Editors:

Adam Turner and Hugo van Kemenade

This article explains the new features in Python 3.14, compared to 3.13. Python 3.14 was released on 7 October 2025. For full details, see the changelog.

See also

PEP 745 – Python 3.14 release schedule

Summary – Release highlights

Python 3.14 is the latest stable release of the Python programming language, with a mix of changes to the language, the implementation, and the standard library. The biggest changes include template string literals, deferred evaluation of annotations, and support for subinterpreters in the standard library.

The library changes include significantly improved capabilities for introspection in asyncio, support for Zstandard via a new compression.zstd module, syntax highlighting in the REPL, as well as the usual deprecations and removals, and improvements in user-friendliness and correctness.

This article doesn’t attempt to provide a complete specification of all new features, but instead gives a convenient overview. For full details refer to the documentation, such as the Library Reference and Language Reference. To understand the complete implementation and design rationale for a change, refer to the PEP for a particular new feature; but note that PEPs usually are not kept up-to-date once a feature has been fully implemented. See Porting to Python 3.14 for guidance on upgrading from earlier versions of Python.

Interpreter improvements:

Significant improvements in the standard library:

C API improvements:

Platform support:

Release changes:

New features

PEP 649 & PEP 749: Deferred evaluation of annotations

The annotations on functions, classes, and modules are no longer evaluated eagerly. Instead, annotations are stored in special-purpose annotate functions and evaluated only when necessary (except if from __future__ import annotations is used).

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

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

This example shows how these formats behave:

>>> from annotationlib import get_annotations, Format >>> def func(arg: Undefined): ... pass >>> get_annotations(func, format=Format.VALUE) Traceback (most recent call last): ... NameError: name 'Undefined' is not defined >>> get_annotations(func, format=Format.FORWARDREF) {'arg': ForwardRef('Undefined', owner=<function func at 0x...>)} >>> get_annotations(func, format=Format.STRING) {'arg': 'Undefined'}

The porting section contains guidance on changes that may be needed due to these changes, though in the majority of cases, code will continue working as-is.

(Contributed by Jelle Zijlstra in PEP 749 and gh-119180; PEP 649 was written by Larry Hastings.)

See also

PEP 649

Deferred Evaluation Of Annotations Using Descriptors

PEP 749

Implementing PEP 649

PEP 734: Multiple interpreters in the standard library

The CPython runtime supports running multiple copies of Python in the same process simultaneously and has done so for over 20 years. Each of these separate copies is called an ‘interpreter’. However, the feature had been available only through the C-API.

That limitation is removed in Python 3.14, with the new concurrent.interpreters module.

There are at least two notable reasons why using multiple interpreters has significant benefits:

  • they support a new (to Python), human-friendly concurrency model

  • true multi-core parallelism

For some use cases, concurrency in software improves efficiency and can simplify design, at a high level. At the same time, implementing and maintaining all but the simplest concurrency is often a struggle for the human brain. That especially applies to plain threads (for example, threading), where all memory is shared between all threads.

With multiple isolated interpreters, you can take advantage of a class of concurrency models, like Communicating Sequential Processes (CSP) or the actor model, that have found success in other programming languages, like Smalltalk, Erlang, Haskell, and Go. Think of multiple interpreters as threads but with opt-in sharing.

Regarding multi-core parallelism: as of Python 3.12, interpreters are now sufficiently isolated from one another to be used in parallel (see PEP 684). This unlocks a variety of CPU-intensive use cases for Python that were limited by the GIL.

Using multiple interpreters is similar in many ways to multiprocessing, in that they both provide isolated logical “processes” that can run in parallel, with no sharing by default. However, when using multiple interpreters, an application will use fewer system resources and will operate more efficiently (since it stays within the same process). Think of multiple interpreters as having the isolation of processes with the efficiency of threads.

While the feature has been around for decades, multiple interpreters have not been used widely, due to low awareness and the lack of a standard library module. Consequently, they currently have several notable limitations, which are expected to improve significantly now that the feature is going mainstream.

