What’s New In Python 3.13

Editor:

Thomas Wouters

This article explains the new features in Python 3.13, compared to 3.12.

For full details, see the changelog.

See also

PEP 719 – Python 3.13 Release Schedule

Note

Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.13 moves towards release, so it’s worth checking back even after reading earlier versions.

Summary – Release Highlights

Python 3.13 beta is the pre-release of the next version of the Python programming language, with a mix of changes to the language, the implementation and the standard library. The biggest changes to the implementation include a new interactive interpreter, and experimental support for dropping the Global Interpreter Lock (PEP 703) and a Just-In-Time compiler (PEP 744). The library changes contain removal of deprecated APIs and modules, as well as the usual improvements in user-friendliness and correctness.

Interpreter improvements:

New typing features:

Free-threading:

Platform support:

  • PEP 730: Apple’s iOS is now an officially supported platform. Official Android support (PEP 738) is in the works as well.

Removed modules:

  • PEP 594: The remaining 19 “dead batteries” have been removed from the standard library: aifc, audioop, cgi, cgitb, chunk, crypt, imghdr, mailcap, msilib, nis, nntplib, ossaudiodev, pipes, sndhdr, spwd, sunau, telnetlib, uu and xdrlib.

  • Also removed were the tkinter.tix and lib2to3 modules, and the 2to3 program.

Release schedule changes:

  • PEP 602 (“Annual Release Cycle for Python”) has been updated:

    • Python 3.9 - 3.12 have one and a half years of full support, followed by three and a half years of security fixes.

    • Python 3.13 and later have two years of full support, followed by three years of security fixes.

New Features

A Better Interactive Interpreter

On Unix-like systems like Linux or macOS as well as Windows, Python now uses a new interactive shell. When the user starts the REPL from an interactive terminal the interactive shell now supports the following new features:

  • Colorized prompts.

  • Multiline editing with history preservation.

  • Interactive help browsing using F1 with a separate command history.

  • History browsing using F2 that skips output as well as the >>> and … prompts.

  • “Paste mode” with F3 that makes pasting larger blocks of code easier (press F3 again to return to the regular prompt).

  • The ability to issue REPL-specific commands like help, exit, and quit without the need to use call parentheses after the command name.

If the new interactive shell is not desired, it can be disabled via the PYTHON_BASIC_REPL environment variable.

The new shell requires curses on Unix-like systems.

For more on interactive mode, see Interactive Mode.

(Contributed by Pablo Galindo Salgado, Łukasz Langa, and Lysandros Nikolaou in gh-111201 based on code from the PyPy project. Windows support contributed by Dino Viehland and Anthony Shaw.)

Improved Error Messages

  • The interpreter now colorizes error messages when displaying tracebacks by default. This feature can be controlled via the new PYTHON_COLORS environment variable as well as the canonical NO_COLOR and FORCE_COLOR environment variables. See also Controlling color. (Contributed by Pablo Galindo Salgado in gh-112730.)

  • A common mistake is to write a script with the same name as a standard library module. When this results in errors, we now display a more helpful error message:

    $ python random.py
Traceback (most recent call last):
  File "/home/random.py", line 1, in <module>
    import random; print(random.randint(5))
    ^^^^^^^^^^^^^
  File "/home/random.py", line 1, in <module>
    import random; print(random.randint(5))
                        ^^^^^^^^^^^^^^
AttributeError: module 'random' has no attribute 'randint' (consider renaming '/home/random.py' since it has the same name as the standard library module named 'random' and the import system gives it precedence)

    Similarly, if a script has the same name as a third-party module it attempts to import, and this results in errors, we also display a more helpful error message:

    $ python numpy.py
Traceback (most recent call last):
  File "/home/numpy.py", line 1, in <module>
    import numpy as np; np.array([1,2,3])
    ^^^^^^^^^^^^^^^^^^
  File "/home/numpy.py", line 1, in <module>
    import numpy as np; np.array([1,2,3])
                        ^^^^^^^^
AttributeError: module 'numpy' has no attribute 'array' (consider renaming '/home/numpy.py' if it has the same name as a third-party module you intended to import)

    (Contributed by Shantanu Jain in gh-95754.)

  • When an incorrect keyword argument is passed to a function, the error message now potentially suggests the correct keyword argument. (Contributed by Pablo Galindo Salgado and Shantanu Jain in gh-107944.)

    >>> "better error messages!".split(max_split=1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    "better error messages!".split(max_split=1)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
TypeError: split() got an unexpected keyword argument 'max_split'. Did you mean 'maxsplit'?

  • Classes have a new __static_attributes__ attribute, populated by the compiler, with a tuple of names of attributes of this class which are accessed through self.X from any function in its body. (Contributed by Irit Katriel in gh-115775.)

Defined mutation semantics for locals()

Historically, the expected result of mutating the return value of locals() has been left to individual Python implementations to define.

Through PEP 667, Python 3.13 standardises the historical behaviour of CPython for most code execution scopes, but changes optimized scopes (functions, generators, coroutines, comprehensions, and generator expressions) to explicitly return independent snapshots of the currently assigned local variables, including locally referenced nonlocal variables captured in closures.

This change to the semantics of locals() in optimized scopes also affects the default behaviour of code execution functions that implicitly target locals() if no explicit namespace is provided (such as exec() and eval()). In previous versions, whether or not changes could be accessed by calling locals() after calling the code execution function was implementation dependent. In CPython specifically, such code would typically appear to work as desired, but could sometimes fail in optimized scopes based on other code (including debuggers and code execution tracing tools) potentially resetting the shared snapshot in that scope. Now, the code will always run against an independent snapshot of the local variables in optimized scopes, and hence the changes will never be visible in subsequent calls to locals(). To access the changes made in these cases, an explicit namespace reference must now be passed to the relevant function. Alternatively, it may make sense to update affected code to use a higher level code execution API that returns the resulting code execution namespace (e.g. runpy.run_path() when executing Python files from disk).

