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What's New In Python 3.10

Release:|release|
Date: |today|

This article explains the new features in Python 3.10, compared to 3.9.

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 3.10 moves towards release, so it's worth checking back even after reading earlier versions.

Summary -- Release highlights

New Features

PEP 563: Postponed Evaluation of Annotations Becomes Default

In Python 3.7, postponed evaluation of annotations was added, to be enabled with a from __future__ import annotations directive. In 3.10 this became the default behavior, even without that future directive. With this being default, all annotations stored in :attr:`__annotations__` will be strings. If needed, annotations can be resolved at runtime using :func:`typing.get_type_hints`. See PEP 563 for a full description. Also, the :func:`inspect.signature` will try to resolve types from now on, and when it fails it will fall back to showing the string annotations. (Contributed by Batuhan Taskaya in :issue:`38605`.)

PEP 613: TypeAlias Annotation

PEP 484 introduced the concept of type aliases, only requiring them to be top-level unannotated assignments. This simplicity sometimes made it difficult for type checkers to distinguish between type aliases and ordinary assignments, especially when forward references or invalid types were involved. Compare:

StrCache = 'Cache[str]'  # a type alias
LOG_PREFIX = 'LOG[DEBUG]'  # a module constant

Now the :mod:`typing` module has a special annotation :data:`TypeAlias` to declare type aliases more explicitly:

StrCache: TypeAlias = 'Cache[str]'  # a type alias
LOG_PREFIX = 'LOG[DEBUG]'  # a module constant

See PEP 613 for more details.

(Contributed by Mikhail Golubev in :issue:`41923`.)

PEP 604: New Type Union Operator

A new type union operator was introduced which enables the syntax X | Y. This provides a cleaner way of expressing 'either type X or type Y' instead of using :data:`typing.Union`, especially in type hints (annotations).

In previous versions of Python, to apply a type hint for functions accepting arguments of multiple types, :data:`typing.Union` was used:

def square(number: Union[int, float]) -> Union[int, float]:
    return number ** 2

Type hints can now be written in a more succinct manner:

def square(number: int | float) -> int | float:
    return number ** 2

See PEP 604 for more details.

(Contributed by Maggie Moss and Philippe Prados in :issue:`41428`.)

Other Language Changes

New Modules

  • None yet.

Improved Modules

base64

Add :func:`base64.b32hexencode` and :func:`base64.b32hexdecode` to support the Base32 Encoding with Extended Hex Alphabet.

codecs

Add a :func:`codecs.unregister` function to unregister a codec search function. (Contributed by Hai Shi in :issue:`41842`.)

collections.abc

The __args__ of the :ref:`parameterized generic <types-genericalias>` for :class:`collections.abc.Callable` are now consistent with :data:`typing.Callable`. :class:`collections.abc.Callable` generic now flattens type parameters, similar to what :data:`typing.Callable` currently does. This means that collections.abc.Callable[[int, str], str] will have __args__ of (int, str, str); previously this was ([int, str], str). To allow this change, :class:`types.GenericAlias` can now be subclassed, and a subclass will be returned when subscripting the :class:`collections.abc.Callable` type. Note that a :exc:`TypeError` may be raised for invalid forms of parameterizing :class:`collections.abc.Callable` which may have passed silently in Python 3.9. (Contributed by Ken Jin in :issue:`42195`.)

contextlib

Add a :func:`contextlib.aclosing` context manager to safely close async generators and objects representing asynchronously released resources. (Contributed by Joongi Kim and John Belmonte in :issue:`41229`.)

