
****************************
  What's new in Python 3.14
****************************

:Editors: Adam Turner and Hugo van Kemenade

.. 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.
Python 3.14 was released on 7 October 2025.
For full details, see the :ref:`changelog <changelog>`.

.. seealso::

   :pep:`745` -- Python 3.14 release schedule


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

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

Python 3.14 is the latest stable release of the Python programming
language, with a mix of changes to the language, the implementation,
and the standard library.
The biggest changes include :ref:`template string literals
<whatsnew314-template-string-literals>`,
:ref:`deferred evaluation of annotations <whatsnew314-deferred-annotations>`,
and support for :ref:`subinterpreters <whatsnew314-multiple-interpreters>` in
the standard library.

The library changes include significantly improved capabilities for
:ref:`introspection in asyncio <whatsnew314-asyncio-introspection>`,
:ref:`support for Zstandard <whatsnew314-zstandard>` via a new
:mod:`compression.zstd` module, syntax highlighting in the REPL,
as well as the usual deprecations and removals,
and improvements in user-friendliness and correctness.

This article doesn't attempt to provide a complete specification
of all new features, but instead gives a convenient overview.
For full details refer to the documentation,
such as the :ref:`Library Reference <library-index>`
and :ref:`Language Reference <reference-index>`.
To understand the complete implementation and design rationale for a change,
refer to the PEP for a particular new feature;
but note that PEPs usually are not kept up-to-date
once a feature has been fully implemented.
See `Porting to Python 3.14`_ for guidance on upgrading from
earlier versions of Python.

--------------

.. PEP-sized items next.

Interpreter improvements:

* :pep:`649` and :pep:`749`: :ref:`Deferred evaluation of annotations
  <whatsnew314-deferred-annotations>`
* :pep:`734`: :ref:`Multiple interpreters in the standard library
  <whatsnew314-multiple-interpreters>`
* :pep:`750`: :ref:`Template strings <whatsnew314-template-string-literals>`
* :pep:`758`: :ref:`Allow except and except* expressions without brackets
  <whatsnew314-bracketless-except>`
* :pep:`765`: :ref:`Control flow in finally blocks
  <whatsnew314-finally-syntaxwarning>`
* :pep:`768`: :ref:`Safe external debugger interface for CPython
  <whatsnew314-remote-debugging>`
* :ref:`A new type of interpreter <whatsnew314-tail-call-interpreter>`
* :ref:`Free-threaded mode improvements <whatsnew314-free-threaded-cpython>`
* :ref:`Improved error messages <whatsnew314-improved-error-messages>`
* :ref:`Incremental garbage collection <whatsnew314-incremental-gc>`

Significant improvements in the standard library:

* :pep:`784`: :ref:`Zstandard support in the standard library
  <whatsnew314-zstandard>`
* :ref:`whatsnew314-asyncio-introspection`
* :ref:`whatsnew314-concurrent-warnings-control`
* :ref:`Syntax highlighting in the default interactive shell
  <whatsnew314-pyrepl-highlighting>`, and color output in several
  standard library CLIs

C API improvements:

* :pep:`741`: :ref:`Python configuration C API <whatsnew314-capi-config>`

Platform support:

* :pep:`776`: Emscripten is now an :ref:`officially supported platform
  <whatsnew314-build-changes>`, at :pep:`tier 3 <11#tier-3>`.

Release changes:

* :pep:`779`: :ref:`Free-threaded Python is officially supported
  <whatsnew314-free-threaded-now-supported>`
* :pep:`761`: :ref:`PGP signatures have been discontinued for official releases
  <whatsnew314-no-more-pgp>`
* :ref:`Windows and macOS binary releases now support the experimental
  just-in-time compiler <whatsnew314-jit-compiler>`
* :ref:`Binary releases for Android are now provided <whatsnew314-build-changes>`


New features
============

.. _whatsnew314-deferred-annotations:

:pep:`649` & :pep:`749`: 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 (except if ``from __future__ import annotations`` is used).

This change is designed to improve performance and usability of annotations
in Python in most circumstances. The runtime cost for defining annotations is
minimized, but it remains possible to introspect annotations at runtime.
It is 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.STRING` 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', owner=<function func at 0x...>)}
   >>> get_annotations(func, format=Format.STRING)
   {'arg': 'Undefined'}

The :ref:`porting <whatsnew314-porting-annotations>` section contains guidance
on changes that may be needed due to these changes, though in the majority of
cases, code will continue working as-is.

(Contributed by Jelle Zijlstra in :pep:`749` and :gh:`119180`;
:pep:`649` was written by Larry Hastings.)

.. seealso::

   :pep:`649`
      Deferred Evaluation Of Annotations Using Descriptors
   :pep:`749`
      Implementing PEP 649


.. _whatsnew314-multiple-interpreters:

:pep:`734`: Multiple interpreters in the standard library
---------------------------------------------------------

The CPython runtime supports running multiple copies of Python in the
same process simultaneously and has done so for over 20 years.
Each of these separate copies is called an 'interpreter'.
However, the feature had been available only through
the :ref:`C-API <sub-interpreter-support>`.

That limitation is removed in Python 3.14,
with the new :mod:`concurrent.interpreters` module.

There are at least two notable reasons why using multiple interpreters
has significant benefits:

* they support a new (to Python), human-friendly concurrency model
* true multi-core parallelism

For some use cases, concurrency in software improves efficiency and
can simplify design, at a high level.
At the same time, implementing and maintaining all but the simplest concurrency
is often a struggle for the human brain.
That especially applies to plain threads (for example, :mod:`threading`),
where all memory is shared between all threads.

With multiple isolated interpreters, you can take advantage of a class
of concurrency models, like Communicating Sequential Processes (CSP)
or the actor model, that have found
success in other programming languages, like Smalltalk, Erlang,
Haskell, and Go. Think of multiple interpreters as threads
but with opt-in sharing.

Regarding multi-core parallelism: as of Python 3.12, interpreters
are now sufficiently isolated from one another to be used in parallel
(see :pep:`684`). This unlocks a variety of CPU-intensive use cases
for Python that were limited by the :term:`GIL`.

Using multiple interpreters is similar in many ways to
:mod:`multiprocessing`, in that they both provide isolated logical
"processes" that can run in parallel, with no sharing by default.
However, when using multiple interpreters, an application will use
fewer system resources and will operate more efficiently (since it
stays within the same process). Think of multiple interpreters as
having the isolation of processes with the efficiency of threads.

.. XXX Add an example or two.
.. XXX Link to the not-yet-added HOWTO doc.

While the feature has been around for decades, multiple interpreters
have not been used widely, due to low awareness and the lack of a
standard library module. Consequently, they currently have several
notable limitations, which are expected to improve significantly now
that the feature is going mainstream.

Current limitations:

* starting each interpreter has not been optimized yet
* each interpreter uses more memory than necessary
  (work continues on extensive internal sharing between interpreters)
* there aren't many options *yet* for truly sharing objects or other
  data between interpreters (other than :type:`memoryview`)
* many third-party extension modules on PyPI are not yet compatible
  with multiple interpreters
  (all standard library extension modules *are* compatible)
* the approach to writing applications that use multiple isolated
  interpreters is mostly unfamiliar to Python users, for now

The impact of these limitations will depend on future CPython
improvements, how interpreters are used, and what the community solves
through PyPI packages. Depending on the use case, the limitations may
not have much impact, so try it out!

Furthermore, future CPython releases will reduce or eliminate overhead
and provide utilities that are less appropriate on PyPI. In the
meantime, most of the limitations can also be addressed through
extension modules, meaning PyPI packages can fill any gap for 3.14, and
even back to 3.12 where interpreters were finally properly isolated and
stopped sharing the :term:`GIL`. Likewise, libraries on PyPI are expected
to emerge for high-level abstractions on top of interpreters.

Regarding extension modules, work is in progress to update some PyPI
projects, as well as tools like Cython, pybind11, nanobind, and PyO3.
The steps for isolating an extension module are found at
:ref:`isolating-extensions-howto`.
Isolating a module has a lot of overlap with what is required to support
:ref:`free-threading <whatsnew314-free-threaded-cpython>`, so the ongoing
work in the community in that area will help accelerate support
for multiple interpreters.

Also added in 3.14: :ref:`concurrent.futures.InterpreterPoolExecutor
<whatsnew314-concurrent-futures-interp-pool>`.

(Contributed by Eric Snow in :gh:`134939`.)

.. seealso:: :pep:`734`


.. _whatsnew314-template-string-literals:

:pep:`750`: Template string literals
------------------------------------

Template strings are a new mechanism for custom string processing.
They share the familiar syntax of f-strings but, unlike f-strings,
return an object representing the static and interpolated parts of
the string, instead of a simple :class:`str`.

To write a t-string, use a ``'t'`` prefix instead of an ``'f'``:

.. doctest::

   >>> variety = 'Stilton'
   >>> template = t'Try some {variety} cheese!'
   >>> type(template)
   <class 'string.templatelib.Template'>

:class:`~string.templatelib.Template` objects provide access to the static
and interpolated (in curly braces) parts of a string *before* they are combined.
Iterate over :class:`!Template` instances to access their parts in order:

.. testsetup::

   variety = 'Stilton'
   template = t'Try some {variety} cheese!'

.. doctest::

   >>> list(template)
   ['Try some ', Interpolation('Stilton', 'variety', None, ''), ' cheese!']

It's easy to write (or call) code to process :class:`!Template` instances.
For example, here's a function that renders static parts lowercase and
:class:`~string.templatelib.Interpolation` instances uppercase:

.. code-block:: python

   from string.templatelib import Interpolation

   def lower_upper(template):
       """Render static parts lowercase and interpolations uppercase."""
       parts = []
       for part in template:
           if isinstance(part, Interpolation):
               parts.append(str(part.value).upper())
           else:
               parts.append(part.lower())
       return ''.join(parts)

   name = 'Wenslydale'
   template = t'Mister {name}'
   assert lower_upper(template) == 'mister WENSLYDALE'

Because :class:`!Template` instances distinguish between static strings and
interpolations at runtime, they can be useful for sanitising user input.
Writing a :func:`!html` function that escapes user input in HTML is an exercise
left to the reader!
Template processing code can provide improved flexibility.
For instance, a more advanced :func:`!html` function could accept
a :class:`!dict` of HTML attributes directly in the template:

.. code-block:: python

   attributes = {'src': 'limburger.jpg', 'alt': 'lovely cheese'}
   template = t'<img {attributes}>'
   assert html(template) == '<img src="limburger.jpg" alt="lovely cheese" />'

Of course, template processing code does not need to return a string-like result.
An even *more* advanced :func:`!html` could return a custom type representing
a DOM-like structure.

With t-strings in place, developers can write systems that sanitise SQL,
make safe shell operations, improve logging, tackle modern ideas in web
development (HTML, CSS, and so on), and implement lightweight custom business DSLs.

(Contributed by Jim Baker, Guido van Rossum, Paul Everitt, Koudai Aono,
Lysandros Nikolaou, Dave Peck, Adam Turner, Jelle Zijlstra, Bénédikt Tran,
and Pablo Galindo Salgado in :gh:`132661`.)

.. seealso:: :pep:`750`.


.. _whatsnew314-remote-debugging:

:pep:`768`: Safe external debugger interface
--------------------------------------------

Python 3.14 introduces a zero-overhead debugging interface that allows
debuggers and profilers to safely attach to running Python processes
without stopping or restarting them.
This is a significant enhancement to Python's debugging capabilities,
meaning that unsafe alternatives are no longer required.

The new interface provides safe execution points for attaching debugger code
without modifying the interpreter's normal execution path
or adding any overhead at runtime.
Due to this, tools can now inspect and interact with Python applications
in real-time, which is a crucial capability for high-availability systems
and production environments.

For convenience, this interface is implemented in the :func:`sys.remote_exec`
function. For example:

.. code-block:: python

   import sys
   from tempfile import NamedTemporaryFile

   with NamedTemporaryFile(mode='w', suffix='.py', delete=False) as f:
       script_path = f.name
       f.write(f'import my_debugger; my_debugger.connect({os.getpid()})')

   # Execute in process with PID 1234
   print('Behold! An offering:')
   sys.remote_exec(1234, script_path)


This function allows sending Python code to be executed in a target process
at the next safe execution point.
However, tool authors can also implement the protocol directly as described
in the PEP, which details the underlying mechanisms used to safely attach to
running processes.

The debugging interface has been carefully designed with security in mind
and includes several mechanisms to control access:

* A :envvar:`PYTHON_DISABLE_REMOTE_DEBUG` environment variable.
* A :option:`-X disable-remote-debug` command-line option.
* A :option:`--without-remote-debug` configure flag to completely disable
  the feature at build time.

(Contributed by Pablo Galindo Salgado, Matt Wozniski, and Ivona Stojanovic
in :gh:`131591`.)

.. seealso:: :pep:`768`.


.. _whatsnew314-tail-call-interpreter:

A new type of interpreter
-------------------------

A new type of interpreter has been added to CPython.
It uses tail calls between small C functions that implement individual
Python opcodes, rather than one large C ``case`` statement.
For certain newer compilers, this interpreter provides
significantly better performance. Preliminary benchmarks suggest a geometric
mean of 3-5% faster on the standard ``pyperformance`` benchmark suite,
depending on platform and architecture.
The baseline is Python 3.14 built with Clang 19, without this new interpreter.

This interpreter currently only works with Clang 19 and newer
on x86-64 and AArch64 architectures.
However, a future release of GCC is expected to support this as well.

This feature is opt-in for now. Enabling profile-guided optimization is highly
recommendeded when using the new interpreter as it is the only configuration
that has been tested and validated for improved performance.
For further information, see :option:`--with-tail-call-interp`.

.. note::

   This is not to be confused with `tail call optimization`__ of Python
   functions, which is currently not implemented in CPython.

   This new interpreter type is an internal implementation detail of the CPython
   interpreter.  It doesn't change the visible behavior of Python programs at
   all.  It can improve their performance, but doesn't change anything else.

   __ https://en.wikipedia.org/wiki/Tail_call

(Contributed by Ken Jin in :gh:`128563`, with ideas on how to implement this
in CPython by Mark Shannon, Garrett Gu, Haoran Xu, and Josh Haberman.)


