What's New In Python 3.9

リリース

3.9.24

日付

10月 10, 2025

編集者

Łukasz Langa

この記事では 3.8 と比較した Python 3.9 の新機能を解説します。Python 3.9 は2020年10月5日にリリースされました。

全詳細については changelog をご覧ください。

参考

PEP 596 - Python 3.9 リリーススケジュール

概要 -- リリースハイライト

新たな文法機能:

  • PEP 584、 dict に和集合の演算子が追加されました。

  • PEP 585、標準コレクション型の型ヒントにおける総称型 (generics) の使用。

  • PEP 614、デコレータの適用における文法的制約の緩和。

新たな組み込み機能:

  • PEP 616、prefixとsuffixを削除する文字列メソッド。

標準ライブラリの新機能:

  • PEP 593、より柔軟な変数・関数アノテーション (訳注: Annotated の導入)。

  • os.pidfd_open() が追加され、レースやシグナルを使わずにプロセス管理ができるようになりました。

インタプリタの改善:

  • PEP 573, fast access to module state from methods of C extension types;

  • PEP 617、CPython における PEG (Parser Expression Grammar) ベースの新しい構文解析器の使用。

  • いくつかのPythonの組み込み型（range, tuple, set, frozenset, list, dict） を PEP 590 vectorcall を用いて高速化しました。

  • garbage collection does not block on resurrected objects;

  • いくつかのPython モジュール (_abc, audioop, _bz2, _codecs, _contextvars, _crypt, _functools, _json, _locale, math, operator, resource, time, _weakref) がPEP 489で定義されたマルチフェーズ初期化を利用するようになりました。

  • いくつかの標準ライブラリモジュール (audioop, ast, grp, _hashlib, pwd, _posixsubprocess, random, select, struct, termios, zlib) がPEP 384で定義された stable ABI を利用するようになりました。

新たなライブラリモジュール:

  • PEP 615、IANAのTime Zone Databaseが標準ライブラリの zoneinfo モジュールで提供されるようになりました。

  • an implementation of a topological sort of a graph is now provided in the new graphlib module.

リリースプロセスの変更:

  • PEP 602、CPythonは年次のリリースサイクルを採用します。

コード中の非推奨警告(DeprecationWarning)をチェックして下さい

Python 2.7がまだサポートされていた期間、Python 3の多くの機能はPython 2.7との後方互換性を保っていました。Python 2サポートの終了とともに、この後方互換性レイヤは除去されたか、間もなく除去されます。ここ数年で、それらの多くは警告 DeprecationWarning`を出すようになりました。例えば、2012年にリリースされたPython 3.3以降、``collections.abc.Mapping``の代りに``collections.Mapping``を使うと、警告:exc:`DeprecationWarning が出ます。

警告:exc:DeprecationWarning`および:exc:`PendingDeprecationWarning`を確認するために、:option:-W` ``default``コマンドラインオプションを付けて、あなたのアプリケーションをテストして下さい。あるいは、-W ``error``で警告をエラーとして扱うこともできます。サードパーティによるコードの警告を無視するには、:ref:`Warnings Filter <warning-filter>`を使うことができます。

Python 3.9は、Python 2後方互換性レイヤを提供する最後のバージョンです。このレイヤは、Pythonプロジェクトの保守管理者に、Python 2サポートを止めてPython 3.9サポートを追加する時間的な余裕を与えるためのものです。

Aliases to Abstract Base Classes in the collections module, like collections.Mapping alias to collections.abc.Mapping, are kept for one last release for backward compatibility. They will be removed from Python 3.10.

より一般的には、あなたのコードが次のバージョンのPythonと互換性を保てるよう、:ref:`Python Development Mode <devmode>`でテストするようにしてください。

注釈: Pythonのこのバージョンで、既存の多くの非推奨機能が削除されました。詳しくは :ref:`removed-in-python-39`を見て下さい。

新しい機能

辞書のマージと更新演算子

組み込みの dict クラスにマージ(|)と更新(|=)演算子が追加されました。この演算子は、辞書をマージする既存の方法 dict.update と {**d1, **d2} を補完します。

以下はプログラム例です:

>>> x = {"key1": "value1 from x", "key2": "value2 from x"}
>>> y = {"key2": "value2 from y", "key3": "value3 from y"}
>>> x | y
{'key1': 'value1 from x', 'key2': 'value2 from y', 'key3': 'value3 from y'}
>>> y | x
{'key2': 'value2 from x', 'key3': 'value3 from y', 'key1': 'value1 from x'}

詳細は PEP 584 を参照してください。(Brandt Bucher の貢献による bpo-36144)

prefixとsuffixを削除する新しい文字列メソッド

文字列から不要な prefix や suffix を簡単に削除する str.removeprefix(prefix) と str.removesuffix(suffix) が追加されました。 bytes, bytearray, collections.UserString にも同様のメソッドが追加されました。詳細は PEP 616 を参照してください。(Dennis Sweeney の貢献による bpo-39939)

標準コレクション型の型ヒントにおける総称型 (generics) の使用

型アノテーションで、typing モジュールからインポートしていた大文字の型（List や Dict）の代わりに、総称型（generics）で list や dict といった標準コレクション型が使用できるようになりました。いくつかの他の標準ライブラリの型（queue.Queue など）も総称型として使用できます。

例:

def greet_all(names: list[str]) -> None:
    for name in names:
        print("Hello", name)

詳細は PEP 585 を参照してください。(Guido van Rossum、Ethan Smith、Batuhan Taşkaya の貢献による bpo-39481)

新しいパーサー

Python 3.9は、`LL(1) <https://en.wikipedia.org/wiki/LL_parser>`_に代えて `PEG <https://en.wikipedia.org/wiki/Parsing_expression_grammar>`_に基づく新しいパーサーを採用しています。新しいパーサーのパフォーマンスは古いパーサーとほぼ同程度ですが、新しい言語の機能を設計する際に、PEGの形式主義はより柔軟です。我々は、この柔軟性をPython 3.10以降に使い始める予定です。

:mod:`ast`モジュールは、新しいパーサーを使って古いパーサーと同じASTを生成します。

Python 3.10では古いパーサーは削除され、それに依存する全ての機能(主に、長い間非推奨だった parser`モジュール)も削除されます。Python 3.9で*のみ*、コマンドラインスイッチ`(-X oldparser``)あるいは環境変数(``PYTHONOLDPARSER=1`)で、LL(1)パーサーにスイッチバックすることができます。

詳細は:pep:617`を参照してください。(Guido van Rossum,、Pablo Galindo、およびLysandros Nikolaouの貢献による :issue:`40334)

その他の言語変更

  • __import__() now raises ImportError instead of ValueError, which used to occur when a relative import went past its top-level package. (Contributed by Ngalim Siregar in bpo-37444.)

