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 changelog.

备注

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

New features

PEP 649: deferred evaluation of annotations

The annotations on functions, classes, and modules are no longer evaluated eagerly. Instead, annotations are stored in special-purpose annotate functions 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 annotationlib module provides tools for inspecting deferred annotations. Annotations may be evaluated in the VALUE format (which evaluates annotations to runtime values, similar to the behavior in earlier Python versions), the FORWARDREF format (which replaces undefined names with special markers), and the 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 annotationlib.get_annotations() with the FORWARDREF format, as the dataclasses module now does.

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)

Other language changes

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

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

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

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

  • super objects are now pickleable and copyable. (Contributed by Serhiy Storchaka in gh-125767.)

  • The memoryview type now supports subscription, making it a generic type. (Contributed by Brian Schubert in gh-126012.)

New modules

Improved modules

argparse

  • The default value of the program name for 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 argparse.ArgumentParser, enabling suggestions for argument choices and subparser names if mistyped by the user. (Contributed by Savannah Ostrowski in gh-124456)

ast

  • Add ast.compare() for comparing two ASTs. (Contributed by Batuhan Taskaya and Jeremy Hylton in gh-60191.)

  • Add support for 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.)

concurrent.futures

  • Add InterpreterPoolExecutor, which exposes "subinterpreters (multiple Python interpreters in the same process) to Python code. This is separate from the proposed API in PEP 734. (Contributed by Eric Snow in gh-124548.)

  • The default ProcessPoolExecutor start method (see 上下文和启动方法) changed from fork to forkserver on platforms other than macOS & Windows. If you require the threading incompatible fork start method you must explicitly request it by supplying a mp_context to concurrent.futures.ProcessPoolExecutor. (Contributed by Gregory P. Smith in gh-84559.)

ctypes

  • The layout of bit fields in Structure and Union now matches platform defaults (GCC/Clang or MVSC) more closely. In particular, fields no longer overlap. (Contributed by Matthias Görgens in gh-97702.)

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

decimal

datetime

dis

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 http.server module allow the browser to apply its default dark mode. (Contributed by Yorik Hansen in gh-123430.)

inspect

json

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

  • Enable the json module to work as a script using the -m switch: python -m json. See the JSON command-line interface documentation. (Contributed by Trey Hunner in gh-122873.)

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.)

multiprocessing

operator

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

os

pathlib

pdb

  • Hardcoded breakpoints (breakpoint() and pdb.set_trace()) now reuse the most recent Pdb instance that calls set_trace(), instead of creating a new one each time. As a result, all the instance specific data like display and commands are preserved across hardcoded breakpoints. (Contributed by Tian Gao in gh-121450.)

  • Add a new argument mode to pdb.Pdb. Disable the restart command when pdb is in inline mode. (Contributed by Tian Gao in gh-123757.)

pickle

  • Set the default protocol version on the pickle module to 5. For more details, see pickle protocols.

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

pydoc

  • Annotations in help output are now usually displayed in a format closer to that in the original source. (Contributed by Jelle Zijlstra in gh-101552.)

symtable

sys

  • The previously undocumented special function sys.getobjects(), which only exists in specialized builds of Python, may now return objects from other interpreters than the one it's called in.

unicodedata

  • The Unicode database has been updated to Unicode 16.0.0.

unittest

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

uuid

Optimizations

asyncio

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

io

  • io which provides the built-in 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. 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.)

Deprecated

Pending removal in Python 3.15

  • The import system:

    • Setting __cached__ on a module while failing to set __spec__.cached is deprecated. In Python 3.15, __cached__ will cease to be set or take into consideration by the import system or standard library. (gh-97879)

    • Setting __package__ on a module while failing to set __spec__.parent is deprecated. In Python 3.15, __package__ will cease to be set or take into consideration by the import system or standard library. (gh-97879)

  • ctypes:

    • The undocumented ctypes.SetPointerType() function has been deprecated since Python 3.13.

  • http.server:

    • The obsolete and rarely used CGIHTTPRequestHandler has been deprecated since Python 3.13. No direct replacement exists. Anything is better than CGI to interface a web server with a request handler.

    • The --cgi flag to the python -m http.server command-line interface has been deprecated since Python 3.13.

  • locale:

  • pathlib:

  • platform:

    • java_ver() has been deprecated since Python 3.13. This function is only useful for Jython support, has a confusing API, and is largely untested.

  • threading:

    • RLock() will take no arguments in Python 3.15. Passing any arguments has been deprecated since Python 3.14, as the Python version does not permit any arguments, but the C version allows any number of positional or keyword arguments, ignoring every argument.