.. _whatsnew314-free-threaded-cpython:

Free-threaded mode improvements
-------------------------------

CPython's free-threaded mode (:pep:`703`), initially added in 3.13,
has been significantly improved in Python 3.14.
The implementation described in PEP 703 has been finished, including C API
changes, and temporary workarounds in the interpreter were replaced with
more permanent solutions.
The specializing adaptive interpreter (:pep:`659`) is now enabled
in free-threaded mode, which along with many other optimizations
greatly improves its performance.
The performance penalty on single-threaded code in free-threaded mode
is now roughly 5-10%, depending on the platform and C compiler used.

From Python 3.14, when compiling extension modules for the free-threaded build of
CPython on Windows, the preprocessor variable ``Py_GIL_DISABLED`` now needs to
be specified by the build backend, as it will no longer be determined
automatically by the C compiler. For a running interpreter, the setting that
was used at compile time can be found using :func:`sysconfig.get_config_var`.

The new :option:`-X context_aware_warnings <-X>` flag controls if
:ref:`concurrent safe warnings control <whatsnew314-concurrent-warnings-control>`
is enabled. The flag defaults to true for the free-threaded build
and false for the GIL-enabled build.

A new :data:`~sys.flags.thread_inherit_context` flag has been added,
which if enabled means that threads created with :class:`threading.Thread`
start with a copy of the :class:`~contextvars.Context()` of the caller of
:meth:`~threading.Thread.start`.  Most significantly, this makes the warning
filtering context established by :class:`~warnings.catch_warnings` be
"inherited" by threads (or asyncio tasks) started within that context.  It also
affects other modules that use context variables, such as the :mod:`decimal`
context manager.
This flag defaults to true for the free-threaded build and false for
the GIL-enabled build.

(Contributed by Sam Gross, Matt Page, Neil Schemenauer, Thomas Wouters,
Donghee Na, Kirill Podoprigora, Ken Jin, Itamar Oren, Brett Simmers,
Dino Viehland, Nathan Goldbaum, Ralf Gommers, Lysandros Nikolaou, Kumar Aditya,
Edgar Margffoy, and many others.
Some of these contributors are employed by Meta, which has continued to provide
significant engineering resources to support this project.)


.. _whatsnew314-improved-error-messages:

Improved error messages
-----------------------

* The interpreter now provides helpful suggestions when it detects typos in Python
  keywords. When a word that closely resembles a Python keyword is encountered,
  the interpreter will suggest the correct keyword in the error message. This
  feature helps programmers quickly identify and fix common typing mistakes. For
  example:

  .. code-block:: pycon

     >>> whille True:
     ...     pass
     Traceback (most recent call last):
       File "<stdin>", line 1
         whille True:
         ^^^^^^
     SyntaxError: invalid syntax. Did you mean 'while'?

  While the feature focuses on the most common cases, some variations of
  misspellings may still result in regular syntax errors.
  (Contributed by Pablo Galindo in :gh:`132449`.)

* :keyword:`elif` statements that follow an :keyword:`else` block now have
  a specific error message.
  (Contributed by Steele Farnsworth in :gh:`129902`.)

  .. code-block:: pycon

      >>> if who == "me":
      ...     print("It's me!")
      ... else:
      ...     print("It's not me!")
      ... elif who is None:
      ...     print("Who is it?")
      File "<stdin>", line 5
        elif who is None:
        ^^^^
      SyntaxError: 'elif' block follows an 'else' block

* If a statement is passed to the :ref:`if_expr` after :keyword:`else`,
  or one of :keyword:`pass`, :keyword:`break`, or :keyword:`continue`
  is passed before :keyword:`if`, then the
  error message highlights where the :token:`~python-grammar:expression` is
  required. (Contributed by Sergey Miryanov in :gh:`129515`.)

  .. code-block:: pycon

     >>> x = 1 if True else pass
     Traceback (most recent call last):
       File "<string>", line 1
         x = 1 if True else pass
                            ^^^^
     SyntaxError: expected expression after 'else', but statement is given

     >>> x = continue if True else break
     Traceback (most recent call last):
       File "<string>", line 1
         x = continue if True else break
             ^^^^^^^^
     SyntaxError: expected expression before 'if', but statement is given

* When incorrectly closed strings are detected, the error message suggests
  that the string may be intended to be part of the string.
  (Contributed by Pablo Galindo in :gh:`88535`.)

  .. code-block:: pycon

    >>> "The interesting object "The important object" is very important"
    Traceback (most recent call last):
    SyntaxError: invalid syntax. Is this intended to be part of the string?

* When strings have incompatible prefixes, the error now shows
  which prefixes are incompatible.
  (Contributed by Nikita Sobolev in :gh:`133197`.)

  .. code-block:: pycon

    >>> ub'abc'
      File "<python-input-0>", line 1
        ub'abc'
        ^^
    SyntaxError: 'u' and 'b' prefixes are incompatible

* Improved error messages when using ``as`` with incompatible targets in:

  - Imports: ``import ... as ...``
  - From imports: ``from ... import ... as ...``
  - Except handlers: ``except ... as ...``
  - Pattern-match cases: ``case ... as ...``

  (Contributed by Nikita Sobolev in :gh:`123539`, :gh:`123562`, and :gh:`123440`.)

* Improved error message when trying to add an instance of an unhashable type to
  a :class:`dict` or :class:`set`.
  (Contributed by CF Bolz-Tereick and Victor Stinner in :gh:`132828`.)

  .. code-block:: pycon

     >>> s = set()
     >>> s.add({'pages': 12, 'grade': 'A'})
     Traceback (most recent call last):
       File "<python-input-1>", line 1, in <module>
         s.add({'pages': 12, 'grade': 'A'})
         ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     TypeError: cannot use 'dict' as a set element (unhashable type: 'dict')
     >>> d = {}
     >>> l = [1, 2, 3]
     >>> d[l] = 12
     Traceback (most recent call last):
       File "<python-input-4>", line 1, in <module>
         d[l] = 12
         ~^^^
     TypeError: cannot use 'list' as a dict key (unhashable type: 'list')

* Improved error message when an object supporting the synchronous
  context manager protocol is entered using :keyword:`async with`
  instead of :keyword:`with`,
  and vice versa for the asynchronous context manager protocol.
  (Contributed by Bénédikt Tran in :gh:`128398`.)


.. _whatsnew314-zstandard:

:pep:`784`: Zstandard support in the standard library
-----------------------------------------------------

The new :mod:`!compression` package contains modules :mod:`!compression.lzma`,
:mod:`!compression.bz2`, :mod:`!compression.gzip` and :mod:`!compression.zlib`
which re-export the :mod:`lzma`, :mod:`bz2`, :mod:`gzip` and :mod:`zlib`
modules respectively. The new import names under :mod:`!compression` are the
preferred names for importing these compression modules from Python 3.14. However,
the existing modules names have not been deprecated. Any deprecation or removal
of the existing compression modules will occur no sooner than five years after
the release of 3.14.

The new :mod:`!compression.zstd` module provides compression and decompression
APIs for the Zstandard format via bindings to `Meta's zstd library
<https://facebook.github.io/zstd/>`__. Zstandard is a widely adopted, highly
efficient, and fast compression format. In addition to the APIs introduced in
:mod:`!compression.zstd`, support for reading and writing Zstandard compressed
archives has been added to the :mod:`tarfile`, :mod:`zipfile`, and
:mod:`shutil` modules.

Here's an example of using the new module to compress some data:

.. code-block:: python

    from compression import zstd
    import math

    data = str(math.pi).encode() * 20
    compressed = zstd.compress(data)
    ratio = len(compressed) / len(data)
    print(f"Achieved compression ratio of {ratio}")

As can be seen, the API is similar to the APIs of the :mod:`!lzma` and
:mod:`!bz2` modules.

(Contributed by Emma Harper Smith, Adam Turner, Gregory P. Smith, Tomas Roun,
Victor Stinner, and Rogdham in :gh:`132983`.)

.. seealso:: :pep:`784`.


.. _whatsnew314-asyncio-introspection:

Asyncio introspection capabilities
----------------------------------

Added a new command-line interface to inspect running Python processes
using asynchronous tasks, available via ``python -m asyncio ps PID``
or ``python -m asyncio pstree PID``.

The ``ps`` subcommand inspects the given process ID (PID) and displays
information about currently running asyncio tasks.
It outputs a task table: a flat listing of all tasks, their names,
their coroutine stacks, and which tasks are awaiting them.


The ``pstree`` subcommand fetches the same information, but instead renders a
visual async call tree, showing coroutine relationships in a hierarchical format.
This command is particularly useful for debugging long-running or stuck
asynchronous programs.
It can help developers quickly identify where a program is blocked,
what tasks are pending, and how coroutines are chained together.

For example given this code:

.. code-block:: python

  import asyncio

  async def play_track(track):
      await asyncio.sleep(5)
      print(f'🎵 Finished: {track}')

  async def play_album(name, tracks):
      async with asyncio.TaskGroup() as tg:
          for track in tracks:
              tg.create_task(play_track(track), name=track)

  async def main():
      async with asyncio.TaskGroup() as tg:
          tg.create_task(
            play_album('Sundowning', ['TNDNBTG', 'Levitate']),
            name='Sundowning')
          tg.create_task(
            play_album('TMBTE', ['DYWTYLM', 'Aqua Regia']),
            name='TMBTE')

  if __name__ == '__main__':
      asyncio.run(main())

Executing the new tool on the running process will yield a table like this:

.. code-block:: bash

  python -m asyncio ps 12345

  tid        task id              task name            coroutine stack                                    awaiter chain                                      awaiter name    awaiter id
  ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  1935500    0x7fc930c18050       Task-1               TaskGroup._aexit -> TaskGroup.__aexit__ -> main                                                                       0x0
  1935500    0x7fc930c18230       Sundowning           TaskGroup._aexit -> TaskGroup.__aexit__ -> album   TaskGroup._aexit -> TaskGroup.__aexit__ -> main    Task-1          0x7fc930c18050
  1935500    0x7fc93173fa50       TMBTE                TaskGroup._aexit -> TaskGroup.__aexit__ -> album   TaskGroup._aexit -> TaskGroup.__aexit__ -> main    Task-1          0x7fc930c18050
  1935500    0x7fc93173fdf0       TNDNBTG              sleep -> play                                      TaskGroup._aexit -> TaskGroup.__aexit__ -> album   Sundowning      0x7fc930c18230
  1935500    0x7fc930d32510       Levitate             sleep -> play                                      TaskGroup._aexit -> TaskGroup.__aexit__ -> album   Sundowning      0x7fc930c18230
  1935500    0x7fc930d32890       DYWTYLM              sleep -> play                                      TaskGroup._aexit -> TaskGroup.__aexit__ -> album   TMBTE           0x7fc93173fa50
  1935500    0x7fc93161ec30       Aqua Regia           sleep -> play                                      TaskGroup._aexit -> TaskGroup.__aexit__ -> album   TMBTE           0x7fc93173fa50

or a tree like this:

.. code-block:: bash

  python -m asyncio pstree 12345

  └── (T) Task-1
      └──  main example.py:13
          └──  TaskGroup.__aexit__ Lib/asyncio/taskgroups.py:72
              └──  TaskGroup._aexit Lib/asyncio/taskgroups.py:121
                  ├── (T) Sundowning
                  │   └──  album example.py:8
                  │       └──  TaskGroup.__aexit__ Lib/asyncio/taskgroups.py:72
                  │           └──  TaskGroup._aexit Lib/asyncio/taskgroups.py:121
                  │               ├── (T) TNDNBTG
                  │               │   └──  play example.py:4
                  │               │       └──  sleep Lib/asyncio/tasks.py:702
                  │               └── (T) Levitate
                  │                   └──  play example.py:4
                  │                       └──  sleep Lib/asyncio/tasks.py:702
                  └── (T) TMBTE
                      └──  album example.py:8
                          └──  TaskGroup.__aexit__ Lib/asyncio/taskgroups.py:72
                              └──  TaskGroup._aexit Lib/asyncio/taskgroups.py:121
                                  ├── (T) DYWTYLM
                                  │   └──  play example.py:4
                                  │       └──  sleep Lib/asyncio/tasks.py:702
                                  └── (T) Aqua Regia
                                      └──  play example.py:4
                                          └──  sleep Lib/asyncio/tasks.py:702

If a cycle is detected in the async await graph (which could indicate a
programming issue), the tool raises an error and lists the cycle paths that
prevent tree construction:

.. code-block:: bash

  python -m asyncio pstree 12345

  ERROR: await-graph contains cycles - cannot print a tree!

  cycle: Task-2 → Task-3 → Task-2

(Contributed by Pablo Galindo, Łukasz Langa, Yury Selivanov, and Marta
Gomez Macias in :gh:`91048`.)


.. _whatsnew314-concurrent-warnings-control:

Concurrent safe warnings control
--------------------------------

The :class:`warnings.catch_warnings` context manager will now optionally
use a context variable for warning filters. This is enabled by setting
the :data:`~sys.flags.context_aware_warnings` flag, either with the ``-X``
command-line option or an environment variable. This gives predictable
warnings control when using :class:`~warnings.catch_warnings` combined with
multiple threads or asynchronous tasks. The flag defaults to true for the
free-threaded build and false for the GIL-enabled build.

(Contributed by Neil Schemenauer and Kumar Aditya in :gh:`130010`.)


Other language changes
======================

* All Windows code pages are now supported as 'cpXXX' codecs on Windows.
  (Contributed by Serhiy Storchaka in :gh:`123803`.)

* Implement mixed-mode arithmetic rules combining real and complex numbers
  as specified by the C standard since C99.
  (Contributed by Sergey B Kirpichev in :gh:`69639`.)

* More syntax errors are now detected regardless of optimisation and
  the :option:`-O` command-line option.
  This includes writes to ``__debug__``, incorrect use of :keyword:`await`,
  and asynchronous comprehensions outside asynchronous functions.
  For example, ``python -O -c 'assert (__debug__ := 1)'``
  or ``python -O -c 'assert await 1'`` now produce :exc:`SyntaxError`\ s.
  (Contributed by Irit Katriel and Jelle Zijlstra in :gh:`122245` & :gh:`121637`.)