  • Python now gets the absolute path of the script filename specified on the command line (ex: python3 script.py): the __file__ attribute of the __main__ module became an absolute path, rather than a relative path. These paths now remain valid after the current directory is changed by os.chdir(). As a side effect, the traceback also displays the absolute path for __main__ module frames in this case. (Contributed by Victor Stinner in bpo-20443.)

  • In the Python Development Mode and in debug build, the encoding and errors arguments are now checked for string encoding and decoding operations. Examples: open(), str.encode() and bytes.decode().

    By default, for best performance, the errors argument is only checked at the first encoding/decoding error and the encoding argument is sometimes ignored for empty strings. (Contributed by Victor Stinner in bpo-37388.)

  • "".replace("", s, n) now returns s instead of an empty string for all non-zero n. It is now consistent with "".replace("", s). There are similar changes for bytes and bytearray objects. (Contributed by Serhiy Storchaka in bpo-28029.)

  • Any valid expression can now be used as a decorator. Previously, the grammar was much more restrictive. See PEP 614 for details. (Contributed by Brandt Bucher in bpo-39702.)

  • Improved help for the typing module. Docstrings are now shown for all special forms and special generic aliases (like Union and List). Using help() with generic alias like List[int] will show the help for the correspondent concrete type (list in this case). (Contributed by Serhiy Storchaka in bpo-40257.)

  • Parallel running of aclose() / asend() / athrow() is now prohibited, and ag_running now reflects the actual running status of the async generator. (Contributed by Yury Selivanov in bpo-30773.)

  • Unexpected errors in calling the __iter__ method are no longer masked by TypeError in the in operator and functions contains(), indexOf() and countOf() of the operator module. (Contributed by Serhiy Storchaka in bpo-40824.)

  • Unparenthesized lambda expressions can no longer be the expression part in an if clause in comprehensions and generator expressions. See bpo-41848 and bpo-43755 for details.

新たなモジュール

zoneinfo

zoneinfo モジュールにより標準ライブラリにIANAのタイムゾーンデータベースへのサポートを導入されます。zoneinfo.ZoneInfo という、システムのタイムゾーンデータを背景とした具体的な datetime.tzinfo の実装が追加されます。

以下はプログラム例です:

>>> from zoneinfo import ZoneInfo
>>> from datetime import datetime, timedelta

>>> # Daylight saving time
>>> dt = datetime(2020, 10, 31, 12, tzinfo=ZoneInfo("America/Los_Angeles"))
>>> print(dt)
2020-10-31 12:00:00-07:00
>>> dt.tzname()
'PDT'

>>> # Standard time
>>> dt += timedelta(days=7)
>>> print(dt)
2020-11-07 12:00:00-08:00
>>> print(dt.tzname())
PST

IANAデータベースが提供されていないプラットフォームでのデータの代わりの提供元として、 tzdata モジュールがファーストパーティーのパッケージとしてリリースされています。tzdataはPyPIで配信されており、CPythonコアチームによってメンテナンスされています。

参考

PEP 615 -- Support for the IANA Time Zone Database in the Standard Library

PEP作成と実装は Paul Ganssle による。

graphlib

A new module, graphlib, was added that contains the graphlib.TopologicalSorter class to offer functionality to perform topological sorting of graphs. (Contributed by Pablo Galindo, Tim Peters and Larry Hastings in bpo-17005.)

改良されたモジュール

ast

Added the indent option to dump() which allows it to produce a multiline indented output. (Contributed by Serhiy Storchaka in bpo-37995.)

Added ast.unparse() as a function in the ast module that can be used to unparse an ast.AST object and produce a string with code that would produce an equivalent ast.AST object when parsed. (Contributed by Pablo Galindo and Batuhan Taskaya in bpo-38870.)

Added docstrings to AST nodes that contains the ASDL signature used to construct that node. (Contributed by Batuhan Taskaya in bpo-39638.)

asyncio

セキュリティ上の重大な懸念により、asyncio.loop.create_datagram_endpoint() での reuse_address 引数は無効になりました。これはソケットオプション SO_REUSEADDR` のUDP における挙動が原因です。詳しくは、loop.create_datagram_endpoint() のドキュメントを参照してください。(Kyle Stanley, Antoine Pitrou, Yury Selivanov による貢献 bpo-37228)

Added a new coroutine shutdown_default_executor() that schedules a shutdown for the default executor that waits on the ThreadPoolExecutor to finish closing. Also, asyncio.run() has been updated to use the new coroutine. (Contributed by Kyle Stanley in bpo-34037.)

Added asyncio.PidfdChildWatcher, a Linux-specific child watcher implementation that polls process file descriptors. (bpo-38692)

Added a new coroutine asyncio.to_thread(). It is mainly used for running IO-bound functions in a separate thread to avoid blocking the event loop, and essentially works as a high-level version of run_in_executor() that can directly take keyword arguments. (Contributed by Kyle Stanley and Yury Selivanov in bpo-32309.)

When cancelling the task due to a timeout, asyncio.wait_for() will now wait until the cancellation is complete also in the case when timeout is <= 0, like it does with positive timeouts. (Contributed by Elvis Pranskevichus in bpo-32751.)

asyncio now raises TyperError when calling incompatible methods with an ssl.SSLSocket socket. (Contributed by Ido Michael in bpo-37404.)

compileall

Added new possibility to use hardlinks for duplicated .pyc files: hardlink_dupes parameter and --hardlink-dupes command line option. (Contributed by Lumír 'Frenzy' Balhar in bpo-40495.)

Added new options for path manipulation in resulting .pyc files: stripdir, prependdir, limit_sl_dest parameters and -s, -p, -e command line options. Added the possibility to specify the option for an optimization level multiple times. (Contributed by Lumír 'Frenzy' Balhar in bpo-38112.)

concurrent.futures

Added a new cancel_futures parameter to concurrent.futures.Executor.shutdown() that cancels all pending futures which have not started running, instead of waiting for them to complete before shutting down the executor. (Contributed by Kyle Stanley in bpo-39349.)

Removed daemon threads from ThreadPoolExecutor and ProcessPoolExecutor. This improves compatibility with subinterpreters and predictability in their shutdown processes. (Contributed by Kyle Stanley in bpo-39812.)

Workers in ProcessPoolExecutor are now spawned on demand, only when there are no available idle workers to reuse. This optimizes startup overhead and reduces the amount of lost CPU time to idle workers. (Contributed by Kyle Stanley in bpo-39207.)

curses

curses.get_escdelay(), curses.set_escdelay(), curses.get_tabsize(), curses.set_tabsize() の関数が追加されました。(Anthony Sottileによる bpo-38312 でのコントリビュート。)

datetime

The isocalendar() of datetime.date and isocalendar() of datetime.datetime methods now returns a namedtuple() instead of a tuple. (Contributed by Dong-hee Na in bpo-24416.)

distutils

The upload command now creates SHA2-256 and Blake2b-256 hash digests. It skips MD5 on platforms that block MD5 digest. (Contributed by Christian Heimes in bpo-40698.)

fcntl

Added constants F_OFD_GETLK, F_OFD_SETLK and F_OFD_SETLKW. (Contributed by Dong-hee Na in bpo-38602.)

ftplib

FTP and FTP_TLS now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259.)

gc

When the garbage collector makes a collection in which some objects resurrect (they are reachable from outside the isolated cycles after the finalizers have been executed), do not block the collection of all objects that are still unreachable. (Contributed by Pablo Galindo and Tim Peters in bpo-38379.)