To ensure debuggers and similar tools can reliably update local variables in scopes affected by this change, FrameType.f_locals now returns a write-through proxy to the frame’s local and locally referenced nonlocal variables in these scopes, rather than returning an inconsistently updated shared dict instance with undefined runtime semantics.

See PEP 667 for more details, including related C API changes and deprecations. Porting notes are also provided below for the affected Python APIs and C APIs.

(PEP and implementation contributed by Mark Shannon and Tian Gao in gh-74929. Documentation updates provided by Guido van Rossum and Alyssa Coghlan.)

Incremental Garbage Collection

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

Support For Mobile Platforms

  • iOS is now a PEP 11 supported platform. arm64-apple-ios (iPhone and iPad devices released after 2013) and arm64-apple-ios-simulator (Xcode iOS simulator running on Apple Silicon hardware) are now tier 3 platforms.

    x86_64-apple-ios-simulator (Xcode iOS simulator running on older x86_64 hardware) is not a tier 3 supported platform, but will be supported on a best-effort basis.

    See PEP 730: for more details.

    (PEP written and implementation contributed by Russell Keith-Magee in gh-114099.)

Experimental JIT Compiler

When CPython is configured using the --enable-experimental-jit option, a just-in-time compiler is added which may speed up some Python programs.

The internal architecture is roughly as follows.

  • We start with specialized Tier 1 bytecode. See What’s new in 3.11 for details.

  • When the Tier 1 bytecode gets hot enough, it gets translated to a new, purely internal Tier 2 IR, a.k.a. micro-ops (“uops”).

  • The Tier 2 IR uses the same stack-based VM as Tier 1, but the instruction format is better suited to translation to machine code.

  • We have several optimization passes for Tier 2 IR, which are applied before it is interpreted or translated to machine code.

  • There is a Tier 2 interpreter, but it is mostly intended for debugging the earlier stages of the optimization pipeline. The Tier 2 interpreter can be enabled by configuring Python with --enable-experimental-jit=interpreter.

  • When the JIT is enabled, the optimized Tier 2 IR is translated to machine code, which is then executed.

  • The machine code translation process uses a technique called copy-and-patch. It has no runtime dependencies, but there is a new build-time dependency on LLVM.

The --enable-experimental-jit flag has the following optional values:

  • no (default) – Disable the entire Tier 2 and JIT pipeline.

  • yes (default if the flag is present without optional value) – Enable the JIT. To disable the JIT at runtime, pass the environment variable PYTHON_JIT=0.

  • yes-off – Build the JIT but disable it by default. To enable the JIT at runtime, pass the environment variable PYTHON_JIT=1.

  • interpreter – Enable the Tier 2 interpreter but disable the JIT. The interpreter can be disabled by running with PYTHON_JIT=0.

(On Windows, use PCbuild/build.bat --experimental-jit to enable the JIT or --experimental-jit-interpreter to enable the Tier 2 interpreter.)

See PEP 744 for more details.

(JIT by Brandt Bucher, inspired by a paper by Haoran Xu and Fredrik Kjolstad. Tier 2 IR by Mark Shannon and Guido van Rossum. Tier 2 optimizer by Ken Jin.)

Free-threaded CPython

CPython will run with the global interpreter lock (GIL) disabled when configured using the --disable-gil option at build time. This is an experimental feature and therefore isn’t used by default. Users need to either compile their own interpreter, or install one of the experimental builds that are marked as free-threaded. See PEP 703 “Making the Global Interpreter Lock Optional in CPython” for more detail.

Free-threaded execution allows for full utilization of the available processing power by running threads in parallel on available CPU cores. While not all software will benefit from this automatically, programs designed with threading in mind will run faster on multicore hardware.

Work is still ongoing: expect some bugs and a substantial single-threaded performance hit.

The free-threaded build still supports optionally running with the GIL enabled at runtime using the environment variable PYTHON_GIL or the command line option -X gil.

To check if the current interpreter is configured with --disable-gil, use sysconfig.get_config_var("Py_GIL_DISABLED"). To check if the GIL is actually disabled in the running process, the sys._is_gil_enabled() function can be used.

C-API extension modules need to be built specifically for the free-threaded build. Extensions that support running with the GIL disabled should use the Py_mod_gil slot. Extensions using single-phase init should use PyUnstable_Module_SetGIL() to indicate whether they support running with the GIL disabled. Importing C extensions that don’t use these mechanisms will cause the GIL to be enabled, unless the GIL was explicitly disabled with the PYTHON_GIL environment variable or the -X gil=0 option.

pip 24.1b1 or newer is required to install packages with C extensions in the free-threaded build.

Other Language Changes

New Modules

  • None.

Improved Modules

argparse

  • Add parameter deprecated in methods add_argument() and add_parser() which allows to deprecate command-line options, positional arguments and subcommands. (Contributed by Serhiy Storchaka in gh-83648.)

array

  • Add 'w' type code (Py_UCS4) that can be used for Unicode strings. It can be used instead of 'u' type code, which is deprecated. (Contributed by Inada Naoki in gh-80480.)

  • Add clear() method in order to implement MutableSequence. (Contributed by Mike Zimin in gh-114894.)

ast

  • The constructors of node types in the ast module are now stricter in the arguments they accept, and have more intuitive behaviour when arguments are omitted.

    If an optional field on an AST node is not included as an argument when constructing an instance, the field will now be set to None. Similarly, if a list field is omitted, that field will now be set to an empty list, and if a ast.expr_context field is omitted, it defaults to Load(). (Previously, in all cases, the attribute would be missing on the newly constructed AST node instance.)