Current limitations:

  • starting each interpreter has not been optimized yet

  • each interpreter uses more memory than necessary (work continues on extensive internal sharing between interpreters)

  • there aren’t many options yet for truly sharing objects or other data between interpreters (other than memoryview)

  • many third-party extension modules on PyPI are not yet compatible with multiple interpreters (all standard library extension modules are compatible)

  • the approach to writing applications that use multiple isolated interpreters is mostly unfamiliar to Python users, for now

The impact of these limitations will depend on future CPython improvements, how interpreters are used, and what the community solves through PyPI packages. Depending on the use case, the limitations may not have much impact, so try it out!

Furthermore, future CPython releases will reduce or eliminate overhead and provide utilities that are less appropriate on PyPI. In the meantime, most of the limitations can also be addressed through extension modules, meaning PyPI packages can fill any gap for 3.14, and even back to 3.12 where interpreters were finally properly isolated and stopped sharing the GIL. Likewise, libraries on PyPI are expected to emerge for high-level abstractions on top of interpreters.

Regarding extension modules, work is in progress to update some PyPI projects, as well as tools like Cython, pybind11, nanobind, and PyO3. The steps for isolating an extension module are found at Isolating Extension Modules. Isolating a module has a lot of overlap with what is required to support free-threading, so the ongoing work in the community in that area will help accelerate support for multiple interpreters.

Also added in 3.14: concurrent.futures.InterpreterPoolExecutor.

(Contributed by Eric Snow in gh-134939.)

PEP 750: Template string literals

Template strings are a new mechanism for custom string processing. They share the familiar syntax of f-strings but, unlike f-strings, return an object representing the static and interpolated parts of the string, instead of a simple str.

To write a t-string, use a 't' prefix instead of an 'f':

>>> variety = 'Stilton' >>> template = t'Try some {variety} cheese!' >>> type(template) <class 'string.templatelib.Template'>

Template objects provide access to the static and interpolated (in curly braces) parts of a string before they are combined. Iterate over Template instances to access their parts in order:

>>> list(template) ['Try some ', Interpolation('Stilton', 'variety', None, ''), ' cheese!']

It’s easy to write (or call) code to process Template instances. For example, here’s a function that renders static parts lowercase and Interpolation instances uppercase:

from string.templatelib import Interpolation def lower_upper(template): """Render static parts lowercase and interpolations uppercase.""" parts = [] for part in template: if isinstance(part, Interpolation): parts.append(str(part.value).upper()) else: parts.append(part.lower()) return ''.join(parts) name = 'Wenslydale' template = t'Mister {name}' assert lower_upper(template) == 'mister WENSLYDALE'

Because Template instances distinguish between static strings and interpolations at runtime, they can be useful for sanitising user input. Writing a html() function that escapes user input in HTML is an exercise left to the reader! Template processing code can provide improved flexibility. For instance, a more advanced html() function could accept a dict of HTML attributes directly in the template:

attributes = {'src': 'limburger.jpg', 'alt': 'lovely cheese'} template = t'<img {attributes}>' assert html(template) == '<img src="limburger.jpg" alt="lovely cheese" />'

Of course, template processing code does not need to return a string-like result. An even more advanced html() could return a custom type representing a DOM-like structure.

With t-strings in place, developers can write systems that sanitise SQL, make safe shell operations, improve logging, tackle modern ideas in web development (HTML, CSS, and so on), and implement lightweight custom business DSLs.

(Contributed by Jim Baker, Guido van Rossum, Paul Everitt, Koudai Aono, Lysandros Nikolaou, Dave Peck, Adam Turner, Jelle Zijlstra, Bénédikt Tran, and Pablo Galindo Salgado in gh-132661.)

PEP 768: Safe external debugger interface

Python 3.14 introduces a zero-overhead debugging interface that allows debuggers and profilers to safely attach to running Python processes without stopping or restarting them. This is a significant enhancement to Python’s debugging capabilities, meaning that unsafe alternatives are no longer required.

The new interface provides safe execution points for attaching debugger code without modifying the interpreter’s normal execution path or adding any overhead at runtime. Due to this, tools can now inspect and interact with Python applications in real-time, which is a crucial capability for high-availability systems and production environments.