Added a new function gc.is_finalized() to check if an object has been finalized by the garbage collector. (Contributed by Pablo Galindo in bpo-39322.)

hashlib

The hashlib module can now use SHA3 hashes and SHAKE XOF from OpenSSL when available. (Contributed by Christian Heimes in bpo-37630.)

Builtin hash modules can now be disabled with ./configure --without-builtin-hashlib-hashes or selectively enabled with e.g. ./configure --with-builtin-hashlib-hashes=sha3,blake2 to force use of OpenSSL based implementation. (Contributed by Christian Heimes in bpo-40479)

http

HTTPステータスコード 103 EARLY_HINTS, 418 IM_A_TEAPOT, 425 TOO_EARLY が http.HTTPStatus に追加されました。(Dong-hee Na の貢献 bpo-39509 とRoss Rhodesの貢献による bpo-39507)

IDLE と idelelib

Added option to toggle cursor blink off. (Contributed by Zackery Spytz in bpo-4603.)

Escape key now closes IDLE completion windows. (Contributed by Johnny Najera in bpo-38944.)

Added keywords to module name completion list. (Contributed by Terry J. Reedy in bpo-37765.)

New in 3.9 maintenance releases

Make IDLE invoke sys.excepthook() (when started without '-n'). User hooks were previously ignored. (Contributed by Ken Hilton in bpo-43008.)

The changes above have been backported to 3.8 maintenance releases.

Rearrange the settings dialog. Split the General tab into Windows and Shell/Ed tabs. Move help sources, which extend the Help menu, to the Extensions tab. Make space for new options and shorten the dialog. The latter makes the dialog better fit small screens. (Contributed by Terry Jan Reedy in bpo-40468.) Move the indent space setting from the Font tab to the new Windows tab. (Contributed by Mark Roseman and Terry Jan Reedy in bpo-33962.)

Apply syntax highlighting to .pyi files. (Contributed by Alex Waygood and Terry Jan Reedy in bpo-45447.)

imaplib

IMAP4 and IMAP4_SSL now have an optional timeout parameter for their constructors. Also, the open() method now has an optional timeout parameter with this change. The overridden methods of IMAP4_SSL and IMAP4_stream were applied to this change. (Contributed by Dong-hee Na in bpo-38615.)

imaplib.IMAP4.unselect() is added. imaplib.IMAP4.unselect() frees server's resources associated with the selected mailbox and returns the server to the authenticated state. This command performs the same actions as imaplib.IMAP4.close(), except that no messages are permanently removed from the currently selected mailbox. (Contributed by Dong-hee Na in bpo-40375.)

importlib

To improve consistency with import statements, importlib.util.resolve_name() now raises ImportError instead of ValueError for invalid relative import attempts. (Contributed by Ngalim Siregar in bpo-37444.)

Import loaders which publish immutable module objects can now publish immutable packages in addition to individual modules. (Contributed by Dino Viehland in bpo-39336.)

Added importlib.resources.files() function with support for subdirectories in package data, matching backport in importlib_resources version 1.5. (Contributed by Jason R. Coombs in bpo-39791.)

Refreshed importlib.metadata from importlib_metadata version 1.6.1.

inspect

attr:inspect.BoundArguments.arguments は OrderedDict から標準のdictに変更されました。(Inada Naoki の貢献による bpo-36350, bpo-39775)

ipaddress

ipaddress now supports IPv6 Scoped Addresses (IPv6 address with suffix %<scope_id>).

Scoped IPv6 addresses can be parsed using ipaddress.IPv6Address. If present, scope zone ID is available through the scope_id attribute. (Contributed by Oleksandr Pavliuk in bpo-34788.)

Starting with Python 3.9.5 the ipaddress module no longer accepts any leading zeros in IPv4 address strings. (Contributed by Christian Heimes in bpo-36384).

math

Expanded the math.gcd() function to handle multiple arguments. Formerly, it only supported two arguments. (Contributed by Serhiy Storchaka in bpo-39648.)

Added math.lcm(): return the least common multiple of specified arguments. (Contributed by Mark Dickinson, Ananthakrishnan and Serhiy Storchaka in bpo-39479 and bpo-39648.)

Added math.nextafter(): return the next floating-point value after x towards y. (Contributed by Victor Stinner in bpo-39288.)

Added math.ulp(): return the value of the least significant bit of a float. (Contributed by Victor Stinner in bpo-39310.)

multiprocessing

The multiprocessing.SimpleQueue class has a new close() method to explicitly close the queue. (Contributed by Victor Stinner in bpo-30966.)

nntplib

NNTP and NNTP_SSL now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259.)

os

:attr:`si_code`に、`~os.CLD_KILLED`と`~os.CLD_STOPPED`が追加されました。(:issue:`38493`でのDong-hee Naの貢献による)

Exposed the Linux-specific os.pidfd_open() (bpo-38692) and os.P_PIDFD (bpo-38713) for process management with file descriptors.

:func:`os.unsetenv`関数が、Windowsでも使えるようになりました。(:issue:`39413`におけるVictor Stinnerの貢献による)

:func:`os.putenv`と:func:`os.unsetenv`関数が、常に利用できるようになりました。(:issue:`39395`におけるVictor Stinnerの貢献による)

Added os.waitstatus_to_exitcode() function: convert a wait status to an exit code. (Contributed by Victor Stinner in bpo-40094.)

As of 3.9.20, os.mkdir() and os.makedirs() on Windows now support passing a mode value of 0o700 to apply access control to the new directory. This implicitly affects tempfile.mkdtemp() and is a mitigation for CVE-2024-4030. Other values for mode continue to be ignored. (Contributed by Steve Dower in gh-118486.)

pathlib

os.readlink() と同様の動作をする pathlib.Path.readlink() が追加されました。(Girts Folkmanis の貢献による bpo-30618)

pdb

On Windows now Pdb supports ~/.pdbrc. (Contributed by Tim Hopper and Dan Lidral-Porter in bpo-20523.)

poplib

POP3 and POP3_SSL now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259.)

pprint

pprint can now pretty-print types.SimpleNamespace. (Contributed by Carl Bordum Hansen in bpo-37376.)

pydoc

The documentation string is now shown not only for class, function, method etc, but for any object that has its own __doc__ attribute. (Contributed by Serhiy Storchaka in bpo-40257.)

random

ランダムなbytesを生成する random.Random.randbytes メソッドが追加されました。(Victor Stinner による貢献 bpo-40286)

signal

Exposed the Linux-specific signal.pidfd_send_signal() for sending to signals to a process using a file descriptor instead of a pid. (bpo-38712)

smtplib

SMTP and SMTP_SSL now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259.)