    If other arguments are omitted, a DeprecationWarning is emitted. This will cause an exception in Python 3.15. Similarly, passing a keyword argument that does not map to a field on the AST node is now deprecated, and will raise an exception in Python 3.15.

    These changes do not apply to user-defined subclasses of ast.AST, unless the class opts in to the new behavior by setting the attribute ast.AST._field_types.

    (Contributed by Jelle Zijlstra in gh-105858, gh-117486, and gh-118851.)

  • ast.parse() now accepts an optional argument optimize which is passed on to the compile() built-in. This makes it possible to obtain an optimized AST. (Contributed by Irit Katriel in gh-108113.)

asyncio

base64

copy

ctypes

  • The layout of bit fields in Structure and Union was improved to better match platform defaults (GCC/Clang or MSC). In particular, fields no longer overlap. (Contributed by Matthias Görgens in gh-97702.)

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

dbm

dis

  • Change the output of dis module functions to show logical labels for jump targets and exception handlers, rather than offsets. The offsets can be added with the new -O command line option or the show_offsets parameter. (Contributed by Irit Katriel in gh-112137.)

  • get_instructions() no longer represents cache entries as separate instructions. Instead, it returns them as part of the Instruction, in the new cache_info field. The show_caches argument to get_instructions() is deprecated and no longer has any effect. (Contributed by Irit Katriel in gh-112962.)

doctest

email

  • 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. Add optional strict parameter to these two functions: use strict=False to get the old behavior, accept malformed inputs. getattr(email.utils, 'supports_strict_parsing', False) can be used to check if the strict parameter is available. (Contributed by Thomas Dwyer and Victor Stinner for gh-102988 to improve the CVE-2023-27043 fix.)

fractions

  • Formatting for objects of type fractions.Fraction now supports the standard format specification mini-language rules for fill, alignment, sign handling, minimum width and grouping. (Contributed by Mark Dickinson in gh-111320.)

gc

  • The cyclic garbage collector is now incremental, which changes the meanings of the results of gc.get_threshold() and gc.set_threshold() as well as gc.get_count() and gc.get_stats().

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

    • gc.set_threshold() ignores any items after the second.

    • gc.get_count() and gc.get_stats() return the same format of results as before. The only difference is that instead of the results referring to the young, aging and old generations, the results refer to the young generation and the aging and collecting spaces of the old generation.

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

glob

  • Add glob.translate() function that converts a path specification with shell-style wildcards to a regular expression. (Contributed by Barney Gale in gh-72904.)

importlib

io

ipaddress

itertools

marshal

  • Add the allow_code parameter in module functions. Passing allow_code=False prevents serialization and de-serialization of code objects which are incompatible between Python versions. (Contributed by Serhiy Storchaka in gh-113626.)

math

  • A new function fma() for fused multiply-add operations has been added. This function computes x * y + z with only a single round, and so avoids any intermediate loss of precision. It wraps the fma() function provided by C99, and follows the specification of the IEEE 754 “fusedMultiplyAdd” operation for special cases. (Contributed by Mark Dickinson and Victor Stinner in gh-73468.)

mimetypes

mmap

  • The mmap.mmap class now has an seekable() method that can be used when a seekable file-like object is required. The seek() method now returns the new absolute position. (Contributed by Donghee Na and Sylvie Liberman in gh-111835.)

  • mmap.mmap now has a trackfd parameter on Unix; if it is False, the file descriptor specified by fileno will not be duplicated. (Contributed by Zackery Spytz and Petr Viktorin in gh-78502.)

  • mmap.mmap is now protected from crashing on Windows when the mapped memory is inaccessible due to file system errors or access violations. (Contributed by Jannis Weigend in gh-118209.)

opcode

  • Move opcode.ENABLE_SPECIALIZATION to _opcode.ENABLE_SPECIALIZATION. This field was added in 3.12, it was never documented and is not intended for external usage. (Contributed by Irit Katriel in gh-105481.)

  • Removed opcode.is_pseudo, opcode.MIN_PSEUDO_OPCODE and opcode.MAX_PSEUDO_OPCODE, which were added in 3.12, were never documented or exposed through dis, and were not intended to be used externally.

os

os.path

  • Add os.path.isreserved() to check if a path is reserved on the current system. This function is only available on Windows. (Contributed by Barney Gale in gh-88569.)

  • On Windows, os.path.isabs() no longer considers paths starting with exactly one (back)slash to be absolute. (Contributed by Barney Gale and Jon Foster in gh-44626.)

  • Add support of dir_fd and follow_symlinks keyword arguments in shutil.chown(). (Contributed by Berker Peksag and Tahia K in gh-62308)

pathlib

pdb

  • Add ability to move between chained exceptions during post mortem debugging in pm() using the new exceptions [exc_number] command for Pdb. (Contributed by Matthias Bussonnier in gh-106676.)

  • Expressions/statements whose prefix is a pdb command are now correctly identified and executed. (Contributed by Tian Gao in gh-108464.)

  • sys.path[0] will no longer be replaced by the directory of the script being debugged when sys.flags.safe_path is set (via the -P command line option or PYTHONSAFEPATH environment variable). (Contributed by Tian Gao and Christian Walther in gh-111762.)

  • zipapp is supported as a debugging target. (Contributed by Tian Gao in gh-118501.)