* When subclassing a pure C type, the C slots for the new type
  are no longer replaced with a wrapped version on class creation
  if they are not explicitly overridden in the subclass.
  (Contributed by Tomasz Pytel in :gh:`132284`.)


Built-ins
---------

* The :meth:`bytes.fromhex` and :meth:`bytearray.fromhex` methods now accept
  ASCII :class:`bytes` and :term:`bytes-like objects <bytes-like object>`.
  (Contributed by Daniel Pope in :gh:`129349`.)

* Add 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 a :exc:`TypeError` if the argument is not a real number.
  (Contributed by Serhiy Storchaka in :gh:`84978`.)

* Support underscore and comma as thousands separators in the fractional part
  for floating-point presentation types of the new-style string formatting
  (with :func:`format` or :ref:`f-strings`).
  (Contributed by Sergey B Kirpichev in :gh:`87790`.)

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

* The :func:`map` function now has an optional keyword-only *strict* flag
  like :func:`zip` to check that all the iterables are of equal length.
  (Contributed by Wannes Boeykens in :gh:`119793`.)

* The :class:`memoryview` type now supports subscription,
  making it a :term:`generic type`.
  (Contributed by Brian Schubert in :gh:`126012`.)

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

* Three-argument :func:`pow` now tries calling :meth:`~object.__rpow__`
  if necessary.
  Previously it was only called in two-argument :func:`!pow`
  and the binary power operator.
  (Contributed by Serhiy Storchaka in :gh:`130104`.)

* :class:`super` objects are now :mod:`copyable <copy>` and :mod:`pickleable
  <pickle>`.
  (Contributed by Serhiy Storchaka in :gh:`125767`.)


Command line and environment
----------------------------

* The import time flag can now track modules that are already loaded ('cached'),
  via the new :option:`-X importtime=2 <-X>`.
  When such a module is imported, the ``self`` and ``cumulative`` times
  are replaced by the string ``cached``.

  Values above ``2`` for ``-X importtime`` are now reserved for future use.

  (Contributed by Noah Kim and Adam Turner in :gh:`118655`.)

* The command-line option :option:`-c` now automatically dedents its code
  argument before execution. The auto-dedentation behavior mirrors
  :func:`textwrap.dedent`.
  (Contributed by Jon Crall and Steven Sun in :gh:`103998`.)

* :option:`!-J` is no longer a reserved flag for Jython_,
  and now has no special meaning.
  (Contributed by Adam Turner in :gh:`133336`.)

  .. _Jython: https://www.jython.org/


.. _whatsnew314-bracketless-except:

PEP 758: Allow ``except`` and ``except*`` expressions without brackets
----------------------------------------------------------------------

The :keyword:`except` and :keyword:`except* <except_star>` expressions
now allow brackets to be omitted when there are multiple exception types
and the ``as`` clause is not used.
For example:

.. code-block:: python

   try:
       connect_to_server()
   except TimeoutError, ConnectionRefusedError:
       print('The network has ceased to be!')

(Contributed by Pablo Galindo and Brett Cannon in :pep:`758` and :gh:`131831`.)


.. _whatsnew314-finally-syntaxwarning:

PEP 765: Control flow in :keyword:`finally` blocks
--------------------------------------------------

The compiler now emits a :exc:`SyntaxWarning` when a :keyword:`return`,
:keyword:`break`, or :keyword:`continue` statement have the effect of
leaving a :keyword:`finally` block.
This change is specified in :pep:`765`.

In situations where this change is inconvenient (such as those where the
warnings are redundant due to code linting), the :ref:`warning filter
<warning-filter>` can be used to turn off all syntax warnings by adding
``ignore::SyntaxWarning`` as a filter. This can be specified in combination
with a filter that converts other warnings to errors (for example, passing
``-Werror -Wignore::SyntaxWarning`` as CLI options, or setting
``PYTHONWARNINGS=error,ignore::SyntaxWarning``).

Note that applying such a filter at runtime using the :mod:`warnings` module
will only suppress the warning in code that is compiled *after* the filter is
adjusted. Code that is compiled prior to the filter adjustment (for example,
when a module is imported) will still emit the syntax warning.

(Contributed by Irit Katriel in :gh:`130080`.)


.. _whatsnew314-incremental-gc:

Incremental garbage collection
------------------------------

The cycle garbage collector is now incremental.
This means that maximum pause times are reduced
by an order of magnitude or more for larger heaps.

There are now only two generations: young and old.
When :func:`gc.collect` is not called directly, the
GC is invoked a little less frequently. When invoked, it
collects the young generation and an increment of the
old generation, instead of collecting one or more generations.

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.

(Contributed by Mark Shannon in :gh:`108362`.)


Default interactive shell
-------------------------

.. _whatsnew314-pyrepl-highlighting:

* The default :term:`interactive` shell now highlights Python syntax.
  The feature is enabled by default, save if :envvar:`PYTHON_BASIC_REPL`
  or any other environment variable that disables colour is set.
  See :ref:`using-on-controlling-color` for details.

  The default color theme for syntax highlighting strives for good contrast
  and exclusively uses the 4-bit VGA standard ANSI color codes for maximum
  compatibility. The theme can be customized using an experimental API
  :func:`!_colorize.set_theme`.
  This can be called interactively or in the :envvar:`PYTHONSTARTUP` script.
  Note that this function has no stability guarantees,
  and may change or be removed.

  (Contributed by Łukasz Langa in :gh:`131507`.)

* The default :term:`interactive` shell now supports import auto-completion.
  This means that typing ``import co`` and pressing :kbd:`<Tab>` will suggest
  modules starting with ``co``. Similarly, typing ``from concurrent import i``
  will suggest submodules of ``concurrent`` starting with ``i``.
  Note that autocompletion of module attributes is not currently supported.
  (Contributed by Tomas Roun in :gh:`69605`.)


New modules
===========

* :mod:`annotationlib`:
  For introspecting :term:`annotations <annotation>`.
  See :ref:`PEP 749 <whatsnew314-deferred-annotations>` for more details.
  (Contributed by Jelle Zijlstra in :gh:`119180`.)

* :mod:`compression` (including :mod:`compression.zstd`):
  A package for compression-related modules,
  including a new module to support the Zstandard compression format.
  See :ref:`PEP 784 <whatsnew314-zstandard>` for more details.
  (Contributed by Emma Harper Smith, Adam Turner, Gregory P. Smith, Tomas Roun,
  Victor Stinner, and Rogdham in :gh:`132983`.)

* :mod:`concurrent.interpreters`:
  Support for multiple interpreters in the standard library.
  See :ref:`PEP 734 <whatsnew314-multiple-interpreters>` for more details.
  (Contributed by Eric Snow in :gh:`134939`.)

* :mod:`string.templatelib`:
  Support for template string literals (t-strings).
  See :ref:`PEP 750 <whatsnew314-template-string-literals>` for more details.
  (Contributed by Jim Baker, Guido van Rossum, Paul Everitt, Koudai Aono,
  Lysandros Nikolaou, Dave Peck, Adam Turner, Jelle Zijlstra, Bénédikt Tran,
  and Pablo Galindo Salgado in :gh:`132661`.)


Improved modules
================

argparse
--------

* The default value of the :ref:`program name <prog>` for
  :class:`argparse.ArgumentParser` now reflects the way the Python
  interpreter was instructed to find the ``__main__`` module code.
  (Contributed by Serhiy Storchaka and Alyssa Coghlan in :gh:`66436`.)

* Introduced the optional *suggest_on_error* parameter to
  :class:`argparse.ArgumentParser`, enabling suggestions for argument choices
  and subparser names if mistyped by the user.
  (Contributed by Savannah Ostrowski in :gh:`124456`.)

* Enable color for help text, which can be disabled with the optional *color*
  parameter to :class:`argparse.ArgumentParser`.
  This can also be controlled by :ref:`environment variables
  <using-on-controlling-color>`.
  (Contributed by Hugo van Kemenade in :gh:`130645`.)


ast
---

* Add :func:`~ast.compare`, a function for comparing two ASTs.
  (Contributed by Batuhan Taskaya and Jeremy Hylton in :gh:`60191`.)

* 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`.)

* The :func:`repr` output for AST nodes now includes more information.
  (Contributed by Tomas Roun in :gh:`116022`.)

* When called with an AST as input, the :func:`~ast.parse` function
  now always verifies that the root node type is appropriate.
  (Contributed by Irit Katriel in :gh:`130139`.)

* Add new options to the command-line interface:
  :option:`--feature-version <ast --feature-version>`,
  :option:`--optimize <ast --optimize>`, and
  :option:`--show-empty <ast --show-empty>`.
  (Contributed by Semyon Moroz in :gh:`133367`.)


asyncio
-------

* The function and methods named :func:`!create_task` now take an arbitrary
  list of keyword arguments. All keyword arguments are passed to the
  :class:`~asyncio.Task` constructor or the custom task factory.
  (See :meth:`~asyncio.loop.set_task_factory` for details.)
  The ``name`` and ``context`` keyword arguments are no longer special;
  the name should now be set using the ``name`` keyword argument of the factory,
  and ``context`` may be ``None``.

  This affects the following function and methods:
  :meth:`asyncio.create_task`,
  :meth:`asyncio.loop.create_task`,
  :meth:`asyncio.TaskGroup.create_task`.

  (Contributed by Thomas Grainger in :gh:`128307`.)

* There are two new utility functions for
  introspecting and printing a program's call graph:
  :func:`~asyncio.capture_call_graph` and :func:`~asyncio.print_call_graph`.
  See :ref:`Asyncio introspection capabilities
  <whatsnew314-asyncio-introspection>` for more details.
  (Contributed by Yury Selivanov, Pablo Galindo Salgado, and Łukasz Langa
  in :gh:`91048`.)


calendar
--------

.. _whatsnew314-color-calendar:

* By default, today's date is highlighted in color in :mod:`calendar`'s
  :ref:`command-line <calendar-cli>` text output.
  This can be controlled by :ref:`environment variables
  <using-on-controlling-color>`.
  (Contributed by Hugo van Kemenade in :gh:`128317`.)


concurrent.futures
------------------

.. _whatsnew314-concurrent-futures-interp-pool:

* Add a new executor class, :class:`~concurrent.futures.InterpreterPoolExecutor`,
  which exposes multiple Python interpreters in the same process
  ('subinterpreters') to Python code.
  This uses a pool of independent Python interpreters to execute calls
  asynchronously.

  This is separate from the new :mod:`~concurrent.interpreters` module
  introduced by :ref:`PEP 734 <whatsnew314-multiple-interpreters>`.
  (Contributed by Eric Snow in :gh:`124548`.)

.. _whatsnew314-concurrent-futures-start-method:

* On Unix platforms other than macOS, :ref:`'forkserver'
  <multiprocessing-start-method-forkserver>` is now the default :ref:`start
  method <multiprocessing-start-methods>` for
  :class:`~concurrent.futures.ProcessPoolExecutor`
  (replacing :ref:`'fork' <multiprocessing-start-method-fork>`).
  This change does not affect Windows or macOS, where :ref:`'spawn'
  <multiprocessing-start-method-spawn>` remains the default start method.

  If the threading incompatible *fork* method is required, you must explicitly
  request it by supplying a multiprocessing context *mp_context* to
  :class:`~concurrent.futures.ProcessPoolExecutor`.

  See :ref:`forkserver restrictions <multiprocessing-programming-forkserver>`
  for information and differences with the *fork* method and how this change
  may affect existing code with mutable global shared variables and/or shared
  objects that can not be automatically :mod:`pickled <pickle>`.

  (Contributed by Gregory P. Smith in :gh:`84559`.)

* Add two new methods to :class:`~concurrent.futures.ProcessPoolExecutor`,
  :meth:`~concurrent.futures.ProcessPoolExecutor.terminate_workers`
  and :meth:`~concurrent.futures.ProcessPoolExecutor.kill_workers`,
  as ways to terminate or kill all living worker processes in the given pool.
  (Contributed by Charles Machalow in :gh:`130849`.)

* Add the optional *buffersize* parameter to :meth:`Executor.map
  <concurrent.futures.Executor.map>` to limit the number of submitted
  tasks whose results have not yet been yielded. If the buffer is full,
  iteration over the *iterables* pauses until a result is yielded from the
  buffer.
  (Contributed by Enzo Bonnal and Josh Rosenberg in :gh:`74028`.)


configparser
------------

* :mod:`!configparser` will no longer write config files it cannot read,
  to improve security.
  Attempting to :meth:`~configparser.ConfigParser.write` keys containing
  delimiters or beginning with the section header pattern will raise an
  :class:`~configparser.InvalidWriteError`.
  (Contributed by Jacob Lincoln in :gh:`129270`.)


contextvars
-----------

* Support the :term:`context manager` protocol
  for :class:`~contextvars.Token` objects.
  (Contributed by Andrew Svetlov in :gh:`129889`.)


ctypes
------

* The layout of :ref:`bit fields <ctypes-bit-fields-in-structures-unions>`
  in :class:`~ctypes.Structure` and :class:`~ctypes.Union` objects
  is now a closer match to platform defaults (GCC/Clang or MSVC).
  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`.)

* The class of :class:`~ctypes.Structure`/:class:`~ctypes.Union`
  field descriptors is now available as :class:`~ctypes.CField`,
  and has new attributes to aid debugging and introspection.
  (Contributed by Petr Viktorin in :gh:`128715`.)

* On Windows, the :exc:`~ctypes.COMError` exception is now public.
  (Contributed by Jun Komoda in :gh:`126686`.)

* On Windows, the :func:`~ctypes.CopyComPointer` function is now public.
  (Contributed by Jun Komoda in :gh:`127275`.)

* Add :func:`~ctypes.memoryview_at`, a function to create a
  :class:`memoryview` object that refers to the supplied pointer and
  length. This works like :func:`ctypes.string_at` except it avoids a
  buffer copy, and is typically useful when implementing pure Python
  callback functions that are passed dynamically-sized buffers.
  (Contributed by Rian Hunter in :gh:`112018`.)