LMTP constructor now has an optional timeout parameter. (Contributed by Dong-hee Na in bpo-39329.)

socket

The socket module now exports the CAN_RAW_JOIN_FILTERS constant on Linux 4.1 and greater. (Contributed by Stefan Tatschner and Zackery Spytz in bpo-25780.)

The socket module now supports the CAN_J1939 protocol on platforms that support it. (Contributed by Karl Ding in bpo-40291.)

The socket module now has the socket.send_fds() and socket.recv_fds() functions. (Contributed by Joannah Nanjekye, Shinya Okano and Victor Stinner in bpo-28724.)

time

On AIX, thread_time() is now implemented with thread_cputime() which has nanosecond resolution, rather than clock_gettime(CLOCK_THREAD_CPUTIME_ID) which has a resolution of 10 ms. (Contributed by Batuhan Taskaya in bpo-40192)

sys

Added a new sys.platlibdir attribute: name of the platform-specific library directory. It is used to build the path of standard library and the paths of installed extension modules. It is equal to "lib" on most platforms. On Fedora and SuSE, it is equal to "lib64" on 64-bit platforms. (Contributed by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner in bpo-1294959.)

Previously, sys.stderr was block-buffered when non-interactive. Now stderr defaults to always being line-buffered. (Contributed by Jendrik Seipp in bpo-13601.)

tempfile

As of 3.9.20 on Windows, the default mode 0o700 used by tempfile.mkdtemp() now limits access to the new directory due to changes to os.mkdir(). This is a mitigation for CVE-2024-4030. (Contributed by Steve Dower in gh-118486.)

tracemalloc

Added tracemalloc.reset_peak() to set the peak size of traced memory blocks to the current size, to measure the peak of specific pieces of code. (Contributed by Huon Wilson in bpo-40630.)

typing

PEP 593 introduced an typing.Annotated type to decorate existing types with context-specific metadata and new include_extras parameter to typing.get_type_hints() to access the metadata at runtime. (Contributed by Till Varoquaux and Konstantin Kashin.)

unicodedata

Unicode データベースが、バージョン 13.0.0 に更新されました。(bpo-39926)

venv

The activation scripts provided by venv now all specify their prompt customization consistently by always using the value specified by __VENV_PROMPT__. Previously some scripts unconditionally used __VENV_PROMPT__, others only if it happened to be set (which was the default case), and one used __VENV_NAME__ instead. (Contributed by Brett Cannon in bpo-37663.)

xml

White space characters within attributes are now preserved when serializing xml.etree.ElementTree to XML file. EOLNs are no longer normalized to "n". This is the result of discussion about how to interpret section 2.11 of XML spec. (Contributed by Mefistotelis in bpo-39011.)

最適化

  • Optimized the idiom for assignment a temporary variable in comprehensions. Now for y in [expr] in comprehensions is as fast as a simple assignment y = expr. For example:

    sums = [s for s in [0] for x in data for s in [s + x]]

    Unlike the := operator this idiom does not leak a variable to the outer scope.

    (Contributed by Serhiy Storchaka in bpo-32856.)

  • Optimized signal handling in multithreaded applications. If a thread different than the main thread gets a signal, the bytecode evaluation loop is no longer interrupted at each bytecode instruction to check for pending signals which cannot be handled. Only the main thread of the main interpreter can handle signals.

    Previously, the bytecode evaluation loop was interrupted at each instruction until the main thread handles signals. (Contributed by Victor Stinner in bpo-40010.)

  • Optimized the subprocess module on FreeBSD using closefrom(). (Contributed by Ed Maste, Conrad Meyer, Kyle Evans, Kubilay Kocak and Victor Stinner in bpo-38061.)

  • PyLong_FromDouble() is now up to 1.87x faster for values that fit into long. (Contributed by Sergey Fedoseev in bpo-37986.)

  • A number of Python builtins (range, tuple, set, frozenset, list, dict) are now sped up by using PEP 590 vectorcall protocol. (Contributed by Dong-hee Na, Mark Shannon, Jeroen Demeyer and Petr Viktorin in bpo-37207.)

  • Optimized difference_update() for the case when the other set is much larger than the base set. (Suggested by Evgeny Kapun with code contributed by Michele Orrù in bpo-8425.)

  • Python's small object allocator (obmalloc.c) now allows (no more than) one empty arena to remain available for immediate reuse, without returning it to the OS. This prevents thrashing in simple loops where an arena could be created and destroyed anew on each iteration. (Contributed by Tim Peters in bpo-37257.)

  • floor division of float operation now has a better performance. Also the message of ZeroDivisionError for this operation is updated. (Contributed by Dong-hee Na in bpo-39434.)

  • Decoding short ASCII strings with UTF-8 and ascii codecs is now about 15% faster. (Contributed by Inada Naoki in bpo-37348.)

Here's a summary of performance improvements from Python 3.4 through Python 3.9:

Python version                       3.4     3.5     3.6     3.7     3.8    3.9
--------------                       ---     ---     ---     ---     ---    ---

Variable and attribute read access:
    read_local                       7.1     7.1     5.4     5.1     3.9    3.9
    read_nonlocal                    7.1     8.1     5.8     5.4     4.4    4.5
    read_global                     15.5    19.0    14.3    13.6     7.6    7.8
    read_builtin                    21.1    21.6    18.5    19.0     7.5    7.8
    read_classvar_from_class        25.6    26.5    20.7    19.5    18.4   17.9
    read_classvar_from_instance     22.8    23.5    18.8    17.1    16.4   16.9
    read_instancevar                32.4    33.1    28.0    26.3    25.4   25.3
    read_instancevar_slots          27.8    31.3    20.8    20.8    20.2   20.5
    read_namedtuple                 73.8    57.5    45.0    46.8    18.4   18.7
    read_boundmethod                37.6    37.9    29.6    26.9    27.7   41.1

Variable and attribute write access:
    write_local                      8.7     9.3     5.5     5.3     4.3    4.3
    write_nonlocal                  10.5    11.1     5.6     5.5     4.7    4.8
    write_global                    19.7    21.2    18.0    18.0    15.8   16.7
    write_classvar                  92.9    96.0   104.6   102.1    39.2   39.8
    write_instancevar               44.6    45.8    40.0    38.9    35.5   37.4
    write_instancevar_slots         35.6    36.1    27.3    26.6    25.7   25.8

Data structure read access:
    read_list                       24.2    24.5    20.8    20.8    19.0   19.5
    read_deque                      24.7    25.5    20.2    20.6    19.8   20.2
    read_dict                       24.3    25.7    22.3    23.0    21.0   22.4
    read_strdict                    22.6    24.3    19.5    21.2    18.9   21.5