  • breakpoint() and pdb.set_trace() now enter the debugger immediately rather than on the next line of code to be executed. This change prevents the debugger from breaking outside of the context when breakpoint() is positioned at the end of the context. (Contributed by Tian Gao in gh-118579.)

queue

random

re

  • Rename re.error to re.PatternError for improved clarity. re.error is kept for backward compatibility.

site

  • .pth files are now decoded by UTF-8 first, and then by the locale encoding if the UTF-8 decoding fails. (Contributed by Inada Naoki in gh-117802.)

sqlite3

statistics

  • Add statistics.kde() for kernel density estimation. This makes it possible to estimate a continuous probability density function from a fixed number of discrete samples. Also added statistics.kde_random() for sampling from the estimated probability density function. (Contributed by Raymond Hettinger in gh-115863.)

subprocess

  • The subprocess module now uses the os.posix_spawn() function in more situations. Notably in the default case of close_fds=True on more recent versions of platforms including Linux, FreeBSD, and Solaris where the C library provides posix_spawn_file_actions_addclosefrom_np(). On Linux this should perform similar to our existing Linux vfork() based code. A private control knob subprocess._USE_POSIX_SPAWN can be set to False if you need to force subprocess not to ever use os.posix_spawn(). Please report your reason and platform details in the CPython issue tracker if you set this so that we can improve our API selection logic for everyone. (Contributed by Jakub Kulik in gh-113117.)

sys

  • Add the sys._is_interned() function to test if the string was interned. This function is not guaranteed to exist in all implementations of Python. (Contributed by Serhiy Storchaka in gh-78573.)

tempfile

time

  • On Windows, time.monotonic() now uses the QueryPerformanceCounter() clock to have a resolution better than 1 us, instead of the GetTickCount64() clock which has a resolution of 15.6 ms. (Contributed by Victor Stinner in gh-88494.)

  • On Windows, time.time() now uses the GetSystemTimePreciseAsFileTime() clock to have a resolution better than 1 μs, instead of the GetSystemTimeAsFileTime() clock which has a resolution of 15.6 ms. (Contributed by Victor Stinner in gh-63207.)

tkinter

  • Add tkinter widget methods: tk_busy_hold(), tk_busy_configure(), tk_busy_cget(), tk_busy_forget(), tk_busy_current(), and tk_busy_status(). (Contributed by Miguel, klappnase and Serhiy Storchaka in gh-72684.)

  • The tkinter widget method wm_attributes() now accepts the attribute name without the minus prefix to get window attributes, e.g. w.wm_attributes('alpha') and allows to specify attributes and values to set as keyword arguments, e.g. w.wm_attributes(alpha=0.5). Add new optional keyword-only parameter return_python_dict: calling w.wm_attributes(return_python_dict=True) returns the attributes as a dict instead of a tuple. (Contributed by Serhiy Storchaka in gh-43457.)

  • Add new optional keyword-only parameter return_ints in the Text.count() method. Passing return_ints=True makes it always returning the single count as an integer instead of a 1-tuple or None. (Contributed by Serhiy Storchaka in gh-97928.)

  • Add support of the “vsapi” element type in the element_create() method of tkinter.ttk.Style. (Contributed by Serhiy Storchaka in gh-68166.)

  • Add the after_info() method for Tkinter widgets. (Contributed by Cheryl Sabella in gh-77020.)

  • Add the PhotoImage method copy_replace() to copy a region from one image to other image, possibly with pixel zooming and/or subsampling. Add from_coords parameter to PhotoImage methods copy(), zoom() and subsample(). Add zoom and subsample parameters to PhotoImage method copy(). (Contributed by Serhiy Storchaka in gh-118225.)

  • Add the PhotoImage methods read() to read an image from a file and data() to get the image data. Add background and grayscale parameters to PhotoImage method write(). (Contributed by Serhiy Storchaka in gh-118271.)

traceback

types

  • SimpleNamespace constructor now allows specifying initial values of attributes as a positional argument which must be a mapping or an iterable of key-value pairs. (Contributed by Serhiy Storchaka in gh-108191.)

typing

unicodedata

  • The Unicode database has been updated to version 15.1.0. (Contributed by James Gerity in gh-109559.)

venv

  • Add support for adding source control management (SCM) ignore files to a virtual environment’s directory. By default, Git is supported. This is implemented as opt-in via the API which can be extended to support other SCMs (venv.EnvBuilder and venv.create()), and opt-out via the CLI (using --without-scm-ignore-files). (Contributed by Brett Cannon in gh-108125.)

warnings

  • The new warnings.deprecated() decorator provides a way to communicate deprecations to static type checkers and to warn on usage of deprecated classes and functions. A runtime deprecation warning may also be emitted when a decorated function or class is used at runtime. See PEP 702. (Contributed by Jelle Zijlstra in gh-104003.)

xml.etree.ElementTree

  • Add the close() method for the iterator returned by iterparse() for explicit cleaning up. (Contributed by Serhiy Storchaka in gh-69893.)

zipimport

  • Gains support for ZIP64 format files. Everybody loves huge code right? (Contributed by Tim Hatch in gh-94146.)

Optimizations

  • textwrap.indent() is now ~30% faster than before for large input. (Contributed by Inada Naoki in gh-107369.)

  • The subprocess module uses os.posix_spawn() in more situations including the default where close_fds=True on many modern platforms. This should provide a noteworthy performance increase launching processes on FreeBSD and Solaris. See the subprocess section above for details. (Contributed by Jakub Kulik in gh-113117.)

  • Several standard library modules have had their import times significantly improved. For example, the import time of the typing module has been reduced by around a third by removing dependencies on re and contextlib. Other modules to enjoy import-time speedups include importlib.metadata, threading, enum, functools and email.utils. (Contributed by Alex Waygood, Shantanu Jain, Adam Turner, Daniel Hollas and others in gh-109653.)

Removed Modules And APIs

PEP 594: dead batteries (and other module removals)

  • PEP 594 removed 19 modules from the standard library, deprecated in Python 3.11:

    • aifc. (Contributed by Victor Stinner in gh-104773.)

    • audioop. (Contributed by Victor Stinner in gh-104773.)