* Complex types, :class:`~ctypes.c_float_complex`,
  :class:`~ctypes.c_double_complex`, and :class:`~ctypes.c_longdouble_complex`,
  are now available if both the compiler and the ``libffi`` library support
  complex C types.
  (Contributed by Sergey B Kirpichev in :gh:`61103`.)

* Add :func:`ctypes.util.dllist` for listing the shared libraries
  loaded by the current process.
  (Contributed by Brian Ward in :gh:`119349`.)

* Move :func:`ctypes.POINTER` types cache from a global internal cache
  (``_pointer_type_cache``) to the :attr:`_CData.__pointer_type__
  <ctypes._CData.__pointer_type__>` attribute of the corresponding
  :mod:`!ctypes` types.
  This will stop the cache from growing without limits in some situations.
  (Contributed by Sergey Miryanov in :gh:`100926`.)

* The :class:`~ctypes.py_object` type now supports subscription,
  making it a :term:`generic type`.
  (Contributed by Brian Schubert in :gh:`132168`.)

* :mod:`!ctypes` now supports :term:`free-threading builds <free threading>`.
  (Contributed by Kumar Aditya and Peter Bierma in :gh:`127945`.)


curses
------

* Add the :func:`~curses.assume_default_colors` function,
  a refinement of the :func:`~curses.use_default_colors` function which
  allows changing the color pair ``0``.
  (Contributed by Serhiy Storchaka in :gh:`133139`.)


datetime
--------

* Add the :meth:`~datetime.date.strptime` method to the
  :class:`datetime.date` and :class:`datetime.time` classes.
  (Contributed by Wannes Boeykens in :gh:`41431`.)


decimal
-------

* Add :meth:`.Decimal.from_number` as an alternative constructor for
  :class:`~decimal.Decimal`.
  (Contributed by Serhiy Storchaka in :gh:`121798`.)

* Expose :func:`~decimal.IEEEContext` to support creation of contexts
  corresponding to the IEEE 754 (2008) decimal interchange formats.
  (Contributed by Sergey B Kirpichev in :gh:`53032`.)


difflib
-------

* Comparison pages with highlighted changes generated by the
  :class:`~difflib.HtmlDiff` class now support 'dark mode'.
  (Contributed by Jiahao Li in :gh:`129939`.)


dis
---

* Add 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`
  - :func:`dis.disassemble`

  This feature is also exposed via :option:`dis --show-positions`.
  (Contributed by Bénédikt Tran in :gh:`123165`.)

* Add the :option:`dis --specialized` command-line option to
  show specialized bytecode.
  (Contributed by Bénédikt Tran in :gh:`127413`.)


errno
-----

* Add the :data:`~errno.EHWPOISON` error code constant.
  (Contributed by James Roy in :gh:`126585`.)


faulthandler
------------

* Add support for printing the C stack trace on systems that
  :ref:`support it <c-stack-compatibility>` via the new
  :func:`~faulthandler.dump_c_stack` function or via the *c_stack* argument
  in :func:`faulthandler.enable`.
  (Contributed by Peter Bierma in :gh:`127604`.)


fnmatch
-------

* Add :func:`~fnmatch.filterfalse`, a function to reject names
  matching a given pattern.
  (Contributed by Bénédikt Tran in :gh:`74598`.)


fractions
---------

* A :class:`~fractions.Fraction` object may now be constructed from any
  object with the :meth:`!as_integer_ratio` method.
  (Contributed by Serhiy Storchaka in :gh:`82017`.)

* Add :meth:`.Fraction.from_number` as an alternative constructor for
  :class:`~fractions.Fraction`.
  (Contributed by Serhiy Storchaka in :gh:`121797`.)


functools
---------

* Add the :data:`~functools.Placeholder` sentinel.
  This may be used with the :func:`~functools.partial`
  or :func:`~functools.partialmethod` functions to reserve a place
  for positional arguments in the returned :ref:`partial object
  <partial-objects>`.
  (Contributed by Dominykas Grigonis in :gh:`119127`.)

* Allow the *initial* parameter of :func:`~functools.reduce` to be passed
  as a keyword argument.
  (Contributed by Sayandip Dutta in :gh:`125916`.)


getopt
------

* Add support for options with optional arguments.
  (Contributed by Serhiy Storchaka in :gh:`126374`.)

* Add support for returning intermixed options and non-option arguments in order.
  (Contributed by Serhiy Storchaka in :gh:`126390`.)


getpass
-------

* Support keyboard feedback in the :func:`~getpass.getpass` function via
  the keyword-only optional argument *echo_char*.
  Placeholder characters are rendered whenever a character is entered,
  and removed when a character is deleted.
  (Contributed by Semyon Moroz in :gh:`77065`.)


graphlib
--------

* Allow :meth:`.TopologicalSorter.prepare` to be called more than once
  as long as sorting has not started.
  (Contributed by Daniel Pope in :gh:`130914`.)


heapq
-----

* The :mod:`!heapq` module has improved support for working with max-heaps,
  via the following new functions:

  * :func:`~heapq.heapify_max`
  * :func:`~heapq.heappush_max`
  * :func:`~heapq.heappop_max`
  * :func:`~heapq.heapreplace_max`
  * :func:`~heapq.heappushpop_max`


hmac
----

* Add a built-in implementation for HMAC (:rfc:`2104`) using formally verified
  code from the `HACL* <https://github.com/hacl-star/hacl-star/>`__ project.
  This implementation is used as a fallback when the OpenSSL implementation
  of HMAC is not available.
  (Contributed by Bénédikt Tran in :gh:`99108`.)


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`.)

* The :mod:`http.server` module now supports serving over HTTPS using the
  :class:`http.server.HTTPSServer` class. This functionality is exposed by
  the command-line interface (``python -m http.server``) through the following
  options:

  * :option:`--tls-cert \<path\> <http.server --tls-cert>`:
    Path to the TLS certificate file.
  * :option:`--tls-key \<path\> <http.server --tls-key>`:
    Optional path to the private key file.
  * :option:`--tls-password-file \<path\> <http.server --tls-password-file>`:
    Optional path to the password file for the private key.

  (Contributed by Semyon Moroz in :gh:`85162`.)


imaplib
-------

* Add :meth:`.IMAP4.idle`, implementing the IMAP4
  ``IDLE`` command as defined in :rfc:`2177`.
  (Contributed by Forest in :gh:`55454`.)


inspect
-------

* :func:`~inspect.signature` takes a new argument *annotation_format* to control
  the :class:`annotationlib.Format` used for representing annotations.
  (Contributed by Jelle Zijlstra in :gh:`101552`.)

* :meth:`.Signature.format` takes a new argument *unquote_annotations*.
  If true, string :term:`annotations <annotation>` are displayed without
  surrounding quotes.
  (Contributed by Jelle Zijlstra in :gh:`101552`.)

* Add function :func:`~inspect.ispackage` to determine whether an object is a
  :term:`package` or not.
  (Contributed by Zhikang Yan in :gh:`125634`.)


io
--

* Reading text from a non-blocking stream with ``read`` may now raise a
  :exc:`BlockingIOError` if the operation cannot immediately return bytes.
  (Contributed by Giovanni Siragusa in :gh:`109523`.)

* Add the :class:`~io.Reader` and :class:`~io.Writer` protocols as simpler
  alternatives to the pseudo-protocols :class:`typing.IO`,
  :class:`typing.TextIO`, and :class:`typing.BinaryIO`.
  (Contributed by Sebastian Rittau in :gh:`127648`.)


json
----

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

* Allow using the :mod:`json` module as a script using the :option:`-m` switch:
  :program:`python -m json`.
  This is now preferred to :program:`python -m json.tool`,
  which is :term:`soft deprecated`.
  See the :ref:`JSON command-line interface <json-commandline>` documentation.
  (Contributed by Trey Hunner in :gh:`122873`.)

* By default, the output of the :ref:`JSON command-line interface
  <json-commandline>` is highlighted in color.
  This can be controlled by :ref:`environment variables
  <using-on-controlling-color>`.
  (Contributed by Tomas Roun in :gh:`131952`.)


linecache
---------

* :func:`~linecache.getline` can now retrieve source code for frozen modules.
  (Contributed by Tian Gao in :gh:`131638`.)


logging.handlers
----------------

* :class:`~logging.handlers.QueueListener` objects now support the
  :term:`context manager` protocol.
  (Contributed by Charles Machalow in :gh:`132106`.)

* :meth:`QueueListener.start <logging.handlers.QueueListener.start>` now
  raises a :exc:`RuntimeError` if the listener is already started.
  (Contributed by Charles Machalow in :gh:`132106`.)


math
----

* Added more detailed error messages for domain errors in the module.
  (Contributed by Charlie Zhao and Sergey B Kirpichev in :gh:`101410`.)


mimetypes
---------

* Add a public :ref:`command-line <mimetypes-cli>` for the module,
  invoked via :program:`python -m mimetypes`.
  (Contributed by Oleg Iarygin and Hugo van Kemenade in :gh:`93096`.)

* Add several new MIME types based on RFCs and common usage:

  .. rubric:: Microsoft and :rfc:`8081` MIME types for fonts

  * Embedded OpenType: ``application/vnd.ms-fontobject``
  * OpenType Layout (OTF) ``font/otf``
  * TrueType: ``font/ttf``
  * WOFF 1.0 ``font/woff``
  * WOFF 2.0 ``font/woff2``

  .. rubric:: :rfc:`9559` MIME types for Matroska audiovisual
              data container structures

  * audio with no video: ``audio/matroska`` (``.mka``)
  * video: ``video/matroska`` (``.mkv``)
  * stereoscopic video: ``video/matroska-3d`` (``.mk3d``)

  .. rubric:: Images with RFCs

  * :rfc:`1494`: CCITT Group 3 (``.g3``)
  * :rfc:`3362`: Real-time Facsimile, T.38 (``.t38``)
  * :rfc:`3745`: JPEG 2000 (``.jp2``), extension (``.jpx``) and compound (``.jpm``)
  * :rfc:`3950`: Tag Image File Format Fax eXtended, TIFF-FX (``.tfx``)
  * :rfc:`4047`: Flexible Image Transport System (``.fits``)
  * :rfc:`7903`: Enhanced Metafile (``.emf``) and Windows Metafile (``.wmf``)

  .. rubric:: Other MIME type additions and changes

  * :rfc:`2361`: Change type for ``.avi`` to ``video/vnd.avi``
    and for ``.wav`` to ``audio/vnd.wave``
  * :rfc:`4337`: Add MPEG-4 ``audio/mp4`` (``.m4a``)
  * :rfc:`5334`: Add Ogg media (``.oga``, ``.ogg`` and ``.ogx``)
  * :rfc:`6713`: Add gzip ``application/gzip`` (``.gz``)
  * :rfc:`9639`: Add FLAC ``audio/flac`` (``.flac``)
  * :rfc:`9512` ``application/yaml`` MIME type for YAML files (``.yaml``
    and ``.yml``)
  * Add 7z ``application/x-7z-compressed`` (``.7z``)
  * Add Android Package ``application/vnd.android.package-archive`` (``.apk``)
    when not strict
  * Add deb ``application/x-debian-package`` (``.deb``)
  * Add glTF binary ``model/gltf-binary`` (``.glb``)
  * Add glTF JSON/ASCII ``model/gltf+json`` (``.gltf``)
  * Add M4V ``video/x-m4v`` (``.m4v``)
  * Add PHP ``application/x-httpd-php`` (``.php``)
  * Add RAR ``application/vnd.rar`` (``.rar``)
  * Add RPM ``application/x-rpm`` (``.rpm``)
  * Add STL ``model/stl`` (``.stl``)
  * Add Windows Media Video ``video/x-ms-wmv`` (``.wmv``)
  * De facto: Add WebM ``audio/webm`` (``.weba``)
  * `ECMA-376
    <https://ecma-international.org/publications-and-standards/standards/ecma-376/>`__:
    Add ``.docx``, ``.pptx`` and ``.xlsx`` types
  * `OASIS
    <https://docs.oasis-open.org/office/v1.2/cs01/OpenDocument-v1.2-cs01-part1.html#Appendix_C>`__:
    Add OpenDocument ``.odg``, ``.odp``, ``.ods`` and ``.odt`` types
  * `W3C <https://www.w3.org/TR/epub-33/#app-media-type>`__:
    Add EPUB ``application/epub+zip`` (``.epub``)

  (Contributed by Sahil Prajapati and Hugo van Kemenade in :gh:`84852`,
  by Sasha "Nelie" Chernykh and Hugo van Kemenade in :gh:`132056`,
  and by Hugo van Kemenade in :gh:`89416`, :gh:`85957`, and :gh:`129965`.)


multiprocessing
---------------

.. _whatsnew314-multiprocessing-start-method:

* On Unix platforms other than macOS, :ref:`'forkserver'
  <multiprocessing-start-method-forkserver>` is now the default :ref:`start
  method <multiprocessing-start-methods>`
  (replacing :ref:`'fork' <multiprocessing-start-method-fork>`).
  This change does not affect Windows or macOS, where :ref:`'spawn'
  <multiprocessing-start-method-spawn>` remains the default start method.

  If the threading incompatible *fork* method is required, you must explicitly
  request it via a context from :func:`~multiprocessing.get_context` (preferred)
  or change the default via :func:`~multiprocessing.set_start_method`.

  See :ref:`forkserver restrictions <multiprocessing-programming-forkserver>`
  for information and differences with the *fork* method and how this change
  may affect existing code with mutable global shared variables and/or shared
  objects that can not be automatically :mod:`pickled <pickle>`.

  (Contributed by Gregory P. Smith in :gh:`84559`.)

* :mod:`multiprocessing`'s ``'forkserver'`` start method now authenticates
  its control socket to avoid solely relying on filesystem permissions
  to restrict what other processes could cause the forkserver to spawn workers
  and run code.
  (Contributed by Gregory P. Smith for :gh:`97514`.)