Data structure write access:
    write_list                      27.1    28.5    22.5    21.6    20.0   20.0
    write_deque                     28.7    30.1    22.7    21.8    23.5   21.7
    write_dict                      31.4    33.3    29.3    29.2    24.7   25.4
    write_strdict                   28.4    29.9    27.5    25.2    23.1   24.5

Stack (or queue) operations:
    list_append_pop                 93.4   112.7    75.4    74.2    50.8   50.6
    deque_append_pop                43.5    57.0    49.4    49.2    42.5   44.2
    deque_append_popleft            43.7    57.3    49.7    49.7    42.8   46.4

Timing loop:
    loop_overhead                    0.5     0.6     0.4     0.3     0.3    0.3

These results were generated from the variable access benchmark script at: Tools/scripts/var_access_benchmark.py. The benchmark script displays timings in nanoseconds. The benchmarks were measured on an Intel® Core™ i7-4960HQ processor running the macOS 64-bit builds found at python.org.

非推奨

  • distutilsの``bdist_msi``コマンドは、現在非推奨です。代わりに、``bdist_wheel``(wheelパッケージ)を使って下さい。 ( :issue:`39586`でのHugo van Kemenadeによる貢献による)

  • Currently math.factorial() accepts float instances with non-negative integer values (like 5.0). It raises a ValueError for non-integral and negative floats. It is now deprecated. In future Python versions it will raise a TypeError for all floats. (Contributed by Serhiy Storchaka in bpo-37315.)

  • The parser and symbol modules are deprecated and will be removed in future versions of Python. For the majority of use cases, users can leverage the Abstract Syntax Tree (AST) generation and compilation stage, using the ast module.

  • The Public C API functions PyParser_SimpleParseStringFlags(), PyParser_SimpleParseStringFlagsFilename(), PyParser_SimpleParseFileFlags() and PyNode_Compile() are deprecated and will be removed in Python 3.10 together with the old parser.

  • Using NotImplemented in a boolean context has been deprecated, as it is almost exclusively the result of incorrect rich comparator implementations. It will be made a TypeError in a future version of Python. (Contributed by Josh Rosenberg in bpo-35712.)

  • The random module currently accepts any hashable type as a possible seed value. Unfortunately, some of those types are not guaranteed to have a deterministic hash value. After Python 3.9, the module will restrict its seeds to None, int, float, str, bytes, and bytearray.

  • Opening the GzipFile file for writing without specifying the mode argument is deprecated. In future Python versions it will always be opened for reading by default. Specify the mode argument for opening it for writing and silencing a warning. (Contributed by Serhiy Storchaka in bpo-28286.)

  • Deprecated the split() method of _tkinter.TkappType in favour of the splitlist() method which has more consistent and predicable behavior. (Contributed by Serhiy Storchaka in bpo-38371.)

  • The explicit passing of coroutine objects to asyncio.wait() has been deprecated and will be removed in version 3.11. (Contributed by Yury Selivanov and Kyle Stanley in bpo-34790.)

  • binhex4 and hexbin4 standards are now deprecated. The binhex module and the following binascii functions are now deprecated:

    (Contributed by Victor Stinner in bpo-39353.)

  • ast classes slice, Index and ExtSlice are considered deprecated and will be removed in future Python versions. value itself should be used instead of Index(value). Tuple(slices, Load()) should be used instead of ExtSlice(slices). (Contributed by Serhiy Storchaka in bpo-34822.)

  • ast classes Suite, Param, AugLoad and AugStore are considered deprecated and will be removed in future Python versions. They were not generated by the parser and not accepted by the code generator in Python 3. (Contributed by Batuhan Taskaya in bpo-39639 and bpo-39969 and Serhiy Storchaka in bpo-39988.)

  • The PyEval_InitThreads() and PyEval_ThreadsInitialized() functions are now deprecated and will be removed in Python 3.11. Calling PyEval_InitThreads() now does nothing. The GIL is initialized by Py_Initialize() since Python 3.7. (Contributed by Victor Stinner in bpo-39877.)

  • Passing None as the first argument to the shlex.split() function has been deprecated. (Contributed by Zackery Spytz in bpo-33262.)

  • smtpd.MailmanProxy() は、外部モジュールである mailman がないと使えないため、非推奨となりました。 (Samuel Colvinの貢献による bpo-35800)

  • lib2to3 モジュールは PendingDeprecationWarning を出力するようになりました。Python 3.9 では PEG パーサーに切り替わりました (PEP 617 参照)。Python 3.10 では lib2to3 の LL(1) パーサーでは解析できない新しい言語構文が含まれる可能性があります。 lib2to3 モジュールは、将来の Python のバージョンで標準ライブラリから削除されるかもしれません。 LibCST や parso のようなサードパーティの代替品を検討してみてください。(Carl Meyer の貢献による bpo-40360)

  • random.shuffle() の*random* パラメータは非推奨になりました。(Raymond Hettingerの貢献による bpo-40465)

削除

  • unittest.mock.__version__ における誤ったバージョン表記は削除されました。

  • nntplib.NNTP: xpath() and xgtitle() methods have been removed. These methods are deprecated since Python 3.3. Generally, these extensions are not supported or not enabled by NNTP server administrators. For xgtitle(), please use nntplib.NNTP.descriptions() or nntplib.NNTP.description() instead. (Contributed by Dong-hee Na in bpo-39366.)

  • array.array: tostring() and fromstring() methods have been removed. They were aliases to tobytes() and frombytes(), deprecated since Python 3.2. (Contributed by Victor Stinner in bpo-38916.)

  • The undocumented sys.callstats() function has been removed. Since Python 3.7, it was deprecated and always returned None. It required a special build option CALL_PROFILE which was already removed in Python 3.7. (Contributed by Victor Stinner in bpo-37414.)

  • The sys.getcheckinterval() and sys.setcheckinterval() functions have been removed. They were deprecated since Python 3.2. Use sys.getswitchinterval() and sys.setswitchinterval() instead. (Contributed by Victor Stinner in bpo-37392.)

  • The C function PyImport_Cleanup() has been removed. It was documented as: "Empty the module table. For internal use only." (Contributed by Victor Stinner in bpo-36710.)

  • _dummy_thread and dummy_threading modules have been removed. These modules were deprecated since Python 3.7 which requires threading support. (Contributed by Victor Stinner in bpo-37312.)

  • aifc.openfp() alias to aifc.open(), sunau.openfp() alias to sunau.open(), and wave.openfp() alias to wave.open() have been removed. They were deprecated since Python 3.7. (Contributed by Victor Stinner in bpo-37320.)

  • The isAlive() method of threading.Thread has been removed. It was deprecated since Python 3.8. Use is_alive() instead. (Contributed by Dong-hee Na in bpo-37804.)