    • chunk. (Contributed by Victor Stinner in gh-104773.)

    • cgi and cgitb.

      • cgi.FieldStorage can typically be replaced with urllib.parse.parse_qsl() for GET and HEAD requests, and the email.message module or multipart PyPI project for POST and PUT.

      • cgi.parse() can be replaced by calling urllib.parse.parse_qs() directly on the desired query string, except for multipart/form-data input, which can be handled as described for cgi.parse_multipart().

      • cgi.parse_header() can be replaced with the functionality in the email package, which implements the same MIME RFCs. For example, with email.message.EmailMessage:

        from email.message import EmailMessage
msg = EmailMessage()
msg['content-type'] = 'application/json; charset="utf8"'
main, params = msg.get_content_type(), msg['content-type'].params

      • cgi.parse_multipart() can be replaced with the functionality in the email package (e.g. email.message.EmailMessage and email.message.Message) which implements the same MIME RFCs, or with the multipart PyPI project.

      (Contributed by Victor Stinner in gh-104773.)

    • crypt module and its private _crypt extension. The hashlib module is a potential replacement for certain use cases. Otherwise, the following PyPI projects can be used:

      • bcrypt: Modern password hashing for your software and your servers.

      • passlib: Comprehensive password hashing framework supporting over 30 schemes.

      • argon2-cffi: The secure Argon2 password hashing algorithm.

      • legacycrypt: ctypes wrapper to the POSIX crypt library call and associated functionality.

      • crypt_r: Fork of the crypt module, wrapper to the crypt_r(3) library call and associated functionality.

      (Contributed by Victor Stinner in gh-104773.)

    • imghdr: use the projects filetype, puremagic, or python-magic instead. (Contributed by Victor Stinner in gh-104773.)

    • mailcap. The mimetypes module provides an alternative. (Contributed by Victor Stinner in gh-104773.)

    • msilib. (Contributed by Zachary Ware in gh-104773.)

    • nis. (Contributed by Victor Stinner in gh-104773.)

    • nntplib: the nntplib PyPI project can be used instead. (Contributed by Victor Stinner in gh-104773.)

    • ossaudiodev: use the pygame project for audio playback. (Contributed by Victor Stinner in gh-104780.)

    • pipes: use the subprocess module instead. (Contributed by Victor Stinner in gh-104773.)

    • sndhdr: use the projects filetype, puremagic, or python-magic instead. (Contributed by Victor Stinner in gh-104773.)

    • spwd: the python-pam project can be used instead. (Contributed by Victor Stinner in gh-104773.)

    • sunau. (Contributed by Victor Stinner in gh-104773.)

    • telnetlib, use the projects telnetlib3 or Exscript instead. (Contributed by Victor Stinner in gh-104773.)

    • uu: the base64 module is a modern alternative. (Contributed by Victor Stinner in gh-104773.)

    • xdrlib. (Contributed by Victor Stinner in gh-104773.)

  • Remove the 2to3 program and the lib2to3 module, deprecated in Python 3.11. (Contributed by Victor Stinner in gh-104780.)

  • Remove the tkinter.tix module, deprecated in Python 3.6. The third-party Tix library which the module wrapped is unmaintained. (Contributed by Zachary Ware in gh-75552.)

configparser

  • Remove the undocumented configparser.LegacyInterpolation class, deprecated in the docstring since Python 3.2, and with a deprecation warning since Python 3.11. (Contributed by Hugo van Kemenade in gh-104886.)

importlib

  • Remove deprecated __getitem__() access for importlib.metadata.EntryPoint objects. (Contributed by Jason R. Coombs in gh-113175.)

locale

  • Remove locale.resetlocale() function deprecated in Python 3.11: use locale.setlocale(locale.LC_ALL, "") instead. (Contributed by Victor Stinner in gh-104783.)

logging

  • logging: Remove undocumented and untested Logger.warn() and LoggerAdapter.warn() methods and logging.warn() function. Deprecated since Python 3.3, they were aliases to the logging.Logger.warning() method, logging.LoggerAdapter.warning() method and logging.warning() function. (Contributed by Victor Stinner in gh-105376.)

pathlib

  • Remove support for using pathlib.Path objects as context managers. This functionality was deprecated and made a no-op in Python 3.9.

re

  • Remove undocumented, never working, and deprecated re.template function and re.TEMPLATE flag (and re.T alias). (Contributed by Serhiy Storchaka and Nikita Sobolev in gh-105687.)

turtle

  • Remove the turtle.RawTurtle.settiltangle() method, deprecated in docs since Python 3.1 and with a deprecation warning since Python 3.11. (Contributed by Hugo van Kemenade in gh-104876.)

typing

  • Namespaces typing.io and typing.re, deprecated in Python 3.8, are now removed. The items in those namespaces can be imported directly from typing. (Contributed by Sebastian Rittau in gh-92871.)

  • Remove support for the keyword-argument method of creating typing.TypedDict types, deprecated in Python 3.11. (Contributed by Tomas Roun in gh-104786.)

unittest

urllib

webbrowser

  • Remove the untested and undocumented webbrowser MacOSX class, deprecated in Python 3.11. Use the MacOSXOSAScript class (introduced in Python 3.2) instead. (Contributed by Hugo van Kemenade in gh-104804.)

  • Remove deprecated webbrowser.MacOSXOSAScript._name attribute. Use webbrowser.MacOSXOSAScript.name attribute instead. (Contributed by Nikita Sobolev in gh-105546.)

New Deprecations

  • Removed chained classmethod descriptors (introduced in gh-63272). This can no longer be used to wrap other descriptors such as property. The core design of this feature was flawed and caused a number of downstream problems. To “pass-through” a classmethod, consider using the __wrapped__ attribute that was added in Python 3.10. (Contributed by Raymond Hettinger in gh-89519.)