  • types:

  • typing:

    • The undocumented keyword argument syntax for creating NamedTuple classes (for example, Point = NamedTuple("Point", x=int, y=int)) has been deprecated since Python 3.13. Use the class-based syntax or the functional syntax instead.

    • The typing.no_type_check_decorator() decorator function has been deprecated since Python 3.13. After eight years in the typing module, it has yet to be supported by any major type checker.

  • wave:

Pending removal in Python 3.16

  • The import system:

    • Setting __loader__ on a module while failing to set __spec__.loader is deprecated. In Python 3.16, __loader__ will cease to be set or taken into consideration by the import system or the standard library.

  • array:

    • The 'u' format code (wchar_t) has been deprecated in documentation since Python 3.3 and at runtime since Python 3.13. Use the 'w' format code (Py_UCS4) for Unicode characters instead.

  • asyncio:

  • builtins:

    • Bitwise inversion on boolean types, ~True or ~False has been deprecated since Python 3.12, as it produces surprising and unintuitive results (-2 and -1). Use not x instead for the logical negation of a Boolean. In the rare case that you need the bitwise inversion of the underlying integer, convert to int explicitly (~int(x)).

  • shutil:

    • The ExecError exception has been deprecated since Python 3.14. It has not been used by any function in shutil since Python 3.4, and is now an alias of RuntimeError.

  • symtable:

  • sys:

  • tarfile:

    • The undocumented and unused TarFile.tarfile attribute has been deprecated since Python 3.13.

Pending removal in future versions

The following APIs will be removed in the future, although there is currently no date scheduled for their removal.

  • argparse:

    • Nesting argument groups and nesting mutually exclusive groups are deprecated.

    • Passing the undocumented keyword argument prefix_chars to add_argument_group() is now deprecated.

    • The argparse.FileType type converter is deprecated.

  • array's 'u' format code (gh-57281)

  • builtins:

    • bool(NotImplemented).

    • Generators: throw(type, exc, tb) and athrow(type, exc, tb) signature is deprecated: use throw(exc) and athrow(exc) instead, the single argument signature.

    • Currently Python accepts numeric literals immediately followed by keywords, for example 0in x, 1or x, 0if 1else 2. It allows confusing and ambiguous expressions like [0x1for x in y] (which can be interpreted as [0x1 for x in y] or [0x1f or x in y]). A syntax warning is raised if the numeric literal is immediately followed by one of keywords and, else, for, if, in, is and or. In a future release it will be changed to a syntax error. (gh-87999)

    • Support for __index__() and __int__() method returning non-int type: these methods will be required to return an instance of a strict subclass of int.

    • Support for __float__() method returning a strict subclass of float: these methods will be required to return an instance of float.

    • Support for __complex__() method returning a strict subclass of complex: these methods will be required to return an instance of complex.

    • Delegation of int() to __trunc__() method.

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

  • calendar: calendar.January and calendar.February constants are deprecated and replaced by calendar.JANUARY and calendar.FEBRUARY. (Contributed by Prince Roshan in gh-103636.)

  • codeobject.co_lnotab: use the codeobject.co_lines() method instead.

  • datetime:

    • utcnow(): use datetime.datetime.now(tz=datetime.UTC).

    • utcfromtimestamp(): use datetime.datetime.fromtimestamp(timestamp, tz=datetime.UTC).

  • gettext: Plural value must be an integer.

  • importlib:

    • load_module() method: use exec_module() instead.

    • cache_from_source() debug_override parameter is deprecated: use the optimization parameter instead.

  • importlib.metadata:

    • EntryPoints tuple interface.

    • Implicit None on return values.

  • logging: the warn() method has been deprecated since Python 3.3, use warning() instead.

  • mailbox: Use of StringIO input and text mode is deprecated, use BytesIO and binary mode instead.

  • os: Calling os.register_at_fork() in multi-threaded process.

  • pydoc.ErrorDuringImport: A tuple value for exc_info parameter is deprecated, use an exception instance.

  • re: More strict rules are now applied for numerical group references and group names in regular expressions. Only sequence of ASCII digits is now accepted as a numerical reference. The group name in bytes patterns and replacement strings can now only contain ASCII letters and digits and underscore. (Contributed by Serhiy Storchaka in gh-91760.)

  • sre_compile, sre_constants and sre_parse modules.

  • shutil: rmtree()'s onerror parameter is deprecated in Python 3.12; use the onexc parameter instead.

  • ssl options and protocols:

    • ssl.SSLContext without protocol argument is deprecated.