  • Methods getchildren() and getiterator() of classes ElementTree and Element in the ElementTree module have been removed. They were deprecated in Python 3.2. Use iter(x) or list(x) instead of x.getchildren() and x.iter() or list(x.iter()) instead of x.getiterator(). (Contributed by Serhiy Storchaka in bpo-36543.)

  • The old plistlib API has been removed, it was deprecated since Python 3.4. Use the load(), loads(), dump(), and dumps() functions. Additionally, the use_builtin_types parameter was removed, standard bytes objects are always used instead. (Contributed by Jon Janzen in bpo-36409.)

  • The C function PyGen_NeedsFinalizing has been removed. It was not documented, tested, or used anywhere within CPython after the implementation of PEP 442. Patch by Joannah Nanjekye. (Contributed by Joannah Nanjekye in bpo-15088)

  • base64.encodestring() and base64.decodestring(), aliases deprecated since Python 3.1, have been removed: use base64.encodebytes() and base64.decodebytes() instead. (Contributed by Victor Stinner in bpo-39351.)

  • fractions.gcd() function has been removed, it was deprecated since Python 3.5 (bpo-22486): use math.gcd() instead. (Contributed by Victor Stinner in bpo-39350.)

  • The buffering parameter of bz2.BZ2File has been removed. Since Python 3.0, it was ignored and using it emitted a DeprecationWarning. Pass an open file object to control how the file is opened. (Contributed by Victor Stinner in bpo-39357.)

  • The encoding parameter of json.loads() has been removed. As of Python 3.1, it was deprecated and ignored; using it has emitted a DeprecationWarning since Python 3.8. (Contributed by Inada Naoki in bpo-39377)

  • with (await asyncio.lock): and with (yield from asyncio.lock): statements are not longer supported, use async with lock instead. The same is correct for asyncio.Condition and asyncio.Semaphore. (Contributed by Andrew Svetlov in bpo-34793.)

  • The sys.getcounts() function, the -X showalloccount command line option and the show_alloc_count field of the C structure PyConfig have been removed. They required a special Python build by defining COUNT_ALLOCS macro. (Contributed by Victor Stinner in bpo-39489.)

  • The _field_types attribute of the typing.NamedTuple class has been removed. It was deprecated since Python 3.8. Use the __annotations__ attribute instead. (Contributed by Serhiy Storchaka in bpo-40182.)

  • The symtable.SymbolTable.has_exec() method has been removed. It was deprecated since 2006, and only returning False when it's called. (Contributed by Batuhan Taskaya in bpo-40208)

  • The asyncio.Task.current_task() and asyncio.Task.all_tasks() have been removed. They were deprecated since Python 3.7 and you can use asyncio.current_task() and asyncio.all_tasks() instead. (Contributed by Rémi Lapeyre in bpo-40967)

  • The unescape() method in the html.parser.HTMLParser class has been removed (it was deprecated since Python 3.4). html.unescape() should be used for converting character references to the corresponding unicode characters.

Python 3.9への移植

このセクションでは前述の変更とバグフィックスにより必要となるかもしれないコードの変更を列挙します:

Python API の変更

  • __import__() and importlib.util.resolve_name() now raise ImportError where it previously raised ValueError. Callers catching the specific exception type and supporting both Python 3.9 and earlier versions will need to catch both using except (ImportError, ValueError):.

  • The venv activation scripts no longer special-case when __VENV_PROMPT__ is set to "".

  • The select.epoll.unregister() method no longer ignores the EBADF error. (Contributed by Victor Stinner in bpo-39239.)

  • The compresslevel parameter of bz2.BZ2File became keyword-only, since the buffering parameter has been removed. (Contributed by Victor Stinner in bpo-39357.)

  • Simplified AST for subscription. Simple indices will be represented by their value, extended slices will be represented as tuples. Index(value) will return a value itself, ExtSlice(slices) will return Tuple(slices, Load()). (Contributed by Serhiy Storchaka in bpo-34822.)

  • The importlib module now ignores the PYTHONCASEOK environment variable when the -E or -I command line options are being used.

  • The encoding parameter has been added to the classes ftplib.FTP and ftplib.FTP_TLS as a keyword-only parameter, and the default encoding is changed from Latin-1 to UTF-8 to follow RFC 2640.

  • asyncio.loop.shutdown_default_executor() has been added to AbstractEventLoop, meaning alternative event loops that inherit from it should have this method defined. (Contributed by Kyle Stanley in bpo-34037.)

  • The constant values of future flags in the __future__ module is updated in order to prevent collision with compiler flags. Previously PyCF_ALLOW_TOP_LEVEL_AWAIT was clashing with CO_FUTURE_DIVISION. (Contributed by Batuhan Taskaya in bpo-39562)

  • array('u') now uses wchar_t as C type instead of Py_UNICODE. This change doesn't affect to its behavior because Py_UNICODE is alias of wchar_t since Python 3.3. (Contributed by Inada Naoki in bpo-34538.)

  • The logging.getLogger() API now returns the root logger when passed the name 'root', whereas previously it returned a non-root logger named 'root'. This could affect cases where user code explicitly wants a non-root logger named 'root', or instantiates a logger using logging.getLogger(__name__) in some top-level module called 'root.py'. (Contributed by Vinay Sajip in bpo-37742.)

  • Division handling of PurePath now returns NotImplemented instead of raising a TypeError when passed something other than an instance of str or PurePath. This allows creating compatible classes that don't inherit from those mentioned types. (Contributed by Roger Aiudi in bpo-34775).

  • Starting with Python 3.9.5 the ipaddress module no longer accepts any leading zeros in IPv4 address strings. Leading zeros are ambiguous and interpreted as octal notation by some libraries. For example the legacy function socket.inet_aton() treats leading zeros as octal notatation. glibc implementation of modern inet_pton() does not accept any leading zeros. (Contributed by Christian Heimes in bpo-36384).

  • codecs.lookup() now normalizes the encoding name the same way as encodings.normalize_encoding(), except that codecs.lookup() also converts the name to lower case. For example, "latex+latin1" encoding name is now normalized to "latex_latin1". (Contributed by Jordon Xu in bpo-37751.)

C API の変更

  • Instances of heap-allocated types (such as those created with PyType_FromSpec() and similar APIs) hold a reference to their type object since Python 3.8. As indicated in the "Changes in the C API" of Python 3.8, for the vast majority of cases, there should be no side effect but for types that have a custom tp_traverse function, ensure that all custom tp_traverse functions of heap-allocated types visit the object's type.

    例:

    int
foo_traverse(foo_struct *self, visitproc visit, void *arg) {
// Rest of the traverse function
#if PY_VERSION_HEX >= 0x03090000
    // This was not needed before Python 3.9 (Python issue 35810 and 40217)
    Py_VISIT(Py_TYPE(self));
#endif
}

    If your traverse function delegates to tp_traverse of its base class (or another type), ensure that Py_TYPE(self) is visited only once. Note that only heap types are expected to visit the type in tp_traverse.