  • array: array’s 'u' format code, deprecated in docs since Python 3.3, emits DeprecationWarning since 3.13 and will be removed in Python 3.16. Use the 'w' format code instead. (Contributed by Hugo van Kemenade in gh-80480.)

  • ctypes: Deprecate undocumented ctypes.SetPointerType() and ctypes.ARRAY() functions. Replace ctypes.ARRAY(item_type, size) with item_type * size. (Contributed by Victor Stinner in gh-105733.)

  • decimal: Deprecate non-standard format specifier “N” for decimal.Decimal. It was not documented and only supported in the C implementation. (Contributed by Serhiy Storchaka in gh-89902.)

  • dis: The dis.HAVE_ARGUMENT separator is deprecated. Check membership in hasarg instead. (Contributed by Irit Katriel in gh-109319.)

  • Frame objects: Calling frame.clear() on a suspended frame raises RuntimeError (as has always been the case for an executing frame). (Contributed by Irit Katriel in gh-79932.)

  • getopt and optparse modules: They are now soft deprecated: the argparse module should be used for new projects. Previously, the optparse module was already deprecated, its removal was not scheduled, and no warnings was emitted: so there is no change in practice. (Contributed by Victor Stinner in gh-106535.)

  • gettext: Emit deprecation warning for non-integer numbers in gettext functions and methods that consider plural forms even if the translation was not found. (Contributed by Serhiy Storchaka in gh-88434.)

  • glob: The undocumented glob.glob0() and glob.glob1() functions are deprecated. Use glob.glob() and pass a directory to its root_dir argument instead. (Contributed by Barney Gale in gh-117337.)

  • http.server: http.server.CGIHTTPRequestHandler now emits a DeprecationWarning as it will be removed in 3.15. Process-based CGI HTTP servers have been out of favor for a very long time. This code was outdated, unmaintained, and rarely used. It has a high potential for both security and functionality bugs. This includes removal of the --cgi flag to the python -m http.server command line in 3.15.

  • mimetypes: Passing file path instead of URL in guess_type() is soft deprecated. Use guess_file_type() instead. (Contributed by Serhiy Storchaka in gh-66543.)

  • re: Passing optional arguments maxsplit, count and flags in module-level functions re.split(), re.sub() and re.subn() as positional arguments is now deprecated. In future Python versions these parameters will be keyword-only. (Contributed by Serhiy Storchaka in gh-56166.)

  • pathlib: pathlib.PurePath.is_reserved() is deprecated and scheduled for removal in Python 3.15. Use os.path.isreserved() to detect reserved paths on Windows.

  • platform: java_ver() is deprecated and will be removed in 3.15. It was largely untested, had a confusing API, and was only useful for Jython support. (Contributed by Nikita Sobolev in gh-116349.)

  • pydoc: Deprecate undocumented pydoc.ispackage() function. (Contributed by Zackery Spytz in gh-64020.)

  • sqlite3: Passing more than one positional argument to sqlite3.connect() and the sqlite3.Connection constructor is deprecated. The remaining parameters will become keyword-only in Python 3.15.

    Deprecate passing name, number of arguments, and the callable as keyword arguments for the following sqlite3.Connection APIs:

    Deprecate passing the callback callable by keyword for the following sqlite3.Connection APIs:

    The affected parameters will become positional-only in Python 3.15.

    (Contributed by Erlend E. Aasland in gh-107948 and gh-108278.)

  • sys: sys._enablelegacywindowsfsencoding() function. Replace it with the PYTHONLEGACYWINDOWSFSENCODING environment variable. (Contributed by Inada Naoki in gh-73427.)

  • tarfile: The undocumented and unused tarfile attribute of tarfile.TarFile is deprecated and scheduled for removal in Python 3.16.

  • traceback: The field exc_type of traceback.TracebackException is deprecated. Use exc_type_str instead.

  • typing:

    • Creating a typing.NamedTuple class using keyword arguments to denote the fields (NT = NamedTuple("NT", x=int, y=int)) is deprecated, and will be disallowed in Python 3.15. Use the class-based syntax or the functional syntax instead. (Contributed by Alex Waygood in gh-105566.)

    • When using the functional syntax to create a typing.NamedTuple class or a typing.TypedDict class, failing to pass a value to the ‘fields’ parameter (NT = NamedTuple("NT") or TD = TypedDict("TD")) is deprecated. Passing None to the ‘fields’ parameter (NT = NamedTuple("NT", None) or TD = TypedDict("TD", None)) is also deprecated. Both will be disallowed in Python 3.15. To create a NamedTuple class with 0 fields, use class NT(NamedTuple): pass or NT = NamedTuple("NT", []). To create a TypedDict class with 0 fields, use class TD(TypedDict): pass or TD = TypedDict("TD", {}). (Contributed by Alex Waygood in gh-105566 and gh-105570.)

    • typing.no_type_check_decorator() is deprecated, and scheduled for removal in Python 3.15. After eight years in the typing module, it has yet to be supported by any major type checkers. (Contributed by Alex Waygood in gh-106309.)

    • typing.AnyStr is deprecated. In Python 3.16, it will be removed from typing.__all__, and a DeprecationWarning will be emitted when it is imported or accessed. It will be removed entirely in Python 3.18. Use the new type parameter syntax instead. (Contributed by Michael The in gh-107116.)

  • User-defined functions: Assignment to a function’s __code__ attribute where the new code object’s type does not match the function’s type, is deprecated. The different types are: plain function, generator, async generator and coroutine. (Contributed by Irit Katriel in gh-81137.)

  • wave: Deprecate the getmark(), setmark() and getmarkers() methods of the wave.Wave_read and wave.Wave_write classes. They will be removed in Python 3.15. (Contributed by Victor Stinner in gh-105096.)