For convenience, this interface is implemented in the sys.remote_exec() function. For example:

import sys from tempfile import NamedTemporaryFile with NamedTemporaryFile(mode='w', suffix='.py', delete=False) as f: script_path = f.name f.write(f'import my_debugger; my_debugger.connect({os.getpid()})') # Execute in process with PID 1234 print('Behold! An offering:') sys.remote_exec(1234, script_path)

This function allows sending Python code to be executed in a target process at the next safe execution point. However, tool authors can also implement the protocol directly as described in the PEP, which details the underlying mechanisms used to safely attach to running processes.

The debugging interface has been carefully designed with security in mind and includes several mechanisms to control access:

(Contributed by Pablo Galindo Salgado, Matt Wozniski, and Ivona Stojanovic in gh-131591.)

A new type of interpreter

A new type of interpreter has been added to CPython. It uses tail calls between small C functions that implement individual Python opcodes, rather than one large C case statement. For certain newer compilers, this interpreter provides significantly better performance. Preliminary benchmarks suggest a geometric mean of 3-5% faster on the standard pyperformance benchmark suite, depending on platform and architecture. The baseline is Python 3.14 built with Clang 19, without this new interpreter.

This interpreter currently only works with Clang 19 and newer on x86-64 and AArch64 architectures. However, a future release of GCC is expected to support this as well.

This feature is opt-in for now. Enabling profile-guided optimization is highly recommendeded when using the new interpreter as it is the only configuration that has been tested and validated for improved performance. For further information, see --with-tail-call-interp.

Note

This is not to be confused with tail call optimization of Python functions, which is currently not implemented in CPython.

This new interpreter type is an internal implementation detail of the CPython interpreter. It doesn’t change the visible behavior of Python programs at all. It can improve their performance, but doesn’t change anything else.

(Contributed by Ken Jin in gh-128563, with ideas on how to implement this in CPython by Mark Shannon, Garrett Gu, Haoran Xu, and Josh Haberman.)

Free-threaded mode improvements

CPython’s free-threaded mode (PEP 703), initially added in 3.13, has been significantly improved in Python 3.14. The implementation described in PEP 703 has been finished, including C API changes, and temporary workarounds in the interpreter were replaced with more permanent solutions. The specializing adaptive interpreter (PEP 659) is now enabled in free-threaded mode, which along with many other optimizations greatly improves its performance. The performance penalty on single-threaded code in free-threaded mode is now roughly 5-10%, depending on the platform and C compiler used.

From Python 3.14, when compiling extension modules for the free-threaded build of CPython on Windows, the preprocessor variable Py_GIL_DISABLED now needs to be specified by the build backend, as it will no longer be determined automatically by the C compiler. For a running interpreter, the setting that was used at compile time can be found using sysconfig.get_config_var().

The new -X context_aware_warnings flag controls if concurrent safe warnings control is enabled. The flag defaults to true for the free-threaded build and false for the GIL-enabled build.

A new thread_inherit_context flag has been added, which if enabled means that threads created with threading.Thread start with a copy of the Context() of the caller of start(). Most significantly, this makes the warning filtering context established by catch_warnings be “inherited” by threads (or asyncio tasks) started within that context. It also affects other modules that use context variables, such as the decimal context manager. This flag defaults to true for the free-threaded build and false for the GIL-enabled build.

(Contributed by Sam Gross, Matt Page, Neil Schemenauer, Thomas Wouters, Donghee Na, Kirill Podoprigora, Ken Jin, Itamar Oren, Brett Simmers, Dino Viehland, Nathan Goldbaum, Ralf Gommers, Lysandros Nikolaou, Kumar Aditya, Edgar Margffoy, and many others. Some of these contributors are employed by Meta, which has continued to provide significant engineering resources to support this project.)

Improved error messages

  • The interpreter now provides helpful suggestions when it detects typos in Python keywords. When a word that closely resembles a Python keyword is encountered, the interpreter will suggest the correct keyword in the error message. This feature helps programmers quickly identify and fix common typing mistakes. For example:

    >>> whille True: ... pass Traceback (most recent call last): File "<stdin>", line 1 whille True: ^^^^^^ SyntaxError: invalid syntax. Did you mean 'while'?