* The :ref:`multiprocessing proxy objects <multiprocessing-proxy_objects>`
  for *list* and *dict* types gain previously overlooked missing methods:

   * :meth:`!clear` and :meth:`!copy` for proxies of :class:`list`
   * :meth:`~dict.fromkeys`, ``reversed(d)``, ``d | {}``, ``{} | d``,
     ``d |= {'b': 2}`` for proxies of :class:`dict`

  (Contributed by Roy Hyunjin Han for :gh:`103134`.)

* Add support for shared :class:`set` objects via
  :meth:`.SyncManager.set`.
  The :func:`set` in :func:`~multiprocessing.Manager` method is now available.
  (Contributed by Mingyu Park in :gh:`129949`.)

* Add the :meth:`~multiprocessing.Process.interrupt`
  to :class:`multiprocessing.Process` objects, which terminates the child
  process by sending :py:const:`~signal.SIGINT`. This enables
  :keyword:`finally` clauses to print a stack trace for the terminated
  process. (Contributed by Artem Pulkin in :gh:`131913`.)


operator
--------

* Add :func:`~operator.is_none` and :func:`~operator.is_not_none` as a pair
  of functions, 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
--

* Add the :func:`~os.reload_environ` function to update :data:`os.environ` and
  :data:`os.environb` 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`.)

* Add the :data:`~os.SCHED_DEADLINE` and :data:`~os.SCHED_NORMAL` constants
  to the :mod:`!os` module.
  (Contributed by James Roy in :gh:`127688`.)

* Add the :func:`~os.readinto` function to read into a
  :ref:`buffer object <bufferobjects>` from a file descriptor.
  (Contributed by Cody Maloney in :gh:`129205`.)


os.path
-------

* The *strict* parameter to :func:`~os.path.realpath` accepts a new value,
  :data:`~os.path.ALLOW_MISSING`.
  If used, errors other than :exc:`FileNotFoundError` will be re-raised;
  the resulting path can be missing but it will be free of symlinks.
  (Contributed by Petr Viktorin for :cve:`2025-4517`.)


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`.)

* Add the :attr:`~pathlib.Path.info` attribute, which stores an object
  implementing the new :class:`pathlib.types.PathInfo` protocol. The
  object supports querying the file type and internally caching
  :func:`~os.stat` results. Path objects generated by
  :meth:`~pathlib.Path.iterdir` are initialized with file type information
  gleaned from scanning the parent directory.
  (Contributed by Barney Gale in :gh:`125413`.)


pdb
---

* The :mod:`pdb` module now supports remote attaching to a running Python process
  using a new :option:`-p PID <pdb --pid>` command-line option:

  .. code-block:: sh

     python -m pdb -p 1234

  This will connect to the Python process with the given PID and allow you to
  debug it interactively. Notice that due to how the Python interpreter works
  attaching to a remote process that is blocked in a system call or waiting for
  I/O will only work once the next bytecode instruction is executed or when the
  process receives a signal.

  This feature uses :ref:`PEP 768 <whatsnew314-remote-debugging>`
  and the new :func:`sys.remote_exec` function to attach to the remote process
  and send the PDB commands to it.

  (Contributed by Matt Wozniski and Pablo Galindo in :gh:`131591`.)

* Hardcoded 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 hardcoded breakpoints.
  (Contributed by Tian Gao in :gh:`121450`.)

* Add a new argument *mode* to :class:`pdb.Pdb`. Disable the ``restart``
  command when :mod:`pdb` is in ``inline`` mode.
  (Contributed by Tian Gao in :gh:`123757`.)

* A confirmation prompt will be shown when the user tries to quit :mod:`pdb`
  in ``inline`` mode. ``y``, ``Y``, ``<Enter>`` or ``EOF`` will confirm
  the quit and call :func:`sys.exit`, instead of raising :exc:`bdb.BdbQuit`.
  (Contributed by Tian Gao in :gh:`124704`.)

* Inline breakpoints like :func:`breakpoint` or :func:`pdb.set_trace` will
  always stop the program at calling frame, ignoring the ``skip`` pattern
  (if any).
  (Contributed by Tian Gao in :gh:`130493`.)

* ``<tab>`` at the beginning of the line in :mod:`pdb` multi-line input will
  fill in a 4-space indentation now, instead of inserting a ``\t`` character.
  (Contributed by Tian Gao in :gh:`130471`.)

* Auto-indent is introduced in :mod:`pdb` multi-line input. It will either
  keep the indentation of the last line or insert a 4-space indentation when
  it detects a new code block.
  (Contributed by Tian Gao in :gh:`133350`.)

* ``$_asynctask`` is added to access the current asyncio task if applicable.
  (Contributed by Tian Gao in :gh:`124367`.)

* :func:`pdb.set_trace_async` is added to support debugging asyncio
  coroutines. :keyword:`await` statements are supported with this
  function.
  (Contributed by Tian Gao in :gh:`132576`.)

* Source code displayed in :mod:`pdb` will be syntax-highlighted. This feature
  can be controlled using the same methods as the default :term:`interactive`
  shell, in addition to the newly added ``colorize`` argument of :class:`pdb.Pdb`.
  (Contributed by Tian Gao and Łukasz Langa in :gh:`133355`.)


pickle
------

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

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


platform
--------

* Add :func:`~platform.invalidate_caches`, a function to invalidate
  cached results in the :mod:`!platform` module.
  (Contributed by Bénédikt Tran in :gh:`122549`.)


pydoc
-----

* :term:`Annotations <annotation>` in help output are now usually
  displayed in a format closer to that in the original source.
  (Contributed by Jelle Zijlstra in :gh:`101552`.)


re
--

* Support ``\z`` as a synonym for ``\Z`` in :mod:`regular expressions <re>`.
  It is interpreted unambiguously in many other regular expression engines,
  unlike ``\Z``, which has subtly different behavior.
  (Contributed by Serhiy Storchaka in :gh:`133306`.)

* ``\B`` in :mod:`regular expression <re>` now matches the empty input string,
  meaning that it is now always the opposite of ``\b``.
  (Contributed by Serhiy Storchaka in :gh:`124130`.)


socket
------

* Improve and fix support for Bluetooth sockets.

  * Fix support of Bluetooth sockets on NetBSD and DragonFly BSD.
    (Contributed by Serhiy Storchaka in :gh:`132429`.)
  * Fix support for :const:`~socket.BTPROTO_HCI` on FreeBSD.
    (Contributed by Victor Stinner in :gh:`111178`.)
  * Add support for :const:`~socket.BTPROTO_SCO` on FreeBSD.
    (Contributed by Serhiy Storchaka in :gh:`85302`.)
  * Add support for *cid* and *bdaddr_type* in the address for
    :const:`~socket.BTPROTO_L2CAP` on FreeBSD.
    (Contributed by Serhiy Storchaka in :gh:`132429`.)
  * Add support for *channel* in the address for
    :const:`~socket.BTPROTO_HCI` on Linux.
    (Contributed by Serhiy Storchaka in :gh:`70145`.)
  * Accept an integer as the address for
    :const:`~socket.BTPROTO_HCI` on Linux.
    (Contributed by Serhiy Storchaka in :gh:`132099`.)
  * Return *cid* in :meth:`~socket.socket.getsockname` for
    :const:`~socket.BTPROTO_L2CAP`.
    (Contributed by Serhiy Storchaka in :gh:`132429`.)
  * Add many new constants.
    (Contributed by Serhiy Storchaka in :gh:`132734`.)


ssl
---

* Indicate through the :data:`~ssl.HAS_PHA` Boolean whether the :mod:`!ssl`
  module supports TLSv1.3 post-handshake client authentication (PHA).
  (Contributed by Will Childs-Klein in :gh:`128036`.)


struct
------

* Support the :c:expr:`float complex` and :c:expr:`double complex` C types in
  the :mod:`struct` module (formatting characters ``'F'`` and ``'D'``
  respectively).
  (Contributed by Sergey B Kirpichev in :gh:`121249`.)


symtable
--------

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

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

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


sys
---

* The previously undocumented special function :func:`sys.getobjects`,
  which only exists in specialized builds of Python, may now return objects
  from other interpreters than the one it's called in.
  (Contributed by Eric Snow in :gh:`125286`.)

* Add :func:`sys._is_immortal` for determining if an object is :term:`immortal`.
  (Contributed by Peter Bierma in :gh:`128509`.)

* On FreeBSD, :data:`sys.platform` no longer contains the major version number.
  It is always ``'freebsd'``, instead of ``'freebsd13'`` or ``'freebsd14'``.
  (Contributed by Michael Osipov in :gh:`129393`.)

* Raise :exc:`DeprecationWarning` for :func:`sys._clear_type_cache`. This
  function was deprecated in Python 3.13 but it didn't raise a runtime warning.

* Add :func:`sys.remote_exec` to implement the new external debugger interface.
  See :ref:`PEP 768 <whatsnew314-remote-debugging>` for details.
  (Contributed by Pablo Galindo Salgado, Matt Wozniski, and Ivona Stojanovic
  in :gh:`131591`.)

* Add the :data:`sys._jit` namespace, containing utilities for introspecting
  just-in-time compilation.
  (Contributed by Brandt Bucher in :gh:`133231`.)


sys.monitoring
--------------

* Add two new monitoring events, :monitoring-event:`BRANCH_LEFT` and
  :monitoring-event:`BRANCH_RIGHT`.
  These replace and deprecate the :monitoring-event:`!BRANCH` event.
  (Contributed by Mark Shannon in :gh:`122548`.)


sysconfig
---------

* Add ``ABIFLAGS`` key to :func:`~sysconfig.get_config_vars` on Windows.
  (Contributed by Xuehai Pan in :gh:`131799`.)


tarfile
-------

* :func:`~tarfile.data_filter` now normalizes symbolic link targets in order to
  avoid path traversal attacks.
  (Contributed by Petr Viktorin in :gh:`127987` and :cve:`2025-4138`.)

* :func:`~tarfile.TarFile.extractall` now skips fixing up directory attributes
  when a directory was removed or replaced by another kind of file.
  (Contributed by Petr Viktorin in :gh:`127987` and :cve:`2024-12718`.)

* :func:`~tarfile.TarFile.extract` and :func:`~tarfile.TarFile.extractall`
  now (re-)apply the extraction filter when substituting a link (hard or
  symbolic) with a copy of another archive member, and when fixing up
  directory attributes.
  The former raises a new exception, :exc:`~tarfile.LinkFallbackError`.
  (Contributed by Petr Viktorin for :cve:`2025-4330` and :cve:`2024-12718`.)

* :func:`~tarfile.TarFile.extract` and :func:`~tarfile.TarFile.extractall`
  no longer extract rejected members when
  :func:`~tarfile.TarFile.errorlevel` is zero.
  (Contributed by Matt Prodani and Petr Viktorin in :gh:`112887`
  and :cve:`2025-4435`.)


threading
---------

* :meth:`threading.Thread.start` now sets the operating system thread name
  to :attr:`threading.Thread.name`.
  (Contributed by Victor Stinner in :gh:`59705`.)


tkinter
-------

* Make :mod:`tkinter` widget methods :meth:`!after` and :meth:`!after_idle`
  accept keyword arguments.
  (Contributed by Zhikang Yan in :gh:`126899`.)

* Add ability to specify a name for :class:`!tkinter.OptionMenu` and
  :class:`!tkinter.ttk.OptionMenu`.
  (Contributed by Zhikang Yan in :gh:`130482`.)


turtle
------

* Add context managers for :func:`turtle.fill`, :func:`turtle.poly`,
  and :func:`turtle.no_animation`.
  (Contributed by Marie Roald and Yngve Mardal Moe in :gh:`126350`.)


types
-----

* :class:`types.UnionType` is now an alias for :class:`typing.Union`.
  See :ref:`below <whatsnew314-typing-union>` for more details.
  (Contributed by Jelle Zijlstra in :gh:`105499`.)


typing
------

.. _whatsnew314-typing-union:

* The :class:`types.UnionType` and :class:`typing.Union` types are now
  aliases for each other, meaning that both old-style unions
  (created with ``Union[int, str]``) and new-style unions (``int | str``)
  now create instances of the same runtime type. This unifies the behavior
  between the two syntaxes, but leads to some differences in behavior that
  may affect users who introspect types at runtime:

  - Both syntaxes for creating a union now produce the same string
    representation in :func:`repr`.
    For example, ``repr(Union[int, str])`` is now ``"int | str"`` instead of
    ``"typing.Union[int, str]"``.

  - Unions created using the old syntax are no longer cached.
    Previously, running ``Union[int, str]`` multiple times would return
    the same object (``Union[int, str] is Union[int, str]`` would be ``True``),
    but now it will return two different objects.
    Use ``==`` to compare unions for equality, not ``is``.
    New-style unions have never been cached this way.
    This change could increase memory usage for some programs that use
    a large number of unions created by subscripting ``typing.Union``.
    However, several factors offset this cost:
    unions used in annotations are no longer evaluated by default in Python
    3.14 because of :pep:`649`; an instance of :class:`types.UnionType` is
    itself much smaller than the object returned by ``Union[]`` was on prior
    Python versions; and removing the cache also saves some space.
    It is therefore unlikely that this change will cause a significant increase
    in memory usage for most users.

  - Previously, old-style unions were implemented using the private class
    ``typing._UnionGenericAlias``.
    This class is no longer needed for the implementation,
    but it has been retained for backward compatibility,
    with removal scheduled for Python 3.17.
    Users should use documented introspection helpers like
    :func:`~typing.get_origin` and :func:`typing.get_args` instead of
    relying on private implementation details.

  - It is now possible to use :class:`typing.Union` itself in
    :func:`isinstance` checks.
    For example, ``isinstance(int | str, typing.Union)`` will return ``True``;
    previously this raised :exc:`TypeError`.

  - The :attr:`!__args__` attribute of :class:`typing.Union` objects is
    no longer writable.

  - It is no longer possible to set any attributes on :class:`~typing.Union`
    objects.
    This only ever worked for dunder attributes on previous versions, was never
    documented to work, and was subtly broken in many cases.

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

* :class:`~typing.TypeAliasType` now supports star unpacking.