Pending Removal in Python 3.14

Pending Removal in Python 3.15

  • http.server.CGIHTTPRequestHandler will be removed along with its related --cgi flag to python -m http.server. It was obsolete and rarely used. No direct replacement exists. Anything is better than CGI to interface a web server with a request handler.

  • locale: locale.getdefaultlocale() was deprecated in Python 3.11 and originally planned for removal in Python 3.13 (gh-90817), but removal has been postponed to Python 3.15. Use locale.setlocale(), locale.getencoding() and locale.getlocale() instead. (Contributed by Hugo van Kemenade in gh-111187.)

  • pathlib: pathlib.PurePath.is_reserved() is deprecated and scheduled for removal in Python 3.15. Use os.path.isreserved() to detect reserved paths on Windows.

  • platform: java_ver() is deprecated and will be removed in 3.15. It was largely untested, had a confusing API, and was only useful for Jython support. (Contributed by Nikita Sobolev in gh-116349.)

  • threading: Passing any arguments to threading.RLock() is now deprecated. C version allows any numbers of args and kwargs, but they are just ignored. Python version does not allow any arguments. All arguments will be removed from threading.RLock() in Python 3.15. (Contributed by Nikita Sobolev in gh-102029.)

  • typing.NamedTuple:

    • The undocumented keyword argument syntax for creating NamedTuple classes (NT = NamedTuple("NT", x=int)) is deprecated, and will be disallowed in 3.15. Use the class-based syntax or the functional syntax instead.

    • When using the functional syntax to create a NamedTuple class, failing to pass a value to the fields parameter (NT = NamedTuple("NT")) is deprecated. Passing None to the fields parameter (NT = NamedTuple("NT", None)) is also deprecated. Both will be disallowed in Python 3.15. To create a NamedTuple class with 0 fields, use class NT(NamedTuple): pass or NT = NamedTuple("NT", []).

  • typing.TypedDict: When using the functional syntax to create a TypedDict class, failing to pass a value to the fields parameter (TD = TypedDict("TD")) is deprecated. Passing None to the fields parameter (TD = TypedDict("TD", None)) is also deprecated. Both will be disallowed in Python 3.15. To create a TypedDict class with 0 fields, use class TD(TypedDict): pass or TD = TypedDict("TD", {}).

  • wave: Deprecate the getmark(), setmark() and getmarkers() methods of the wave.Wave_read and wave.Wave_write classes. They will be removed in Python 3.15. (Contributed by Victor Stinner in gh-105096.)

Pending Removal in Python 3.16

  • array.array 'u' type (wchar_t): use the 'w' type instead (Py_UCS4).

Pending Removal in Future Versions

The following APIs were deprecated in earlier Python versions and will be removed, although there is currently no date scheduled for their removal.

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

  • builtins:

    • ~bool, bitwise inversion on bool.

    • 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.

  • 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.

  • 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.

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

CPython Bytecode Changes

  • The oparg of YIELD_VALUE is now 1 if the yield is part of a yield-from or await, and 0 otherwise. The oparg of RESUME was changed to add a bit indicating whether the except-depth is 1, which is needed to optimize closing of generators. (Contributed by Irit Katriel in gh-111354.)

C API Changes

New Features

Build Changes

  • The configure option --with-system-libmpdec now defaults to yes. The bundled copy of libmpdecimal will be removed in Python 3.15.

  • Autoconf 2.71 and aclocal 1.16.4 are now required to regenerate the configure script. (Contributed by Christian Heimes in gh-89886.)

  • SQLite 3.15.2 or newer is required to build the sqlite3 extension module. (Contributed by Erlend Aasland in gh-105875.)

  • Python built with configure --with-trace-refs (tracing references) is now ABI compatible with the Python release build and debug build. (Contributed by Victor Stinner in gh-108634.)

  • Building CPython now requires a compiler with support for the C11 atomic library, GCC built-in atomic functions, or MSVC interlocked intrinsics.

  • The errno, fcntl, grp, md5, pwd, resource, termios, winsound, _ctypes_test, _multiprocessing.posixshmem, _scproxy, _stat, _statistics, _testconsole, _testimportmultiple and _uuid C extensions are now built with the limited C API. (Contributed by Victor Stinner in gh-85283.)

  • wasm32-wasi is now a PEP 11 tier 2 platform. (Contributed by Brett Cannon in gh-115192.)

  • wasm32-emscripten is no longer a PEP 11 supported platform. (Contributed by Brett Cannon in gh-115192.)

  • Python now bundles the mimalloc library. It is licensed under the MIT license; see mimalloc license. The bundled mimalloc has custom changes, see gh-113141 for details. (Contributed by Dino Viehland in gh-109914.)

  • On POSIX systems, the pkg-config (.pc) filenames now include the ABI flags. For example, the free-threaded build generates python-3.13t.pc and the debug build generates python-3.13d.pc.

Porting to Python 3.13

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

Changes in the Python API

  • An OSError is now raised by getpass.getuser() for any failure to retrieve a username, instead of ImportError on non-Unix platforms or KeyError on Unix platforms where the password database is empty.

  • The threading module now expects the _thread module to have an _is_main_interpreter attribute. It is a function with no arguments that returns True if the current interpreter is the main interpreter.

    Any library or application that provides a custom _thread module must provide _is_main_interpreter(), just like the module’s other “private” attributes. (See gh-112826.)

  • mailbox.Maildir now ignores files with a leading dot. (Contributed by Zackery Spytz in gh-65559.)

  • pathlib.Path.glob() and rglob() now return both files and directories if a pattern that ends with “**” is given, rather than directories only. Users may add a trailing slash to match only directories.