    While the feature focuses on the most common cases, some variations of misspellings may still result in regular syntax errors. (Contributed by Pablo Galindo in gh-132449.)

  • elif statements that follow an else block now have a specific error message. (Contributed by Steele Farnsworth in gh-129902.)

    >>> if who == "me": ... print("It's me!") ... else: ... print("It's not me!") ... elif who is None: ... print("Who is it?") File "<stdin>", line 5 elif who is None: ^^^^ SyntaxError: 'elif' block follows an 'else' block

  • If a statement is passed to the Conditional expressions after else, or one of pass, break, or continue is passed before if, then the error message highlights where the expression is required. (Contributed by Sergey Miryanov in gh-129515.)

    >>> x = 1 if True else pass Traceback (most recent call last): File "<string>", line 1 x = 1 if True else pass ^^^^ SyntaxError: expected expression after 'else', but statement is given >>> x = continue if True else break Traceback (most recent call last): File "<string>", line 1 x = continue if True else break ^^^^^^^^ SyntaxError: expected expression before 'if', but statement is given

  • When incorrectly closed strings are detected, the error message suggests that the string may be intended to be part of the string. (Contributed by Pablo Galindo in gh-88535.)

    >>> "The interesting object "The important object" is very important" Traceback (most recent call last): SyntaxError: invalid syntax. Is this intended to be part of the string?

  • When strings have incompatible prefixes, the error now shows which prefixes are incompatible. (Contributed by Nikita Sobolev in gh-133197.)

    >>> ub'abc' File "<python-input-0>", line 1 ub'abc' ^^ SyntaxError: 'u' and 'b' prefixes are incompatible

  • Improved error messages when using as with incompatible targets in:

    • Imports: import ... as ...

    • From imports: from ... import ... as ...

    • Except handlers: except ... as ...

    • Pattern-match cases: case ... as ...

    (Contributed by Nikita Sobolev in gh-123539, gh-123562, and gh-123440.)

  • Improved error message when trying to add an instance of an unhashable type to a dict or set. (Contributed by CF Bolz-Tereick and Victor Stinner in gh-132828.)

    >>> s = set() >>> s.add({'pages': 12, 'grade': 'A'}) Traceback (most recent call last): File "<python-input-1>", line 1, in <module> s.add({'pages': 12, 'grade': 'A'}) ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TypeError: cannot use 'dict' as a set element (unhashable type: 'dict') >>> d = {} >>> l = [1, 2, 3] >>> d[l] = 12 Traceback (most recent call last): File "<python-input-4>", line 1, in <module> d[l] = 12 ~^^^ TypeError: cannot use 'list' as a dict key (unhashable type: 'list')

  • Improved error message when an object supporting the synchronous context manager protocol is entered using async with instead of with, and vice versa for the asynchronous context manager protocol. (Contributed by Bénédikt Tran in gh-128398.)

PEP 784: Zstandard support in the standard library

The new compression package contains modules compression.lzma, compression.bz2, compression.gzip and compression.zlib which re-export the lzma, bz2, gzip and zlib modules respectively. The new import names under compression are the preferred names for importing these compression modules from Python 3.14. However, the existing modules names have not been deprecated. Any deprecation or removal of the existing compression modules will occur no sooner than five years after the release of 3.14.

The new compression.zstd module provides compression and decompression APIs for the Zstandard format via bindings to Meta’s zstd library. Zstandard is a widely adopted, highly efficient, and fast compression format. In addition to the APIs introduced in compression.zstd, support for reading and writing Zstandard compressed archives has been added to the tarfile, zipfile, and shutil modules.

Here’s an example of using the new module to compress some data:

from compression import zstd import math data = str(math.pi).encode() * 20 compressed = zstd.compress(data) ratio = len(compressed) / len(data) print(f"Achieved compression ratio of {ratio}")

As can be seen, the API is similar to the APIs of the lzma and bz2 modules.

(Contributed by Emma Harper Smith, Adam Turner, Gregory P. Smith, Tomas Roun, Victor Stinner, and Rogdham in gh-132983.)