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

* The Unicode database has been updated to Unicode 16.0.0.


unittest
--------

.. _whatsnew314-color-unittest:

* :mod:`unittest` output is now colored by default.
  This can be controlled by :ref:`environment variables
  <using-on-controlling-color>`.
  (Contributed by Hugo van Kemenade in :gh:`127221`.)

* unittest discovery supports :term:`namespace package` as start
  directory again. It was removed in Python 3.11.
  (Contributed by Jacob Walls in :gh:`80958`.)

* A number of new methods were added in the :class:`~unittest.TestCase` class
  that provide more specialized tests.

  - :meth:`~unittest.TestCase.assertHasAttr` and
    :meth:`~unittest.TestCase.assertNotHasAttr` check whether the object
    has a particular attribute.
  - :meth:`~unittest.TestCase.assertIsSubclass` and
    :meth:`~unittest.TestCase.assertNotIsSubclass` check whether the object
    is a subclass of a particular class, or of one of a tuple of classes.
  - :meth:`~unittest.TestCase.assertStartsWith`,
    :meth:`~unittest.TestCase.assertNotStartsWith`,
    :meth:`~unittest.TestCase.assertEndsWith` and
    :meth:`~unittest.TestCase.assertNotEndsWith` check whether the Unicode
    or byte string starts or ends with particular strings.

  (Contributed by Serhiy Storchaka in :gh:`71339`.)


urllib
------

* Upgrade HTTP digest authentication algorithm for :mod:`urllib.request` by
  supporting SHA-256 digest authentication as specified in :rfc:`7616`.
  (Contributed by Calvin Bui in :gh:`128193`.)

* Improve ergonomics and standards compliance when parsing and emitting
  ``file:`` URLs.

  In :func:`~urllib.request.url2pathname`:

  - Accept a complete URL when the new *require_scheme* argument is set to
    true.
  - Discard URL authority if it matches the local hostname.
  - Discard URL authority if it resolves to a local IP address when the new
    *resolve_host* argument is set to true.
  - Discard URL query and fragment components.
  - Raise :exc:`~urllib.error.URLError` if a URL authority isn't local,
    except on Windows where we return a UNC path as before.

  In :func:`~urllib.request.pathname2url`:

  - Return a complete URL when the new *add_scheme* argument is set to true.
  - Include an empty URL authority when a path begins with a slash. For
    example, the path ``/etc/hosts`` is converted to the URL ``///etc/hosts``.

  On Windows, drive letters are no longer converted to uppercase, and ``:``
  characters not following a drive letter no longer cause an :exc:`OSError`
  exception to be raised.

  (Contributed by Barney Gale in :gh:`125866`.)


uuid
----

* Add support for UUID versions 6, 7, and 8 via :func:`~uuid.uuid6`,
  :func:`~uuid.uuid7`, and :func:`~uuid.uuid8` respectively, as specified
  in :rfc:`9562`.
  (Contributed by Bénédikt Tran in :gh:`89083`.)

* :const:`~uuid.NIL` and :const:`~uuid.MAX` are now available to represent the
  Nil and Max UUID formats as defined by :rfc:`9562`.
  (Contributed by Nick Pope in :gh:`128427`.)

* Allow generating multiple UUIDs simultaneously on the command-line via
  :option:`python -m uuid --count <uuid --count>`.
  (Contributed by Simon Legner in :gh:`131236`.)


webbrowser
----------

* Names in the :envvar:`BROWSER` environment variable can now refer to already
  registered browsers for the :mod:`webbrowser` module, instead of always
  generating a new browser command.

  This makes it possible to set :envvar:`BROWSER` to the value of one of the
  supported browsers on macOS.


zipfile
-------

* Added :meth:`ZipInfo._for_archive <zipfile.ZipInfo._for_archive>`, a method
  to resolve suitable defaults for a :class:`~zipfile.ZipInfo` object
  as used by :func:`ZipFile.writestr <zipfile.ZipFile.writestr>`.
  (Contributed by Bénédikt Tran in :gh:`123424`.)

* :meth:`.ZipFile.writestr` now respects the :envvar:`SOURCE_DATE_EPOCH`
  environment variable in order to better support reproducible builds.
  (Contributed by Jiahao Li in :gh:`91279`.)


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


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

* The import time for several standard library modules has been improved,
  including :mod:`annotationlib`, :mod:`ast`, :mod:`asyncio`, :mod:`base64`,
  :mod:`cmd`, :mod:`csv`, :mod:`gettext`, :mod:`importlib.util`, :mod:`locale`,
  :mod:`mimetypes`, :mod:`optparse`, :mod:`pickle`, :mod:`pprint`,
  :mod:`pstats`, :mod:`shlex`, :mod:`socket`, :mod:`string`, :mod:`subprocess`,
  :mod:`threading`, :mod:`tomllib`, :mod:`types`, and :mod:`zipfile`.

  (Contributed by Adam Turner, Bénédikt Tran, Chris Markiewicz, Eli Schwartz,
  Hugo van Kemenade, Jelle Zijlstra, and others in :gh:`118761`.)

* The interpreter now avoids some reference count modifications internally
  when it's safe to do so.
  This can lead to different values being returned from :func:`sys.getrefcount`
  and :c:func:`Py_REFCNT` compared to previous versions of Python.
  See :ref:`below <whatsnew314-refcount>` for details.


asyncio
-------

* Standard benchmark results have improved by 10-20% following the
  implementation of a new per-thread doubly linked list
  for :class:`native tasks <asyncio.Task>`,
  also reducing memory usage.
  This enables external introspection tools such as
  :ref:`python -m asyncio pstree <whatsnew314-asyncio-introspection>`
  to introspect the call graph of asyncio tasks running in all threads.
  (Contributed by Kumar Aditya in :gh:`107803`.)

* The module now has first class support for
  :term:`free-threading builds <free threading>`.
  This enables parallel execution of multiple event loops across
  different threads, scaling linearly with the number of threads.
  (Contributed by Kumar Aditya in :gh:`128002`.)


base64
------

* :func:`~base64.b16decode` is now up to six times faster.
  (Contributed by Bénédikt Tran, Chris Markiewicz, and Adam Turner
  in :gh:`118761`.)


bdb
---

* The basic debugger now has a :mod:`sys.monitoring`-based backend,
  which can be selected via the passing ``'monitoring'``
  to the :class:`~bdb.Bdb` class's new *backend* parameter.
  (Contributed by Tian Gao in :gh:`124533`.)


difflib
-------

* The :func:`~difflib.IS_LINE_JUNK` function is now up to twice as fast.
  (Contributed by Adam Turner and Semyon Moroz in :gh:`130167`.)


gc
--

* The new :ref:`incremental garbage collector <whatsnew314-incremental-gc>`
  means that maximum pause times are reduced
  by an order of magnitude or more for larger heaps.

  Because of this optimization, the meaning of the results of
  :meth:`~gc.get_threshold` and :meth:`~gc.set_threshold` have changed,
  along with :meth:`~gc.get_count` and :meth:`~gc.get_stats`.

  - For backwards compatibility, :meth:`~gc.get_threshold` continues to return
    a three-item tuple.
    The first value is the threshold for young collections, as before;
    the second value determines the rate at which the old collection is scanned
    (the default is 10, and higher values mean that the old collection
    is scanned more slowly).
    The third value is now meaningless and is always zero.

  - :meth:`~gc.set_threshold` now ignores any items after the second.

  - :meth:`~gc.get_count` and :meth:`~gc.get_stats` continue to return
    the same format of results.
    The only difference is that instead of the results referring to
    the young, aging and old generations,
    the results refer to the young generation
    and the aging and collecting spaces of the old generation.

  In summary, code that attempted to manipulate the behavior of the cycle GC
  may not work exactly as intended, but it is very unlikely to be harmful.
  All other code will work just fine.

  (Contributed by Mark Shannon in :gh:`108362`.)


io
---

* Opening and reading files now executes fewer system calls.
  Reading a small operating system cached file in full is up to 15% faster.
  (Contributed by Cody Maloney and Victor Stinner
  in :gh:`120754` and :gh:`90102`.)


pathlib
-------

* :func:`Path.read_bytes <pathlib.Path.read_bytes>` now uses unbuffered mode
  to open files, which is between 9% and 17% faster to read in full.
  (Contributed by Cody Maloney in :gh:`120754`.)


pdb
---

* :mod:`pdb` now supports two backends, based on either
  :func:`sys.settrace` or :mod:`sys.monitoring`.
  Using the :ref:`pdb CLI <pdb-cli>` or :func:`breakpoint`
  will always use the :mod:`sys.monitoring` backend.
  Explicitly instantiating :class:`pdb.Pdb` and its derived classes
  will use the :func:`sys.settrace` backend by default, which is configurable.
  (Contributed by Tian Gao in :gh:`124533`.)


uuid
----

* :func:`~uuid.uuid3` and :func:`~uuid.uuid5` are now both roughly 40% faster
  for 16-byte names and 20% faster for 1024-byte names.
  Performance for longer names remains unchanged.
  (Contributed by Bénédikt Tran in :gh:`128150`.)

* :func:`~uuid.uuid4` is now c. 30% faster.
  (Contributed by Bénédikt Tran in :gh:`128150`.)


zlib
----

* On Windows, `zlib-ng <https://github.com/zlib-ng/zlib-ng>`__
  is now used as the implementation of the :mod:`zlib` module
  in the default binaries.
  There are no known incompatibilities between ``zlib-ng``
  and the previously-used ``zlib`` implementation.
  This should result in better performance at all compression levels.

  It is worth noting that ``zlib.Z_BEST_SPEED`` (``1``) may result in
  significantly less compression than the previous implementation,
  whilst also significantly reducing the time taken to compress.

  (Contributed by Steve Dower in :gh:`91349`.)


Removed
=======

argparse
--------

* Remove the *type*, *choices*, and *metavar* parameters
  of :class:`!BooleanOptionalAction`.
  These have been deprecated since Python 3.12.
  (Contributed by Nikita Sobolev in :gh:`118805`.)

* Calling :meth:`~argparse.ArgumentParser.add_argument_group`
  on an argument group now raises a :exc:`ValueError`.
  Similarly, :meth:`~argparse.ArgumentParser.add_argument_group`
  or :meth:`~argparse.ArgumentParser.add_mutually_exclusive_group`
  on a mutually exclusive group now both raise :exc:`ValueError`\ s.
  This 'nesting' was never supported, often failed to work correctly,
  and was unintentionally exposed through inheritance.
  This functionality has been deprecated since Python 3.11.
  (Contributed by Savannah Ostrowski in :gh:`127186`.)


ast
---

* Remove the following classes, which have been deprecated aliases of
  :class:`~ast.Constant` since Python 3.8 and have emitted
  deprecation warnings since Python 3.12:

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

  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 :class:`!NodeVisitor` subclass is visiting an AST.
  Define a ``visit_Constant`` method instead.

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

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

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

  Use :attr:`!Constant.value` instead.
  (Contributed by Alex Waygood in :gh:`119562`.)


asyncio
-------

* Remove the following classes, methods, and functions,
  which have been deprecated since Python 3.12:

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

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

* :func:`asyncio.get_event_loop` now raises a :exc:`RuntimeError`
  if there is no current event loop,
  and no longer implicitly creates an event loop.

  (Contributed by Kumar Aditya in :gh:`126353`.)

  .. TODO: move these patterns to the asyncio docs?
           quite long for What's New

  There's a few patterns that use :func:`asyncio.get_event_loop`, most
  of them can be replaced with :func:`asyncio.run`.

  If you're running an async function, simply use :func:`asyncio.run`.

  Before:

  .. code:: python

     async def main():
         ...


     loop = asyncio.get_event_loop()
     try:
         loop.run_until_complete(main())
     finally:
         loop.close()

  After:

  .. code:: python

    async def main():
        ...

    asyncio.run(main())

  If you need to start something, for example, a server listening on a socket
  and then run forever, use :func:`asyncio.run` and an
  :class:`asyncio.Event`.

  Before:

  .. code:: python

     def start_server(loop): ...

     loop = asyncio.get_event_loop()
     try:
         start_server(loop)
         loop.run_forever()
     finally:
         loop.close()

  After:

  .. code:: python

     def start_server(loop): ...

     async def main():
         start_server(asyncio.get_running_loop())
         await asyncio.Event().wait()

     asyncio.run(main())

  If you need to run something in an event loop, then run some blocking
  code around it, use :class:`asyncio.Runner`.

  Before:

  .. code:: python

     async def operation_one(): ...
     def blocking_code(): ...
     async def operation_two(): ...

     loop = asyncio.get_event_loop()
     try:
         loop.run_until_complete(operation_one())
         blocking_code()
         loop.run_until_complete(operation_two())
     finally:
         loop.close()

  After:

  .. code:: python

     async def operation_one(): ...
     def blocking_code(): ...
     async def operation_two(): ...

     with asyncio.Runner() as runner:
         runner.run(operation_one())
         blocking_code()
         runner.run(operation_two())


email
-----

* Remove :func:`email.utils.localtime`'s *isdst* parameter,
  which was deprecated in and has been ignored since Python 3.12.
  (Contributed by Hugo van Kemenade in :gh:`118798`.)


importlib.abc
-------------

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

  * :class:`!ResourceReader`
    (use :class:`~importlib.resources.abc.TraversableResources`)
  * :class:`!Traversable`
    (use :class:`~importlib.resources.abc.Traversable`)
  * :class:`!TraversableResources`
    (use :class:`~importlib.resources.abc.TraversableResources`)

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


itertools
---------

* Remove support for copy, deepcopy, and pickle operations
  from :mod:`itertools` iterators.
  These have emitted 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.
  (Contributed by Barney Gale in :gh:`74033`.)

* Remove support for passing additional positional arguments to
  :meth:`.PurePath.relative_to` and :meth:`~pathlib.PurePath.is_relative_to`.
  In previous versions, any such arguments are joined onto *other*.
  (Contributed by Barney Gale in :gh:`78707`.)


pkgutil
-------

* Remove the :func:`!get_loader` and :func:`!find_loader` functions,
  which have been deprecated since Python 3.12.
  (Contributed by Bénédikt Tran in :gh:`97850`.)


pty
---

* Remove the :func:`!master_open` and :func:`!slave_open` functions,
  which have been deprecated 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
  the :mod:`sqlite3` module;
  use :data:`~sqlite3.sqlite_version` and :data:`~sqlite3.sqlite_version_info`
  for the actual version number of the runtime SQLite library.
  (Contributed by Hugo van Kemenade in :gh:`118924`.)

