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What's new in Python 3.14

Editor:TBD

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

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

Note

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

Summary -- release highlights

Incompatible changes

On platforms other than macOS and Windows, the default :ref:`start method <multiprocessing-start-methods>` for :mod:`multiprocessing` and :class:`~concurrent.futures.ProcessPoolExecutor` switches from fork to forkserver.

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>`.

New features

PEP 649: deferred evaluation of annotations

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

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

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

This example shows how these formats behave:

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

Implications for annotated code

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

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

Implications for readers of __annotations__

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

Related changes

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

from __future__ import annotations

In Python 3.7, PEP 563 introduced the from __future__ import annotations directive, which turns all annotations into strings. This directive is now considered deprecated and it is expected to be removed in a future version of Python. However, this removal will not happen until after Python 3.13, the last version of Python without deferred evaluation of annotations, reaches its end of life in 2029. In Python 3.14, the behavior of code using from __future__ import annotations is unchanged.

Improved error messages

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

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

  • If a statement (:keyword:`pass`, :keyword:`del`, :keyword:`return`, :keyword:`yield`, :keyword:`raise`, :keyword:`break`, :keyword:`continue`, :keyword:`assert`, :keyword:`import`, :keyword:`from`) 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`.)

    >>> 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`.)

    >>> "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?

PEP 741: 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; 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 the Python initialization. This PEP unifies also the configuration of the Python preinitialization and the Python 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 simplify the API further.

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`.

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 numbers on our machines suggest anywhere from -3% to 30% faster Python code, and a geometric mean of 9-15% faster on pyperformance 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, we expect that a future release of GCC will support this as well.

This feature is opt-in for now. We highly recommend enabling profile-guided optimization with the new interpreter as it is the only configuration we have tested and can validate its improved performance. For further information on how to build Python, 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.

(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.)

Other language changes

New modules

Improved modules

argparse

ast

  • Add :func:`ast.compare` 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 repr() output for AST nodes now includes more information. (Contributed by Tomas R in :gh:`116022`.)
  • :func:`ast.parse`, when called with an AST as input, now always verifies that the root node type is appropriate. (Contributed by Irit Katriel in :gh:`130139`.)

calendar

concurrent.futures

contextvars

ctypes

datetime

decimal

difflib

dis

errno

fractions

functools

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`.)

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`.)

imaplib

inspect

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`.)

json

mimetypes

  • Add MS 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

    (Contributed by Sahil Prajapati and Hugo van Kemenade in :gh:`84852`.)

  • Add RFC 9559 MIME types for Matroska audiovisual data container structures, containing:

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

    (Contributed by Hugo van Kemenade in :gh:`89416`.)

  • Add MIME types for 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)

    (Contributed by Hugo van Kemenade in :gh:`85957`.)

  • More MIME type 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 9639: Add FLAC audio/flac (.flac)
    • De facto: Add WebM audio/webm (.weba)
    • ECMA-376: Add .docx, .pptx and .xlsx types
    • OASIS: Add OpenDocument .odg, .odp, .ods and .odt types
    • W3C: Add EPUB application/epub+zip (.epub)

    (Contributed by Hugo van Kemenade in :gh:`129965`.)

multiprocessing

operator

os

pathlib

pdb

pickle

platform

pydoc

ssl

symtable

sys

sys.monitoring

threading

tkinter

turtle

unicodedata

  • The Unicode database has been updated to Unicode 16.0.0.

unittest

urllib

uuid

zipinfo

Optimizations

asyncio

base64

io

  • :mod:`io` which provides the built-in :func:`open` makes less system calls when opening regular files as well as reading whole files. Reading a small operating system cached file in full is up to 15% faster. :func:`pathlib.Path.read_bytes` has the most optimizations for reading a file's bytes in full. (Contributed by Cody Maloney and Victor Stinner in :gh:`120754` and :gh:`90102`.)

uuid

Deprecated

Removed

argparse

ast

asyncio

collections.abc

email

importlib

itertools

pathlib

pkgutil

pty

sqlite3

typing

urllib

Others

CPython Bytecode Changes

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

Build changes

PEP 761: Discontinuation of PGP signatures

PGP signatures will not be available for CPython 3.14 and onwards. Users verifying artifacts must use Sigstore verification materials for verifying CPython artifacts. This change in release process is specified in PEP 761.

C API changes

New features

Limited C API changes

Porting to Python 3.14

Deprecated

Removed