue
  <https://peps.python.org/pep-0630/#type-checking>`__ mentioned in :pep:`630`
  (:gh:`124153`).


Porting to Python 3.14
----------------------

* In the limited C API 3.14 and newer, :c:func:`Py_TYPE` is now implemented as
  an opaque function call to hide implementation details.
  (Contributed by Victor Stinner in :gh:`120600`.)


Deprecated
----------

* Macros :c:macro:`!Py_IS_NAN`, :c:macro:`!Py_IS_INFINITY`
  and :c:macro:`!Py_IS_FINITE` are :term:`soft deprecated`,
  use instead :c:macro:`!isnan`, :c:macro:`!isinf` and
  :c:macro:`!isfinite` available from :file:`math.h`
  since C99.  (Contributed by Sergey B Kirpichev in :gh:`119613`.)

* :func:`!asyncio.iscoroutinefunction` is deprecated
  and will be removed in Python 3.16,
  use :func:`inspect.iscoroutinefunction` instead.
  (Contributed by Jiahao Li and Kumar Aditya in :gh:`122875`.)

.. Add deprecations above alphabetically, not here at the end.

.. include:: ../deprecations/c-api-pending-removal-in-3.15.rst

.. include:: ../deprecations/c-api-pending-removal-in-future.rst

Removed
-------

* Creating :c:data:`immutable types <Py_TPFLAGS_IMMUTABLETYPE>` with mutable
  bases was deprecated since 3.12 and now raises a :exc:`TypeError`.