    • ssl.SSLContext: set_npn_protocols() and selected_npn_protocol() are deprecated: use ALPN instead.

    • ssl.OP_NO_SSL* options

    • ssl.OP_NO_TLS* options

    • ssl.PROTOCOL_SSLv3

    • ssl.PROTOCOL_TLS

    • ssl.PROTOCOL_TLSv1

    • ssl.PROTOCOL_TLSv1_1

    • ssl.PROTOCOL_TLSv1_2

    • ssl.TLSVersion.SSLv3

    • ssl.TLSVersion.TLSv1

    • ssl.TLSVersion.TLSv1_1

  • sysconfig.is_python_build() check_home parameter is deprecated and ignored.

  • threading methods:

  • typing.Text (gh-92332).

  • unittest.IsolatedAsyncioTestCase: it is deprecated to return a value that is not None from a test case.

  • urllib.parse deprecated functions: urlparse() instead

    • splitattr()

    • splithost()

    • splitnport()

    • splitpasswd()

    • splitport()

    • splitquery()

    • splittag()

    • splittype()

    • splituser()

    • splitvalue()

    • to_bytes()

  • urllib.request: URLopener and FancyURLopener style of invoking requests is deprecated. Use newer urlopen() functions and methods.

  • wsgiref: SimpleHandler.stdout.write() should not do partial writes.

  • xml.etree.ElementTree: Testing the truth value of an Element is deprecated. In a future release it will always return True. Prefer explicit len(elem) or elem is not None tests instead.

  • zipimport.zipimporter.load_module() is deprecated: use exec_module() instead.

Removed

argparse

  • Remove the type, choices, and metavar parameters of argparse.BooleanOptionalAction. They were deprecated since 3.12.

ast

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

    • ast.Bytes

    • ast.Ellipsis

    • ast.NameConstant

    • ast.Num

    • ast.Str

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

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

    • ast.Constant.n

    • ast.Constant.s

    Use ast.Constant.value instead.

    (Contributed by Alex Waygood in gh-119562.)

asyncio

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

    • asyncio.get_child_watcher()

    • asyncio.set_child_watcher()

    • asyncio.AbstractEventLoopPolicy.get_child_watcher()

    • asyncio.AbstractEventLoopPolicy.set_child_watcher()

    • asyncio.AbstractChildWatcher

    • asyncio.FastChildWatcher

    • asyncio.MultiLoopChildWatcher

    • asyncio.PidfdChildWatcher

    • asyncio.SafeChildWatcher

    • asyncio.ThreadedChildWatcher

    (Contributed by Kumar Aditya in gh-120804.)

  • Removed implicit creation of event loop by asyncio.get_event_loop(). It now raises a RuntimeError if there is no current event loop. (Contributed by Kumar Aditya in gh-126353.)

collections.abc

  • Remove collections.abc.ByteString. It had previously raised a DeprecationWarning since Python 3.12.

email

importlib

itertools

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

pathlib

  • Remove support for passing additional keyword arguments to pathlib.Path. In previous versions, any such arguments are ignored.

  • Remove support for passing additional positional arguments to pathlib.PurePath.relative_to() and is_relative_to(). In previous versions, any such arguments are joined onto other.

pkgutil

  • Remove deprecated pkgutil.get_loader() and pkgutil.find_loader(). These had previously raised a DeprecationWarning since Python 3.12. (Contributed by Bénédikt Tran in gh-97850.)

pty

sqlite3

typing

  • Remove typing.ByteString. It had previously raised a DeprecationWarning since Python 3.12.

urllib

Others

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

  • functools.partial is now a method descriptor. Wrap it in staticmethod() if you want to preserve the old behavior. (Contributed by Serhiy Storchaka and Dominykas Grigonis in gh-121027.)

  • The locale.nl_langinfo() function now sets temporarily the LC_CTYPE locale in some cases. This temporary change affects other threads. (Contributed by Serhiy Storchaka in gh-69998.)

Build changes

C API changes

New features

Porting to Python 3.14

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

Deprecated

  • The Py_HUGE_VAL macro is soft deprecated, use Py_INFINITY instead. (Contributed by Sergey B Kirpichev in gh-120026.)

  • Macros Py_IS_NAN, Py_IS_INFINITY and Py_IS_FINITE are soft deprecated, use instead isnan, isinf and isfinite available from math.h since C99. (Contributed by Sergey B Kirpichev in gh-119613.)

Pending removal in Python 3.15

Pending removal in future versions

The following APIs are deprecated and will be removed, although there is currently no date scheduled for their removal.

Removed