Add asynchronous context manager support to :func:`contextlib.nullcontext`. (Contributed by Tom Gringauz in :issue:`41543`.)

curses

The extended color functions added in ncurses 6.1 will be used transparently by :func:`curses.color_content`, :func:`curses.init_color`, :func:`curses.init_pair`, and :func:`curses.pair_content`. A new function, :func:`curses.has_extended_color_support`, indicates whether extended color support is provided by the underlying ncurses library. (Contributed by Jeffrey Kintscher and Hans Petter Jansson in :issue:`36982`.)

doctest

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

encodings

:func:`encodings.normalize_encoding` now ignores non-ASCII characters. (Contributed by Hai Shi in :issue:`39337`.)

glob

Added the root_dir and dir_fd parameters in :func:`~glob.glob` and :func:`~glob.iglob` which allow to specify the root directory for searching. (Contributed by Serhiy Storchaka in :issue:`38144`.)

inspect

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

Added globalns and localns parameters in :func:`~inspect.signature` and :meth:`inspect.Signature.from_callable` to retrieve the annotations in given local and global namespaces. (Contributed by Batuhan Taskaya in :issue:`41960`.)

linecache

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

os

Added :func:`os.cpu_count()` support for VxWorks RTOS. (Contributed by Peixing Xin in :issue:`41440`.)

Added a new function :func:`os.eventfd` and related helpers to wrap the eventfd2 syscall on Linux. (Contributed by Christian Heimes in :issue:`41001`.)

Added :func:`os.splice()` that allows to move data between two file descriptors without copying between kernel address space and user address space, where one of the file descriptors must refer to a pipe. (Contributed by Pablo Galindo in :issue:`41625`.)

pathlib

Added slice support to :attr:`PurePath.parents <pathlib.PurePath.parents>`. (Contributed by Joshua Cannon in :issue:`35498`)

Added negative indexing support to :attr:`PurePath.parents <pathlib.PurePath.parents>`. (Contributed by Yaroslav Pankovych in :issue:`21041`)

platform

Added :func:`platform.freedesktop_os_release()` to retrieve operation system identification from freedesktop.org os-release standard file. (Contributed by Christian Heimes in :issue:`28468`)

py_compile

Added --quiet option to command-line interface of :mod:`py_compile`. (Contributed by Gregory Schevchenko in :issue:`38731`.)

shelve

The :mod:`shelve` module now uses :data:`pickle.DEFAULT_PROTOCOL` by default instead of :mod:`pickle` protocol 3 when creating shelves. (Contributed by Zackery Spytz in :issue:`34204`.)

site

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

socket

The exception :exc:`socket.timeout` is now an alias of :exc:`TimeoutError`. (Contributed by Christian Heimes in :issue:`42413`.)

sys

Add :data:`sys.orig_argv` attribute: the list of the original command line arguments passed to the Python executable. (Contributed by Victor Stinner in :issue:`23427`.)

threading

Added :func:`threading.gettrace` and :func:`threading.getprofile` to retrieve the functions set by :func:`threading.settrace` and :func:`threading.setprofile` respectively. (Contributed by Mario Corchero in :issue:`42251`.)

Add :data:`threading.__excepthook__` to allow retrieving the original value of :func:`threading.excepthook` in case it is set to a broken or a different value. (Contributed by Mario Corchero in :issue:`42308`.)

traceback

The :func:`~traceback.format_exception`, :func:`~traceback.format_exception_only`, and :func:`~traceback.print_exception` functions can now take an exception object as a positional-only argument. (Contributed by Zackery Spytz and Matthias Bussonnier in :issue:`26389`.)

types

Reintroduced the :data:`types.EllipsisType`, :data:`types.NoneType` and :data:`types.NotImplementedType` classes, providing a new set of types readily interpretable by type checkers. (Contributed by Bas van Beek in :issue:`41810`.)

typing

The behavior of :class:`typing.Literal` was changed to conform with PEP 586 and to match the behavior of static type checkers specified in the PEP.

  1. Literal now de-duplicates parameters.

  2. Equality comparisons between Literal objects are now order independent.

  3. Literal comparisons now respects types. For example, Literal[0] == Literal[False] previously evaluated to True. It is now False. To support this change, the internally used type cache now supports differentiating types.