* Using a sequence of parameters with named placeholders now
  raises a :exc:`~sqlite3.ProgrammingError`,
  having been deprecated since Python 3.12.
  (Contributed by Erlend E. Aasland in :gh:`118928` and :gh:`101693`.)


urllib
------

* Remove the :class:`!Quoter` class from :mod:`urllib.parse`,
  which has been deprecated since Python 3.11.
  (Contributed by Nikita Sobolev in :gh:`118827`.)

* Remove the :class:`!URLopener` and :class:`!FancyURLopener` classes
  from :mod:`urllib.request`,
  which have been deprecated since Python 3.3.

  ``myopener.open()`` can be replaced with :func:`~urllib.request.urlopen`.
  ``myopener.retrieve()`` can be replaced with
  :func:`~urllib.request.urlretrieve`.
  Customisations to the opener classes can be replaced by passing
  customized handlers to :func:`~urllib.request.build_opener`.
  (Contributed by Barney Gale in :gh:`84850`.)


Deprecated
==========

New deprecations
----------------

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

* :mod:`argparse`:

  * Passing the undocumented keyword argument *prefix_chars* to the
    :meth:`~argparse.ArgumentParser.add_argument_group` method is now deprecated.
    (Contributed by Savannah Ostrowski in :gh:`125563`.)

  * Deprecated the :class:`argparse.FileType` type converter.
    Anything relating to resource management should be handled
    downstream, after the arguments have been parsed.
    (Contributed by Serhiy Storchaka in :gh:`58032`.)

* :mod:`asyncio`:

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

  * The :mod:`asyncio` policy system is deprecated
    and will be removed in Python 3.16.
    In particular, the following classes and functions are deprecated:

    * :class:`asyncio.AbstractEventLoopPolicy`
    * :class:`asyncio.DefaultEventLoopPolicy`
    * :class:`asyncio.WindowsSelectorEventLoopPolicy`
    * :class:`asyncio.WindowsProactorEventLoopPolicy`
    * :func:`asyncio.get_event_loop_policy`
    * :func:`asyncio.set_event_loop_policy`

    Users should use :func:`asyncio.run` or :class:`asyncio.Runner` with
    the *loop_factory* argument to use the desired event loop implementation.

    For example, to use :class:`asyncio.SelectorEventLoop` on Windows:

    .. code-block:: python

       import asyncio

       async def main():
           ...

       asyncio.run(main(), loop_factory=asyncio.SelectorEventLoop)

    (Contributed by Kumar Aditya in :gh:`127949`.)

* :mod:`codecs`:
  The :func:`codecs.open` function is now deprecated,
  and will be removed in a future version of Python.
  Use :func:`open` instead.
  (Contributed by Inada Naoki in :gh:`133036`.)

* :mod:`ctypes`:

  * On non-Windows platforms, setting :attr:`.Structure._pack_` to use a
    MSVC-compatible default memory layout is now deprecated in favor of setting
    :attr:`.Structure._layout_` to ``'ms'``, and will be removed in Python 3.19.
    (Contributed by Petr Viktorin in :gh:`131747`.)

  * Calling :func:`ctypes.POINTER` on a string is now deprecated.
    Use :ref:`incomplete types <ctypes-incomplete-types>`
    for self-referential structures.
    Also, the internal ``ctypes._pointer_type_cache`` is deprecated.
    See :func:`ctypes.POINTER` for updated implementation details.
    (Contributed by Sergey Myrianov in :gh:`100926`.)

* :mod:`functools`:
  Calling the Python implementation of :func:`functools.reduce` with *function*
  or *sequence* as keyword arguments is now deprecated;
  the parameters will be made positional-only in Python 3.16.
  (Contributed by Kirill Podoprigora in :gh:`121676`.)

* :mod:`logging`:
  Support for custom logging handlers with the *strm* argument
  is now deprecated and scheduled for removal in Python 3.16.
  Define handlers with the *stream* argument instead.
  (Contributed by Mariusz Felisiak in :gh:`115032`.)

* :mod:`mimetypes`:
  Valid extensions are either empty or must start with '.' for
  :meth:`mimetypes.MimeTypes.add_type`.
  Undotted extensions are deprecated and will
  raise a :exc:`ValueError` in Python 3.16.
  (Contributed by Hugo van Kemenade in :gh:`75223`.)

* :mod:`!nturl2path`:
  This module is now deprecated. Call :func:`urllib.request.url2pathname`
  and :func:`~urllib.request.pathname2url` instead.
  (Contributed by Barney Gale in :gh:`125866`.)

* :mod:`os`:
  The :func:`os.popen` and :func:`os.spawn* <os.spawnl>` functions
  are now :term:`soft deprecated`.
  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:`pathlib`:
  :meth:`!pathlib.PurePath.as_uri` is now deprecated
  and scheduled for removal in Python 3.19.
  Use :meth:`pathlib.Path.as_uri` instead.
  (Contributed by Barney Gale in :gh:`123599`.)

* :mod:`pdb`:
  The undocumented ``pdb.Pdb.curframe_locals`` attribute is now a deprecated
  read-only property, which will be removed in a future version of Python.
  The low overhead dynamic frame locals access added in Python 3.13 by :pep:`667`
  means the frame locals cache reference previously stored in this attribute
  is no longer needed. Derived debuggers should access
  ``pdb.Pdb.curframe.f_locals`` directly in Python 3.13 and later versions.
  (Contributed by Tian Gao in :gh:`124369` and :gh:`125951`.)

* :mod:`symtable`:
  Deprecate :meth:`symtable.Class.get_methods` due to the lack of interest,
  scheduled for removal in Python 3.16.
  (Contributed by Bénédikt Tran in :gh:`119698`.)

* :mod:`tkinter`:
  The :class:`!tkinter.Variable` methods :meth:`!trace_variable`,
  :meth:`!trace_vdelete` and :meth:`!trace_vinfo` are now deprecated.
  Use :meth:`!trace_add`, :meth:`!trace_remove` and :meth:`!trace_info` instead.
  (Contributed by Serhiy Storchaka in :gh:`120220`.)

* :mod:`urllib.parse`:
  Accepting objects with false values (like ``0`` and ``[]``) except empty
  strings, bytes-like objects and ``None`` in :func:`~urllib.parse.parse_qsl`
  and :func:`~urllib.parse.parse_qs` is now deprecated.
  (Contributed by Serhiy Storchaka in :gh:`116897`.)

.. 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-3.17.rst

.. include:: ../deprecations/pending-removal-in-3.19.rst

.. include:: ../deprecations/pending-removal-in-3.20.rst

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


CPython bytecode changes
========================

* Replaced the opcode :opcode:`!BINARY_SUBSCR` by the :opcode:`BINARY_OP`
  opcode with the ``NB_SUBSCR`` oparg.
  (Contributed by Irit Katriel in :gh:`100239`.)

* Add the :opcode:`BUILD_INTERPOLATION` and :opcode:`BUILD_TEMPLATE`
  opcodes to construct new :class:`~string.templatelib.Interpolation`
  and :class:`~string.templatelib.Template` instances, respectively.
  (Contributed by Lysandros Nikolaou and others in :gh:`132661`;
  see also :ref:`PEP 750: Template strings <whatsnew314-template-string-literals>`).

* Remove the :opcode:`!BUILD_CONST_KEY_MAP` opcode.
  Use :opcode:`BUILD_MAP` instead.
  (Contributed by Mark Shannon in :gh:`122160`.)

* Replace the :opcode:`!LOAD_ASSERTION_ERROR` opcode with
  :opcode:`LOAD_COMMON_CONSTANT` and add support for loading
  :exc:`NotImplementedError`.

* Add the :opcode:`LOAD_FAST_BORROW` and :opcode:`LOAD_FAST_BORROW_LOAD_FAST_BORROW`
  opcodes to reduce reference counting overhead when the interpreter can prove
  that the reference in the frame outlives the reference loaded onto the stack.
  (Contributed by Matt Page in :gh:`130704`.)

* Add the :opcode:`LOAD_SMALL_INT` opcode, which pushes a small integer
  equal to the ``oparg`` to the stack.
  The :opcode:`!RETURN_CONST` opcode is removed as it is no longer used.
  (Contributed by Mark Shannon in :gh:`125837`.)

* Add the new :opcode:`LOAD_SPECIAL` instruction.
  Generate code for :keyword:`with` and :keyword:`async with` statements
  using the new instruction.
  Removed the :opcode:`!BEFORE_WITH` and :opcode:`!BEFORE_ASYNC_WITH` instructions.
  (Contributed by Mark Shannon in :gh:`120507`.)

* Add the :opcode:`POP_ITER` opcode to support 'virtual' iterators.
  (Contributed by Mark Shannon in :gh:`132554`.)


Pseudo-instructions
-------------------

* Add the :opcode:`!ANNOTATIONS_PLACEHOLDER` pseudo instruction
  to support partially executed module-level annotations with
  :ref:`deferred evaluation of annotations <whatsnew314-deferred-annotations>`.
  (Contributed by Jelle Zijlstra in :gh:`130907`.)

* Add the :opcode:`!BINARY_OP_EXTEND` pseudo instruction,
  which executes a pair of functions (guard and specialization functions)
  accessed from the inline cache.
  (Contributed by Irit Katriel in :gh:`100239`.)

* Add three specializations for :opcode:`CALL_KW`;
  :opcode:`!CALL_KW_PY` for calls to Python functions,
  :opcode:`!CALL_KW_BOUND_METHOD` for calls to bound methods, and
  :opcode:`!CALL_KW_NON_PY` for all other calls.
  (Contributed by Mark Shannon in :gh:`118093`.)

* Add the :opcode:`JUMP_IF_TRUE` and :opcode:`JUMP_IF_FALSE` pseudo instructions,
  conditional jumps which do not impact the stack.
  Replaced by the sequence ``COPY 1``, ``TO_BOOL``, ``POP_JUMP_IF_TRUE/FALSE``.
  (Contributed by Irit Katriel in :gh:`124285`.)

* Add the :opcode:`!LOAD_CONST_MORTAL` pseudo instruction.
  (Contributed by Mark Shannon in :gh:`128685`.)

* Add the :opcode:`!LOAD_CONST_IMMORTAL` pseudo instruction,
  which does the same as :opcode:`!LOAD_CONST`, but is more efficient
  for immortal objects.
  (Contributed by Mark Shannon in :gh:`125837`.)

* Add the :opcode:`NOT_TAKEN` pseudo instruction, used by :mod:`sys.monitoring`
  to record branch events (such as :monitoring-event:`BRANCH_LEFT`).
  (Contributed by Mark Shannon in :gh:`122548`.)


C API changes
=============

.. _whatsnew314-capi-config:

Python configuration C API
--------------------------

Add a :ref:`PyInitConfig C API <pyinitconfig_api>` to configure the Python
initialization without relying on C structures and the ability to make
ABI-compatible changes in the future.

Complete the :pep:`587` :ref:`PyConfig C API <pyconfig_api>` by adding
:c:func:`PyInitConfig_AddModule` which can be used to add a built-in extension
module; a feature previously referred to as the "inittab".

Add :c:func:`PyConfig_Get` and :c:func:`PyConfig_Set` functions to get and set
the current runtime configuration.

:pep:`587` 'Python Initialization Configuration' unified all the ways
to configure Python's initialization. This PEP also unifies the configuration
of Python's preinitialization and initialization in a single API.
Moreover, this PEP only provides a single choice to embed Python,
instead of having two 'Python' and 'Isolated' choices (PEP 587),
to further simplify the API.

The lower level PEP 587 PyConfig API remains available for use cases
with an intentionally higher level of coupling to CPython implementation details
(such as emulating the full functionality of CPython's CLI, including its
configuration mechanisms).

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

.. seealso:: :pep:`741` and :pep:`587`


New features in the C API
-------------------------

* Add :c:func:`Py_PACK_VERSION` and :c:func:`Py_PACK_FULL_VERSION`,
  two new macros for bit-packing Python version numbers.
  This is useful for comparisons with :c:var:`Py_Version`
  or :c:macro:`PY_VERSION_HEX`.
  (Contributed by Petr Viktorin in :gh:`128629`.)

* 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 functions to manipulate the configuration of the current
  runtime Python interpreter
  (:ref:`PEP 741: Python configuration C API <whatsnew314-capi-config>`):

  * :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 Python initialization
  (:ref:`PEP 741: Python configuration C API <whatsnew314-capi-config>`):

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

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

* Add :c:func:`Py_fopen` function to open a file.
  This works similarly to the standard C :c:func:`!fopen` function,
  instead accepting a Python object for the *path* parameter
  and setting an exception on error.
  The corresponding new :c:func:`Py_fclose` function should be used
  to close a file.
  (Contributed by Victor Stinner in :gh:`127350`.)

* 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 :c:func:`PyImport_ImportModuleAttr` and
  :c:func:`PyImport_ImportModuleAttrString` helper functions to import a module
  and get an attribute of the module.
  (Contributed by Victor Stinner in :gh:`128911`.)

* 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`.)

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

* Add :c:func:`PyLong_IsPositive`, :c:func:`PyLong_IsNegative`
  and :c:func:`PyLong_IsZero` for checking if :c:type:`PyLongObject`
  is positive, negative, or zero, respectively.
  (Contributed by James Roy and Sergey B Kirpichev in :gh:`126061`.)

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

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

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

* Add a new import and export API for Python :class:`int` objects
  (:pep:`757`):

  * :c:func:`PyLong_GetNativeLayout`
  * :c:func:`PyLong_Export`
  * :c:func:`PyLong_FreeExport`
  * :c:func:`PyLongWriter_Create`
  * :c:func:`PyLongWriter_Finish`
  * :c:func:`PyLongWriter_Discard`

  (Contributed by Sergey B Kirpichev and Victor Stinner in :gh:`102471`.)