Asyncio introspection capabilities

Added a new command-line interface to inspect running Python processes using asynchronous tasks, available via python -m asyncio ps PID or python -m asyncio pstree PID.

The ps subcommand inspects the given process ID (PID) and displays information about currently running asyncio tasks. It outputs a task table: a flat listing of all tasks, their names, their coroutine stacks, and which tasks are awaiting them.

The pstree subcommand fetches the same information, but instead renders a visual async call tree, showing coroutine relationships in a hierarchical format. This command is particularly useful for debugging long-running or stuck asynchronous programs. It can help developers quickly identify where a program is blocked, what tasks are pending, and how coroutines are chained together.

For example given this code:

import asyncio async def play_track(track): await asyncio.sleep(5) print(f'🎵 Finished: {track}') async def play_album(name, tracks): async with asyncio.TaskGroup() as tg: for track in tracks: tg.create_task(play_track(track), name=track) async def main(): async with asyncio.TaskGroup() as tg: tg.create_task( play_album('Sundowning', ['TNDNBTG', 'Levitate']), name='Sundowning') tg.create_task( play_album('TMBTE', ['DYWTYLM', 'Aqua Regia']), name='TMBTE') if __name__ == '__main__': asyncio.run(main())

Executing the new tool on the running process will yield a table like this:

python -m asyncio ps 12345 tid task id task name coroutine stack awaiter chain awaiter name awaiter id ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ 1935500 0x7fc930c18050 Task-1 TaskGroup._aexit -> TaskGroup.__aexit__ -> main 0x0 1935500 0x7fc930c18230 Sundowning TaskGroup._aexit -> TaskGroup.__aexit__ -> album TaskGroup._aexit -> TaskGroup.__aexit__ -> main Task-1 0x7fc930c18050 1935500 0x7fc93173fa50 TMBTE TaskGroup._aexit -> TaskGroup.__aexit__ -> album TaskGroup._aexit -> TaskGroup.__aexit__ -> main Task-1 0x7fc930c18050 1935500 0x7fc93173fdf0 TNDNBTG sleep -> play TaskGroup._aexit -> TaskGroup.__aexit__ -> album Sundowning 0x7fc930c18230 1935500 0x7fc930d32510 Levitate sleep -> play TaskGroup._aexit -> TaskGroup.__aexit__ -> album Sundowning 0x7fc930c18230 1935500 0x7fc930d32890 DYWTYLM sleep -> play TaskGroup._aexit -> TaskGroup.__aexit__ -> album TMBTE 0x7fc93173fa50 1935500 0x7fc93161ec30 Aqua Regia sleep -> play TaskGroup._aexit -> TaskGroup.__aexit__ -> album TMBTE 0x7fc93173fa50

or a tree like this:

python -m asyncio pstree 12345 └── (T) Task-1 └── main example.py:13 └── TaskGroup.__aexit__ Lib/asyncio/taskgroups.py:72 └── TaskGroup._aexit Lib/asyncio/taskgroups.py:121 ├── (T) Sundowning │ └── album example.py:8 │ └── TaskGroup.__aexit__ Lib/asyncio/taskgroups.py:72 │ └── TaskGroup._aexit Lib/asyncio/taskgroups.py:121 │ ├── (T) TNDNBTG │ │ └── play example.py:4 │ │ └── sleep Lib/asyncio/tasks.py:702 │ └── (T) Levitate │ └── play example.py:4 │ └── sleep Lib/asyncio/tasks.py:702 └── (T) TMBTE └── album example.py:8 └── TaskGroup.__aexit__ Lib/asyncio/taskgroups.py:72 └── TaskGroup._aexit Lib/asyncio/taskgroups.py:121 ├── (T) DYWTYLM │ └── play example.py:4 │ └── sleep Lib/asyncio/tasks.py:702 └── (T) Aqua Regia └── play example.py:4 └── sleep Lib/asyncio/tasks.py:702

If a cycle is detected in the async await graph (which could indicate a programming issue), the tool raises an error and lists the cycle paths that prevent tree construction:

python -m asyncio pstree 12345 ERROR: await-graph contains cycles - cannot print a tree! cycle: Task-2 → Task-3 → Task-2

(Contributed by Pablo Galindo, Łukasz Langa, Yury Selivanov, and Marta Gomez Macias in gh-91048.)