  4. Literal objects will now raise a :exc:`TypeError` exception during equality comparisons if one of their parameters are not :term:`immutable`. Note that declaring Literal with mutable parameters will not throw an error:

    >>> from typing import Literal
>>> Literal[{0}]
>>> Literal[{0}] == Literal[{False}]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'

(Contributed by Yurii Karabas in :issue:`42345`.)

unittest

Add new method :meth:`~unittest.TestCase.assertNoLogs` to complement the existing :meth:`~unittest.TestCase.assertLogs`. (Contributed by Kit Yan Choi in :issue:`39385`.)

xml

Add a :class:`~xml.sax.handler.LexicalHandler` class to the :mod:`xml.sax.handler` module. (Contributed by Jonathan Gossage and Zackery Spytz in :issue:`35018`.)

zipimport

Add methods related to PEP 451: :meth:`~zipimport.zipimporter.find_spec`, :meth:`zipimport.zipimporter.create_module`, and :meth:`zipimport.zipimporter.exec_module`. (Contributed by Brett Cannon in :issue:`42131`.

Optimizations

  • Constructors :func:`str`, :func:`bytes` and :func:`bytearray` are now faster (around 30--40% for small objects). (Contributed by Serhiy Storchaka in :issue:`41334`.)
  • The :mod:`runpy` module now imports fewer modules. The python3 -m module-name command startup time is 1.3x faster in average. (Contributed by Victor Stinner in :issue:`41006`.)
  • The LOAD_ATTR instruction now uses new "per opcode cache" mechanism. It is about 36% faster now. (Contributed by Pablo Galindo and Yury Selivanov in :issue:`42093`, based on ideas implemented originally in PyPy and MicroPython.)
  • When building Python with --enable-optimizations now -fno-semantic-interposition is added to both the compile and link line. This speeds builds of the Python interpreter created with --enable-shared with gcc by up to 30%. See this article for more details. (Contributed by Victor Stinner and Pablo Galindo in :issue:`38980`.)
  • Function parameters and their annotations are no longer computed at runtime, but rather at compilation time. They are stored as a tuple of strings at the bytecode level. It is now around 100% faster to create a function with parameter annotations. (Contributed by Yurii Karabas and Inada Naoki in :issue:`42202`)

Deprecated

Removed

  • Removed special methods __int__, __float__, __floordiv__, __mod__, __divmod__, __rfloordiv__, __rmod__ and __rdivmod__ of the :class:`complex` class. They always raised a :exc:`TypeError`. (Contributed by Serhiy Storchaka in :issue:`41974`.)
  • The ParserBase.error() method from the private and undocumented _markupbase module has been removed. :class:`html.parser.HTMLParser` is the only subclass of ParserBase and its error() implementation has already been removed in Python 3.5. (Contributed by Berker Peksag in :issue:`31844`.)
  • Removed the unicodedata.ucnhash_CAPI attribute which was an internal PyCapsule object. The related private _PyUnicode_Name_CAPI structure was moved to the internal C API. (Contributed by Victor Stinner in :issue:`42157`.)
  • Removed the parser module, which was deprecated in 3.9 due to the switch to the new PEG parser, as well as all the C source and header files that were only being used by the old parser, including node.h, parser.h, graminit.h and grammar.h.
  • Removed the Public C API functions :c:func:`PyParser_SimpleParseStringFlags`, :c:func:`PyParser_SimpleParseStringFlagsFilename`, :c:func:`PyParser_SimpleParseFileFlags` and :c:func:`PyNode_Compile` that were deprecated in 3.9 due to the switch to the new PEG parser.
  • Removed the formatter module, which was deprecated in Python 3.4. It is somewhat obsolete, little used, and not tested. It was originally scheduled to be removed in Python 3.6, but such removals were delayed until after Python 2.7 EOL. Existing users should copy whatever classes they use into their code. (Contributed by Dong-hee Na and Terry J. Reedy in :issue:`42299`.)
  • Removed the :c:func:`PyModule_GetWarningsModule` function that was useless now due to the _warnings module was converted to a builtin module in 2.6. (Contributed by Hai Shi in :issue:`42599`.)

Porting to Python 3.10

This section lists previously described changes and other bugfixes that may require changes to your code.

Changes in the Python API

CPython bytecode changes

  • The MAKE_FUNCTION instruction accepts tuple of strings as annotations instead of dictionary. (Contributed by Yurii Karabas and Inada Naoki in :issue:`42202`)

Build Changes

C API Changes

New Features

Porting to Python 3.10

Deprecated

Removed