* Add :c:func:`PyMonitoring_FireBranchLeftEvent` and
  :c:func:`PyMonitoring_FireBranchRightEvent` for generating
  :monitoring-event:`BRANCH_LEFT` and :monitoring-event:`BRANCH_RIGHT`
  events, respectively.
  (Contributed by Mark Shannon in :gh:`122548`.)

* Add :c:func:`PyType_Freeze` function to make a type immutable.
  (Contributed by Victor Stinner in :gh:`121654`.)

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

* Add a new :c:func:`PyUnicode_Equal` function to test if two
  strings are equal.
  The function is also added to the Limited C API.
  (Contributed by Victor Stinner in :gh:`124502`.)

* Add a new :c:type:`PyUnicodeWriter` API to create a Python :class:`str`
  object, with the following functions:

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

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

* The ``k`` and ``K`` formats in :c:func:`PyArg_ParseTuple` and
  similar functions now use :meth:`~object.__index__` if available,
  like all other integer formats.
  (Contributed by Serhiy Storchaka in :gh:`112068`.)

* Add support for a new ``p`` format unit in :c:func:`Py_BuildValue`
  that produces a Python :class:`bool` object from a C integer.
  (Contributed by Pablo Galindo in :issue:`45325`.)

* Add :c:func:`PyUnstable_IsImmortal` for determining if
  an object is :term:`immortal`, for debugging purposes.
  (Contributed by Peter Bierma in :gh:`128509`.)

* Add :c:func:`PyUnstable_Object_EnableDeferredRefcount` for enabling
  deferred reference counting, as outlined in :pep:`703`.

* Add :c:func:`PyUnstable_Object_IsUniquelyReferenced` as
  a replacement for ``Py_REFCNT(op) == 1`` on :term:`free threaded
  <free threading>` builds.
  (Contributed by Peter Bierma in :gh:`133140`.)

* Add :c:func:`PyUnstable_Object_IsUniqueReferencedTemporary` to
  determine if an object is a unique temporary object on the
  interpreter's operand stack.
  This can be used in some cases as a replacement for checking
  if :c:func:`Py_REFCNT` is ``1`` for Python objects passed
  as arguments to C API functions.
  (Contributed by Sam Gross in :gh:`133164`.)


Limited C API changes
---------------------

* In the limited C API version 3.14 and newer, :c:func:`Py_TYPE` and
  :c:func:`Py_REFCNT` are now implemented as an opaque function call
  to hide implementation details.
  (Contributed by Victor Stinner in :gh:`120600` and :gh:`124127`.)

* Remove the :c:macro:`PySequence_Fast_GET_SIZE`,
  :c:macro:`PySequence_Fast_GET_ITEM`,
  and :c:macro:`PySequence_Fast_ITEMS`
  macros from the limited C API, since they have always been broken
  in the limited C API.
  (Contributed by Victor Stinner in :gh:`91417`.)


.. _whatsnew314-c-api-removed:

Removed C APIs
--------------

* Creating :c:data:`immutable types <Py_TPFLAGS_IMMUTABLETYPE>` with
  mutable bases was deprecated in Python 3.12,
  and now raises a :exc:`TypeError`.
  (Contributed by Nikita Sobolev in :gh:`119775`.)

* Remove ``PyDictObject.ma_version_tag`` member, which was deprecated
  in Python 3.12.
  Use the :c:func:`PyDict_AddWatcher` API instead.
  (Contributed by Sam Gross in :gh:`124296`.)

* Remove the private ``_Py_InitializeMain()`` function.
  It was a :term:`provisional API` added to Python 3.8 by :pep:`587`.
  (Contributed by Victor Stinner in :gh:`129033`.)

* Remove the undocumented APIs :c:macro:`!Py_C_RECURSION_LIMIT`
  and :c:member:`!PyThreadState.c_recursion_remaining`.
  These were added in 3.13 and have been removed without deprecation.
  Use :c:func:`Py_EnterRecursiveCall` to guard against runaway
  recursion in C code.
  (Removed by Petr Viktorin in :gh:`133079`, see also :gh:`130396`.)


.. _whatsnew314-c-api-deprecated:

Deprecated C APIs
-----------------

* The :c:macro:`!Py_HUGE_VAL` macro is now :term:`soft deprecated`.
  Use :c:macro:`!INFINITY` instead.
  (Contributed by Sergey B Kirpichev in :gh:`120026`.)

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

* Non-tuple sequences are now deprecated as argument for the ``(items)``
  format unit in :c:func:`PyArg_ParseTuple` and other :ref:`argument
  parsing <arg-parsing>` functions if *items* contains format units
  which store a :ref:`borrowed buffer <c-arg-borrowed-buffer>` or a
  :term:`borrowed reference`.
  (Contributed by Serhiy Storchaka in :gh:`50333`.)

* The ``_PyMonitoring_FireBranchEvent`` function is now deprecated
  and should be replaced with calls to
  :c:func:`PyMonitoring_FireBranchLeftEvent` and
  :c:func:`PyMonitoring_FireBranchRightEvent`.

* The previously undocumented function :c:func:`PySequence_In` is
  now :term:`soft deprecated`.
  Use :c:func:`PySequence_Contains` instead.
  (Contributed by Yuki Kobayashi in :gh:`127896`.)

.. Add C API 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-3.16.rst

.. include:: ../deprecations/c-api-pending-removal-in-3.18.rst

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


.. _whatsnew314-build-changes:

Build changes
=============

* :pep:`776`: Emscripten is now an officially supported platform at
  :pep:`tier 3 <11#tier-3>`. As a part of this effort, more than 25 bugs in
  `Emscripten libc`__ were fixed. Emscripten now includes support
  for :mod:`ctypes`, :mod:`termios`, and :mod:`fcntl`, as well as
  experimental support for the new :ref:`default interactive shell
  <tut-interactive>`.
  (Contributed by R. Hood Chatham in :gh:`127146`, :gh:`127683`, and :gh:`136931`.)

  __ https://emscripten.org/docs/porting/emscripten-runtime-environment.html

* Official Android binary releases are now provided on python.org__.

  __ https://www.python.org/downloads/android/

* GNU Autoconf 2.72 is now required to generate :file:`configure`.
  (Contributed by Erlend Aasland in :gh:`115765`.)

* ``wasm32-unknown-emscripten`` is now a :pep:`11` tier 3 platform.
  (Contributed by R. Hood Chatham in :gh:`127146`, :gh:`127683`, and :gh:`136931`.)

* ``#pragma``-based linking with ``python3*.lib`` can now be switched off
  with :c:expr:`Py_NO_LINK_LIB`.
  (Contributed by Jean-Christophe Fillion-Robin in :gh:`82909`.)

* CPython now enables a set of recommended compiler options by default
  for improved security.
  Use the :option:`--disable-safety` :file:`configure` option to disable them,
  or the :option:`--enable-slower-safety` option for a larger set
  of compiler options, albeit with a performance cost.

* The ``WITH_FREELISTS`` macro and ``--without-freelists`` :file:`configure`
  option have been removed.

* The new :file:`configure` option :option:`--with-tail-call-interp`
  may be used to enable the experimental tail call interpreter.
  See :ref:`whatsnew314-tail-call-interpreter` for further details.

* To disable the new remote debugging support, use the
  :option:`--without-remote-debug` :file:`configure` option.
  This may be useful for security reasons.

* iOS and macOS apps can now be configured to redirect ``stdout`` and
  ``stderr`` content to the system log.
  (Contributed by Russell Keith-Magee in :gh:`127592`.)

* The iOS testbed is now able to stream test output while the test is running.
  The testbed can also be used to run the test suite of projects other than
  CPython itself.
  (Contributed by Russell Keith-Magee in :gh:`127592`.)


.. _whatsnew314-build_details:

:file:`build-details.json`
--------------------------

Installations of Python now contain a new file, :file:`build-details.json`.
This is a static JSON document containing build details for CPython,
to allow for introspection without needing to run code.
This is helpful for use-cases such as Python launchers, cross-compilation,
and so on.

:file:`build-details.json` must be installed in the platform-independent
standard library directory. This corresponds to the :ref:`'stdlib'
<installation_paths>` :mod:`sysconfig` installation path,
which can be found by running ``sysconfig.get_path('stdlib')``.

.. seealso::
   :pep:`739` -- ``build-details.json`` 1.0 -- a static description file
   for Python build details


.. _whatsnew314-no-more-pgp:

Discontinuation of PGP signatures
---------------------------------

PGP (Pretty Good Privacy) signatures will not be provided
for releases of Python 3.14 or future versions.
To verify CPython artifacts, users must use `Sigstore verification materials
<https://www.python.org/downloads/metadata/sigstore/>`__.
Releases have been signed using Sigstore_ since Python 3.11.

This change in release process was specified in :pep:`761`.

.. _Sigstore: https://www.sigstore.dev/


.. _whatsnew314-free-threaded-now-supported:

Free-threaded Python is officially supported
--------------------------------------------

The free-threaded build of Python is now supported and no longer experimental.
This is the start of `phase II <https://discuss.python.org/t/37075>`__ where
free-threaded Python is officially supported but still optional.

The free-threading team are confident that the project is on the right path,
and appreciate the continued dedication from everyone working to make
free-threading ready for broader adoption across the Python community.

With these recommendations and the acceptance of this PEP, the Python developer
community should broadly advertise that free-threading is a supported
Python build option now and into the future, and that it will not be removed
without a proper deprecation schedule.

Any decision to transition to `phase III <https://discuss.python.org/t/37075>`__,
with free-threading as the default or sole build of Python is still undecided,
and dependent on many factors both within CPython itself and the community.
This decision is for the future.

.. seealso::

   :pep:`779`

   `PEP 779's acceptance <https://discuss.python.org/t/84319/123>`__


.. _whatsnew314-jit-compiler:

Binary releases for the experimental just-in-time compiler
----------------------------------------------------------

The official macOS and Windows release binaries now include an *experimental*
just-in-time (JIT) compiler. Although it is **not** recommended for production
use, it can be tested by setting :envvar:`PYTHON_JIT=1 <PYTHON_JIT>` as an
environment variable. Downstream source builds and redistributors can use the
:option:`--enable-experimental-jit=yes-off` configuration option for similar
behavior.

The JIT is at an early stage and still in active development. As such, the
typical performance impact of enabling it can range from 10% slower to 20%
faster, depending on workload. To aid in testing and evaluation, a set of
introspection functions has been provided in the :data:`sys._jit` namespace.
:func:`sys._jit.is_available` can be used to determine if the current executable
supports JIT compilation, while :func:`sys._jit.is_enabled` can be used to tell
if JIT compilation has been enabled for the current process.

Currently, the most significant missing functionality is that native debuggers
and profilers like ``gdb`` and ``perf`` are unable to unwind through JIT frames
(Python debuggers and profilers, like :mod:`pdb` or :mod:`profile`, continue to
work without modification). Free-threaded builds do not support JIT compilation.

Please report any bugs or major performance regressions that you encounter!

.. seealso:: :pep:`744`


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
-------------------------

* On Unix platforms other than macOS, *forkserver* is now the default
  :ref:`start method <multiprocessing-start-methods>` for :mod:`multiprocessing`
  and :class:`~concurrent.futures.ProcessPoolExecutor`, instead of *fork*.

  See :ref:`(1) <whatsnew314-concurrent-futures-start-method>` and
  :ref:`(2) <whatsnew314-multiprocessing-start-method>` for details.

  If you encounter :exc:`NameError`\s or pickling errors coming out of
  :mod:`multiprocessing` or :mod:`concurrent.futures`, see the
  :ref:`forkserver restrictions <multiprocessing-programming-forkserver>`.

  This change does not affect Windows or macOS, where :ref:`'spawn'
  <multiprocessing-start-method-spawn>` remains the default start method.

* :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-deferred-annotations>` for details. While most code that interacts
  with annotations should continue to work, some undocumented details may behave
  differently.

* As part of making the :mod:`mimetypes` CLI public,
  it now exits with ``1`` on failure instead of ``0``
  and ``2`` on incorrect command-line parameters instead of ``1``.
  Error messages are now printed to stderr.

* The ``\B`` pattern in regular expression now matches the empty string
  when given as the entire pattern, which may cause behavioural changes.

* On FreeBSD, :data:`sys.platform` no longer contains the major version number.


.. _whatsnew314-porting-annotations:

Changes in annotations (:pep:`649` and :pep:`749`)
--------------------------------------------------

This section contains guidance on changes that may be needed to annotations
or Python code that interacts with or introspects annotations,
due to the changes related to :ref:`deferred evaluation of annotations
<whatsnew314-deferred-annotations>`.

In the majority of cases, working code from older versions of Python
will not require any changes.


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 once you support only Python 3.14 and newer.
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 :attr:`~object.__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.

The external :pypi:`typing_extensions` package provides partial backports
of some of the functionality of the :mod:`annotationlib` module,
such as the :class:`~annotationlib.Format` enum and
the :func:`~annotationlib.get_annotations` function.
These can be used to write cross-version code that takes advantage of
the new behavior in Python 3.14.


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

The changes in Python 3.14 are designed to rework how :attr:`!__annotations__`
works at runtime while minimizing breakage to code that contains
annotations in source code and to code that reads :attr:`!__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, only use the documented
functionality of the :mod:`annotationlib` module.

In particular, do not read annotations directly from the namespace dictionary
attribute of type objects.
Use :func:`annotationlib.get_annotate_from_class_namespace` during class
construction and :func:`annotationlib.get_annotations` afterwards.

In previous releases, it was sometimes possible to access class annotations
from an instance of an annotated class. This behavior was undocumented
and accidental, and will no longer work in Python 3.14.


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

In Python 3.7, :pep:`563` introduced the ``from __future__ import annotations``
:ref:`future statement <future>`, which turns all annotations into strings.

However, this statement is now deprecated and it is expected to be removed
in a future version of Python.
This removal will not happen until after Python 3.13 reaches its end of life
in 2029, being the last version of Python without support for deferred
evaluation of annotations.

In Python 3.14, the behavior of code using ``from __future__ import annotations``
is unchanged.


Changes in the C API
--------------------

* :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/