    For example, if your tp_traverse function includes:

    base->tp_traverse(self, visit, arg)

    then add:

    #if PY_VERSION_HEX >= 0x03090000
    // This was not needed before Python 3.9 (Python issue 35810 and 40217)
    if (base->tp_flags & Py_TPFLAGS_HEAPTYPE) {
        // a heap type's tp_traverse already visited Py_TYPE(self)
    } else {
        Py_VISIT(Py_TYPE(self));
    }
#else

    (See bpo-35810 and bpo-40217 for more information.)

  • The functions PyEval_CallObject, PyEval_CallFunction, PyEval_CallMethod and PyEval_CallObjectWithKeywords are deprecated. Use PyObject_Call() and its variants instead. (See more details in bpo-29548.)

CPython バイトコードの変更

  • The LOAD_ASSERTION_ERROR opcode was added for handling the assert statement. Previously, the assert statement would not work correctly if the AssertionError exception was being shadowed. (Contributed by Zackery Spytz in bpo-34880.)

  • The COMPARE_OP opcode was split into four distinct instructions:

    • COMPARE_OP for rich comparisons

    • IS_OP for 'is' and 'is not' tests

    • CONTAINS_OP for 'in' and 'not in' tests

    • JUMP_IF_NOT_EXC_MATCH for checking exceptions in 'try-except' statements.

    (Contributed by Mark Shannon in bpo-39156.)

Build Changes

  • Added --with-platlibdir option to the configure script: name of the platform-specific library directory, stored in the new sys.platlibdir attribute. See sys.platlibdir attribute for more information. (Contributed by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner in bpo-1294959.)

  • The COUNT_ALLOCS special build macro has been removed. (Contributed by Victor Stinner in bpo-39489.)

  • On non-Windows platforms, the setenv() and unsetenv() functions are now required to build Python. (Contributed by Victor Stinner in bpo-39395.)

  • On non-Windows platforms, creating bdist_wininst installers is now officially unsupported. (See bpo-10945 for more details.)

  • When building Python on macOS from source, _tkinter now links with non-system Tcl and Tk frameworks if they are installed in /Library/Frameworks, as had been the case on older releases of macOS. If a macOS SDK is explicitly configured, by using --enable-universalsdk= or -isysroot, only the SDK itself is searched. The default behavior can still be overridden with --with-tcltk-includes and --with-tcltk-libs. (Contributed by Ned Deily in bpo-34956.)

  • Python can now be built for Windows 10 ARM64. (Contributed by Steve Dower in bpo-33125.)

  • Some individual tests are now skipped when --pgo is used. The tests in question increased the PGO task time significantly and likely didn't help improve optimization of the final executable. This speeds up the task by a factor of about 15x. Running the full unit test suite is slow. This change may result in a slightly less optimized build since not as many code branches will be executed. If you are willing to wait for the much slower build, the old behavior can be restored using ./configure [..] PROFILE_TASK="-m test --pgo-extended". We make no guarantees as to which PGO task set produces a faster build. Users who care should run their own relevant benchmarks as results can depend on the environment, workload, and compiler tool chain. (See bpo-36044 and bpo-37707 for more details.)

C API の変更

新しい機能

Python 3.9への移植

  • PyInterpreterState.eval_frame (PEP 523) now requires a new mandatory tstate parameter (PyThreadState*). (Contributed by Victor Stinner in bpo-38500.)

  • Extension modules: m_traverse, m_clear and m_free functions of PyModuleDef are no longer called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed (Py_mod_exec function). More precisely, these functions are not called if m_size is greater than 0 and the module state (as returned by PyModule_GetState()) is NULL.

    Extension modules without module state (m_size <= 0) are not affected.

  • If Py_AddPendingCall() is called in a subinterpreter, the function is now scheduled to be called from the subinterpreter, rather than being called from the main interpreter. Each subinterpreter now has its own list of scheduled calls. (Contributed by Victor Stinner in bpo-39984.)

  • The Windows registry is no longer used to initialize sys.path when the -E option is used (if PyConfig.use_environment is set to 0). This is significant when embedding Python on Windows. (Contributed by Zackery Spytz in bpo-8901.)

  • The global variable PyStructSequence_UnnamedField is now a constant and refers to a constant string. (Contributed by Serhiy Storchaka in bpo-38650.)

  • The PyGC_Head structure is now opaque. It is only defined in the internal C API (pycore_gc.h). (Contributed by Victor Stinner in bpo-40241.)

  • The Py_UNICODE_COPY, Py_UNICODE_FILL, PyUnicode_WSTR_LENGTH, PyUnicode_FromUnicode(), PyUnicode_AsUnicode(), _PyUnicode_AsUnicode, and PyUnicode_AsUnicodeAndSize() are marked as deprecated in C. They have been deprecated by PEP 393 since Python 3.3. (Contributed by Inada Naoki in bpo-36346.)

  • The Py_FatalError() function is replaced with a macro which logs automatically the name of the current function, unless the Py_LIMITED_API macro is defined. (Contributed by Victor Stinner in bpo-39882.)

  • The vectorcall protocol now requires that the caller passes only strings as keyword names. (See bpo-37540 for more information.)

  • Implementation details of a number of macros and functions are now hidden:

    (See bpo-40170 for more details.)

削除

  • Excluded PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros of pyfpe.h from the limited C API. (Contributed by Victor Stinner in bpo-38835.)

  • The tp_print slot of PyTypeObject has been removed. It was used for printing objects to files in Python 2.7 and before. Since Python 3.0, it has been ignored and unused. (Contributed by Jeroen Demeyer in bpo-36974.)

  • Changes in the limited C API (if Py_LIMITED_API macro is defined):

    • Excluded the following functions from the limited C API:

      • PyThreadState_DeleteCurrent() (Contributed by Joannah Nanjekye in bpo-37878.)

      • _Py_CheckRecursionLimit

      • _Py_NewReference()

      • _Py_ForgetReference()

      • _PyTraceMalloc_NewReference()

      • _Py_GetRefTotal()

      • The trashcan mechanism which never worked in the limited C API.

      • PyTrash_UNWIND_LEVEL

      • Py_TRASHCAN_BEGIN_CONDITION

      • Py_TRASHCAN_BEGIN

      • Py_TRASHCAN_END

      • Py_TRASHCAN_SAFE_BEGIN

      • Py_TRASHCAN_SAFE_END

    • Moved following functions and definitions to the internal C API:

      • _PyDebug_PrintTotalRefs()

      • _Py_PrintReferences()

      • _Py_PrintReferenceAddresses()

      • _Py_tracemalloc_config

      • _Py_AddToAllObjects() (specific to Py_TRACE_REFS build)

    (Contributed by Victor Stinner in bpo-38644 and bpo-39542.)