  • The value of the mode attribute of gzip.GzipFile was changed from integer (1 or 2) to string ('rb' or 'wb'). The value of the mode attribute of the readable file-like object returned by zipfile.ZipFile.open() was changed from 'r' to 'rb'. (Contributed by Serhiy Storchaka in gh-115961.)

  • Calling locals() in an optimized scope now produces an independent snapshot on each call, and hence no longer implicitly updates previously returned references. Obtaining the legacy CPython behaviour now requires explicit calls to update the initially returned dictionary with the results of subsequent calls to locals(). Code execution functions that implicitly target locals() (such as exec and eval) must be passed an explicit namespace to access their results in an optimized scope. (Changed as part of PEP 667.)

  • Calling locals() from a comprehension at module or class scope (including via exec or eval) once more behaves as if the comprehension were running as an independent nested function (i.e. the local variables from the containing scope are not included). In Python 3.12, this had changed to include the local variables from the containing scope when implementing PEP 709. (Changed as part of PEP 667.)

  • Accessing FrameType.f_locals in an optimized scope now returns a write-through proxy rather than a snapshot that gets updated at ill-specified times. If a snapshot is desired, it must be created explicitly with dict or the proxy’s .copy() method. (Changed as part of PEP 667.)

Changes in the C API

  • Python.h no longer includes the <ieeefp.h> standard header. It was included for the finite() function which is now provided by the <math.h> header. It should now be included explicitly if needed. Remove also the HAVE_IEEEFP_H macro. (Contributed by Victor Stinner in gh-108765.)

  • Python.h no longer includes these standard header files: <time.h>, <sys/select.h> and <sys/time.h>. If needed, they should now be included explicitly. For example, <time.h> provides the clock() and gmtime() functions, <sys/select.h> provides the select() function, and <sys/time.h> provides the futimes(), gettimeofday() and setitimer() functions. (Contributed by Victor Stinner in gh-108765.)

  • On Windows, Python.h no longer includes the <stddef.h> standard header file. If needed, it should now be included explicitly. For example, it provides offsetof() function, and size_t and ptrdiff_t types. Including <stddef.h> explicitly was already needed by all other platforms, the HAVE_STDDEF_H macro is only defined on Windows. (Contributed by Victor Stinner in gh-108765.)

  • If the Py_LIMITED_API macro is defined, Py_BUILD_CORE, Py_BUILD_CORE_BUILTIN and Py_BUILD_CORE_MODULE macros are now undefined by <Python.h>. (Contributed by Victor Stinner in gh-85283.)

  • The old trashcan macros Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_END were removed. They should be replaced by the new macros Py_TRASHCAN_BEGIN and Py_TRASHCAN_END.

    A tp_dealloc function that has the old macros, such as:

    static void
mytype_dealloc(mytype *p)
{
    PyObject_GC_UnTrack(p);
    Py_TRASHCAN_SAFE_BEGIN(p);
    ...
    Py_TRASHCAN_SAFE_END
}

    should migrate to the new macros as follows:

    static void
mytype_dealloc(mytype *p)
{
    PyObject_GC_UnTrack(p);
    Py_TRASHCAN_BEGIN(p, mytype_dealloc)
    ...
    Py_TRASHCAN_END
}

    Note that Py_TRASHCAN_BEGIN has a second argument which should be the deallocation function it is in. The new macros were added in Python 3.8 and the old macros were deprecated in Python 3.11. (Contributed by Irit Katriel in gh-105111.)

  • Functions PyDict_GetItem(), PyDict_GetItemString(), PyMapping_HasKey(), PyMapping_HasKeyString(), PyObject_HasAttr(), PyObject_HasAttrString(), and PySys_GetObject(), which clear all errors which occurred when calling them, now report them using sys.unraisablehook(). You may replace them with other functions as recommended in the documentation. (Contributed by Serhiy Storchaka in gh-106672.)

  • PyCode_GetFirstFree() is an unstable API now and has been renamed to PyUnstable_Code_GetFirstFree(). (Contributed by Bogdan Romanyuk in gh-115781.)

  • The effects of mutating the dictionary returned from PyEval_GetLocals() in an optimized scope have changed. New dict entries added this way will now only be visible to subsequent PyEval_GetLocals() calls in that frame, as PyFrame_GetLocals(), locals(), and FrameType.f_locals no longer access the same underlying cached dictionary. Changes made to entries for actual variable names and names added via the write-through proxy interfaces will be overwritten on subsequent calls to PyEval_GetLocals() in that frame. The recommended code update depends on how the function was being used, so refer to the deprecation notice on the function for details. (Changed as part of PEP 667.)

  • Calling PyFrame_GetLocals() in an optimized scope now returns a write-through proxy rather than a snapshot that gets updated at ill-specified times. If a snapshot is desired, it must be created explicitly (e.g. with PyDict_Copy()) or by calling the new PyEval_GetFrameLocals() API. (Changed as part of PEP 667.)

  • PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError() no longer have any effect. Calling these functions has been redundant since Python 3.11, when PyFrame_GetLocals() was first introduced. (Changed as part of PEP 667.)

  • PyFrame_LocalsToFast() no longer has any effect. Calling this function is redundant now that PyFrame_GetLocals() returns a write-through proxy for optimized scopes. (Changed as part of PEP 667.)

Removed C APIs

Deprecated C APIs

Pending Removal in Python 3.14

Pending Removal in Python 3.15

Pending Removal in Future Versions

The following APIs were deprecated in earlier Python versions and will be removed, although there is currently no date scheduled for their removal.

Regression Test Changes

  • Python built with configure --with-pydebug now supports a -X presite=package.module command-line option. If used, it specifies a module that should be imported early in the lifecycle of the interpreter, before site.py is executed. (Contributed by Łukasz Langa in gh-110769.)