Concurrent safe warnings control

The warnings.catch_warnings context manager will now optionally use a context variable for warning filters. This is enabled by setting the context_aware_warnings flag, either with the -X command-line option or an environment variable. This gives predictable warnings control when using catch_warnings combined with multiple threads or asynchronous tasks. The flag defaults to true for the free-threaded build and false for the GIL-enabled build.

(Contributed by Neil Schemenauer and Kumar Aditya in gh-130010.)

Other language changes

  • All Windows code pages are now supported as ‘cpXXX’ codecs on Windows. (Contributed by Serhiy Storchaka in gh-123803.)

  • Implement mixed-mode arithmetic rules combining real and complex numbers as specified by the C standard since C99. (Contributed by Sergey B Kirpichev in gh-69639.)

  • More syntax errors are now detected regardless of optimisation and the -O command-line option. This includes writes to __debug__, incorrect use of await, and asynchronous comprehensions outside asynchronous functions. For example, python -O -c 'assert (__debug__ := 1)' or python -O -c 'assert await 1' now produce SyntaxErrors. (Contributed by Irit Katriel and Jelle Zijlstra in gh-122245 & gh-121637.)

  • When subclassing a pure C type, the C slots for the new type are no longer replaced with a wrapped version on class creation if they are not explicitly overridden in the subclass. (Contributed by Tomasz Pytel in gh-132284.)

Built-ins

Command line and environment

  • The import time flag can now track modules that are already loaded (‘cached’), via the new -X importtime=2. When such a module is imported, the self and cumulative times are replaced by the string cached.

    Values above 2 for -X importtime are now reserved for future use.

    (Contributed by Noah Kim and Adam Turner in gh-118655.)

  • The command-line option -c now automatically dedents its code argument before execution. The auto-dedentation behavior mirrors textwrap.dedent(). (Contributed by Jon Crall and Steven Sun in gh-103998.)

  • -J is no longer a reserved flag for Jython, and now has no special meaning. (Contributed by Adam Turner in gh-133336.)

PEP 758: Allow except and except* expressions without brackets

The except and except* expressions now allow brackets to be omitted when there are multiple exception types and the as clause is not used. For example:

try: connect_to_server() except TimeoutError, ConnectionRefusedError: print('The network has ceased to be!')

(Contributed by Pablo Galindo and Brett Cannon in PEP 758 and gh-131831.)

PEP 765: Control flow in finally blocks

The compiler now emits a SyntaxWarning when a return, break, or continue statement have the effect of leaving a finally block. This change is specified in PEP 765.

In situations where this change is inconvenient (such as those where the warnings are redundant due to code linting), the warning filter can be used to turn off all syntax warnings by adding ignore::SyntaxWarning as a filter. This can be specified in combination with a filter that converts other warnings to errors (for example, passing -Werror -Wignore::SyntaxWarning as CLI options, or setting PYTHONWARNINGS=error,ignore::SyntaxWarning).

Note that applying such a filter at runtime using the warnings module will only suppress the warning in code that is compiled after the filter is adjusted. Code that is compiled prior to the filter adjustment (for example, when a module is imported) will still emit the syntax warning.

(Contributed by Irit Katriel in gh-130080.)

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.

There are now only two generations: young and old. When gc.collect() is not called directly, the GC is invoked a little less frequently. When invoked, it collects the young generation and an increment of the old generation, instead of collecting one or more generations.

The behavior of gc.collect() changes slightly:

  • gc.collect(1): Performs an increment of garbage collection, rather than collecting generation 1.

  • Other calls to gc.collect() are unchanged.

(Contributed by Mark Shannon in gh-108362.)

Default interactive shell

  • The default interactive shell now highlights Python syntax. The feature is enabled by default, save if PYTHON_BASIC_REPL or any other environment variable that disables colour is set. See Controlling color for details.

    The default color theme for syntax highlighting strives for good contrast and exclusively uses the 4-bit VGA standard ANSI color codes for maximum compatibility. The theme can be customized using an experimental API _colorize.set_theme(). This can be called interactively or in the PYTHONSTARTUP script. Note that this function has no stability guarantees, and may change or be removed.