  • Removed _PyRuntime.getframe hook and removed _PyThreadState_GetFrame macro which was an alias to _PyRuntime.getframe. They were only exposed by the internal C API. Removed also PyThreadFrameGetter type. (Contributed by Victor Stinner in bpo-39946.)

  • Removed the following functions from the C API. Call PyGC_Collect() explicitly to clear all free lists. (Contributed by Inada Naoki and Victor Stinner in bpo-37340, bpo-38896 and bpo-40428.)

    • PyAsyncGen_ClearFreeLists()

    • PyContext_ClearFreeList()

    • PyDict_ClearFreeList()

    • PyFloat_ClearFreeList()

    • PyFrame_ClearFreeList()

    • PyList_ClearFreeList()

    • PyMethod_ClearFreeList() and PyCFunction_ClearFreeList(): the free lists of bound method objects have been removed.

    • PySet_ClearFreeList(): the set free list has been removed in Python 3.4.

    • PyTuple_ClearFreeList()

    • PyUnicode_ClearFreeList(): the Unicode free list has been removed in Python 3.3.

  • Removed _PyUnicode_ClearStaticStrings() function. (Contributed by Victor Stinner in bpo-39465.)

  • Removed Py_UNICODE_MATCH. It has been deprecated by PEP 393, and broken since Python 3.3. The PyUnicode_Tailmatch() function can be used instead. (Contributed by Inada Naoki in bpo-36346.)

  • Cleaned header files of interfaces defined but with no implementation. The public API symbols being removed are: _PyBytes_InsertThousandsGroupingLocale, _PyBytes_InsertThousandsGrouping, _Py_InitializeFromArgs, _Py_InitializeFromWideArgs, _PyFloat_Repr, _PyFloat_Digits, _PyFloat_DigitsInit, PyFrame_ExtendStack, _PyAIterWrapper_Type, PyNullImporter_Type, PyCmpWrapper_Type, PySortWrapper_Type, PyNoArgsFunction. (Contributed by Pablo Galindo Salgado in bpo-39372.)

Python 3.9.1 での重要な変更点

typing

The behavior of 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 respect 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 TypeError exception during equality comparisons if any of their parameters are not hashable. 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'

(:issue:`42345`でのYurii Karabasの貢献による)

macOS 11.0 (Big Sur) と Appleシリコンの Mac のサポート

As of 3.9.1, Python now fully supports building and running on macOS 11.0 (Big Sur) and on Apple Silicon Macs (based on the ARM64 architecture). A new universal build variant, universal2, is now available to natively support both ARM64 and Intel 64 in one set of executables. Binaries can also now be built on current versions of macOS to be deployed on a range of older macOS versions (tested to 10.9) while making some newer OS functions and options conditionally available based on the operating system version in use at runtime ("weaklinking").

(:issue:`41100`でのRonald OussorenとLawrence D'Annaの貢献による)

Python 3.9.2 での重要な変更点

collections.abc

collections.abc.Callable generic now flattens type parameters, similar to what 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, types.GenericAlias can now be subclassed, and a subclass will be returned when subscripting the collections.abc.Callable type. Code which accesses the arguments via typing.get_args() or __args__ need to account for this change. A DeprecationWarning may be emitted for invalid forms of parameterizing collections.abc.Callable which may have passed silently in Python 3.9.1. This DeprecationWarning will become a TypeError in Python 3.10. (Contributed by Ken Jin in bpo-42195.)

urllib.parse

Earlier Python versions allowed using both ; and & as query parameter separators in urllib.parse.parse_qs() and urllib.parse.parse_qsl(). Due to security concerns, and to conform with newer W3C recommendations, this has been changed to allow only a single separator key, with & as the default. This change also affects cgi.parse() and cgi.parse_multipart() as they use the affected functions internally. For more details, please see their respective documentation. (Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in bpo-42967.)

Python 3.9.3 での重要な変更点

A security fix alters the ftplib.FTP behavior to not trust the IPv4 address sent from the remote server when setting up a passive data channel. We reuse the ftp server IP address instead. For unusual code requiring the old behavior, set a trust_server_pasv_ipv4_address attribute on your FTP instance to True. (See bpo-43285)

Python 3.9.5での重要な変更点

urllib.parse

The presence of newline or tab characters in parts of a URL allows for some forms of attacks. Following the WHATWG specification that updates RFC 3986, ASCII newline \n, \r and tab \t characters are stripped from the URL by the parser in urllib.parse preventing such attacks. The removal characters are controlled by a new module level variable urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE. (See bpo-43882)

Notable security feature in 3.9.14

Converting between int and str in bases other than 2 (binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now raises a ValueError if the number of digits in string form is above a limit to avoid potential denial of service attacks due to the algorithmic complexity. This is a mitigation for CVE-2020-10735. This limit can be configured or disabled by environment variable, command line flag, or sys APIs. See the integer string conversion length limitation documentation. The default limit is 4300 digits in string form.

Notable Changes in 3.9.17

tarfile

  • The extraction methods in tarfile, and shutil.unpack_archive(), have a new a filter argument that allows limiting tar features than may be surprising or dangerous, such as creating files outside the destination directory. See Extraction filters for details. In Python 3.12, use without the filter argument will show a DeprecationWarning. In Python 3.14, the default will switch to 'data'. (Contributed by Petr Viktorin in PEP 706.)

Notable changes in 3.9.20

ipaddress

  • Fixed is_global and is_private behavior in IPv4Address, IPv6Address, IPv4Network and IPv6Network.

email

  • Headers with embedded newlines are now quoted on output.

    The generator will now refuse to serialize (write) headers that are improperly folded or delimited, such that they would be parsed as multiple headers or joined with adjacent data. If you need to turn this safety feature off, set verify_generated_headers. (Contributed by Bas Bloemsaat and Petr Viktorin in gh-121650.)

  • email.utils.getaddresses() and email.utils.parseaddr() now return ('', '') 2-tuples in more situations where invalid email addresses are encountered, instead of potentially inaccurate values. An optional strict parameter was added to these two functions: use strict=False to get the old behavior, accepting malformed inputs. getattr(email.utils, 'supports_strict_parsing', False) can be used to check if the strict paramater is available. (Contributed by Thomas Dwyer and Victor Stinner for gh-102988 to improve the CVE-2023-27043 fix.)

Notable changes in 3.9.23

os.path

  • The strict parameter was backported to os.path.realpath() to allow for tarfile to use it for security vulnerability mitigation. In particular, when strict is set to os.path.ALLOW_MISSING, errors other than 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.)

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.)

  • 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.)

  • extract() and 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, LinkFallbackError. (Contributed by Petr Viktorin for CVE 2025-4330 and CVE 2024-12718.)

  • extract() and extractall() no longer extract rejected members when errorlevel() is zero. (Contributed by Matt Prodani and Petr Viktorin in gh-112887 and CVE 2025-4435.)