    (Contributed by Łukasz Langa in gh-131507.)

  • The default interactive shell now supports import auto-completion. This means that typing import co and pressing <Tab> will suggest modules starting with co. Similarly, typing from concurrent import i will suggest submodules of concurrent starting with i. Note that autocompletion of module attributes is not currently supported. (Contributed by Tomas Roun in gh-69605.)

New modules

  • annotationlib: For introspecting annotations. See PEP 749 for more details. (Contributed by Jelle Zijlstra in gh-119180.)

  • compression (including compression.zstd): A package for compression-related modules, including a new module to support the Zstandard compression format. See PEP 784 for more details. (Contributed by Emma Harper Smith, Adam Turner, Gregory P. Smith, Tomas Roun, Victor Stinner, and Rogdham in gh-132983.)

  • concurrent.interpreters: Support for multiple interpreters in the standard library. See PEP 734 for more details. (Contributed by Eric Snow in gh-134939.)

  • string.templatelib: Support for template string literals (t-strings). See PEP 750 for more details. (Contributed by Jim Baker, Guido van Rossum, Paul Everitt, Koudai Aono, Lysandros Nikolaou, Dave Peck, Adam Turner, Jelle Zijlstra, Bénédikt Tran, and Pablo Galindo Salgado in gh-132661.)

Improved modules

argparse

  • The default value of the program name for argparse.ArgumentParser now reflects the way the Python interpreter was instructed to find the __main__ module code. (Contributed by Serhiy Storchaka and Alyssa Coghlan in gh-66436.)

  • Introduced the optional suggest_on_error parameter to argparse.ArgumentParser, enabling suggestions for argument choices and subparser names if mistyped by the user. (Contributed by Savannah Ostrowski in gh-124456.)

  • Enable color for help text, which can be disabled with the optional color parameter to argparse.ArgumentParser. This can also be controlled by environment variables. (Contributed by Hugo van Kemenade in gh-130645.)

ast

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

  • Add support for copy.replace() for AST nodes. (Contributed by Bénédikt Tran in gh-121141.)

  • Docstrings are now removed from an optimized AST in optimization level 2. (Contributed by Irit Katriel in gh-123958.)

  • The repr() output for AST nodes now includes more information. (Contributed by Tomas Roun in gh-116022.)

  • When called with an AST as input, the parse() function now always verifies that the root node type is appropriate. (Contributed by Irit Katriel in gh-130139.)

  • Add new options to the command-line interface: --feature-version, --optimize, and --show-empty. (Contributed by Semyon Moroz in gh-133367.)

asyncio

calendar

concurrent.futures

  • Add a new executor class, InterpreterPoolExecutor, which exposes multiple Python interpreters in the same process (‘subinterpreters’) to Python code. This uses a pool of independent Python interpreters to execute calls asynchronously.

    This is separate from the new interpreters module introduced by PEP 734. (Contributed by Eric Snow in gh-124548.)

  • On Unix platforms other than macOS, ‘forkserver’ is now the the default start method for ProcessPoolExecutor (replacing ‘fork’). This change does not affect Windows or macOS, where ‘spawn’ remains the default start method.

    If the threading incompatible fork method is required, you must explicitly request it by supplying a multiprocessing context mp_context to ProcessPoolExecutor.

    See forkserver restrictions for information and differences with the fork method and how this change may affect existing code with mutable global shared variables and/or shared objects that can not be automatically pickled.

    (Contributed by Gregory P. Smith in gh-84559.)

  • Add two new methods to ProcessPoolExecutor, terminate_workers() and kill_workers(), as ways to terminate or kill all living worker processes in the given pool. (Contributed by Charles Machalow in gh-130849.)

  • Add the optional buffersize parameter to Executor.map to limit the number of submitted tasks whose results have not yet been yielded. If the buffer is full, iteration over the iterables pauses until a result is yielded from the buffer. (Contributed by Enzo Bonnal and Josh Rosenberg in gh-74028.)

configparser

  • configparser will no longer write config files it cannot read, to improve security. Attempting to write() keys containing delimiters or beginning with the section header pattern will raise an InvalidWriteError. (Contributed by Jacob Lincoln in gh-129270.)

contextvars

ctypes

  • The layout of bit fields in Structure and Union objects is now a closer match to platform defaults (GCC/Clang or MSVC). In particular, fields no longer overlap. (Contributed by Matthias Görgens in gh-97702.)

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

  • The class of Structure/Union field descriptors is now available as CField, and has new attributes to aid debugging and introspection. (Contributed by Petr Viktorin in gh-128715.)

  • On Windows, the COMError exception is now public. (Contributed by Jun Komoda in gh-126686.)

  • On Windows, the CopyComPointer() function is now public. (Contributed by Jun Komoda in gh-127275.)

  • Add memoryview_at(), a function to create a memoryview object that refers to the supplied pointer and length. This works like ctypes.string_at() except it avoids a buffer copy, and is typically useful when implementing pure Python callback functions that are passed dynamically-sized buffers. (Contributed by Rian Hunter in gh-112018.)

  • Complex types, c_float_complex, c_double_complex, and c_longdouble_complex, are now available if both the compiler and the libffi library support complex C types. (Contributed by Sergey B Kirpichev in gh-61103.)

  • Add ctypes.util.dllist() for listing the shared libraries loaded by the current process. (Contributed by Brian Ward in gh-119349.)

  • Move ctypes.POINTER() types cache from a global internal cache (_pointer_type_cache) to the _CData.__pointer_type__ attribute of the corresponding ctypes types. This will stop the cache from growing without limits in some situations. (Contributed by Sergey Miryanov in gh-100926.)

  • The py_object type now supports subscription, making it a generic type. (Contributed by Brian Schubert in gh-132168.)

  • ctypes now supports free-threading builds. (Contributed by Kumar Aditya and Peter Bierma in gh-127945.)

curses

datetime

decimal

difflib

  • Comparison pages with highlighted changes generated by the HtmlDiff class now support ‘dark mode’. (Contributed by Jiahao Li in gh-129939.)

dis

errno

faulthandler

fnmatch

  • Add filterfalse(), a function to reject names matching a given pattern. (Contributed by Bénédikt Tran in gh-74598.)

fractions

functools

getopt

  • Add support for options with optional arguments. (Contributed by Serhiy Storchaka in gh-126374.)

  • Add support for returning intermixed options and non-option arguments in order. (Contributed by Serhiy Storchaka in gh-126390.)

getpass

  • Support keyboard feedback in the getpass() function via the keyword-only optional argument echo_char. Placeholder characters are rendered whenever a character is entered, and removed when a character is deleted. (Contributed by Semyon Moroz in gh-77065.)

graphlib

heapq

hmac

  • Add a built-in implementation for HMAC (RFC 2104) using formally verified code from the HACL* project. This implementation is used as a fallback when the OpenSSL implementation of HMAC is not available. (Contributed by Bénédikt Tran in gh-99108.)

http

  • Directory lists and error pages generated by the http.server module allow the browser to apply its default dark mode. (Contributed by Yorik Hansen in gh-123430.)

  • The http.server module now supports serving over HTTPS using the http.server.HTTPSServer class. This functionality is exposed by the command-line interface (python -m http.server) through the following options:

    (Contributed by Semyon Moroz in gh-85162.)

imaplib

inspect

io

json

linecache

  • getline() can now retrieve source code for frozen modules. (Contributed by Tian Gao in gh-131638.)

logging.handlers

math

  • Added more detailed error messages for domain errors in the module. (Contributed by Charlie Zhao and Sergey B Kirpichev in gh-101410.)

mimetypes

  • Add a public command-line for the module, invoked via python -m mimetypes. (Contributed by Oleg Iarygin and Hugo van Kemenade in gh-93096.)

  • Add several new MIME types based on RFCs and common usage:

    Microsoft and RFC 8081 MIME types for fonts

    • Embedded OpenType: application/vnd.ms-fontobject

    • OpenType Layout (OTF) font/otf

    • TrueType: font/ttf

    • WOFF 1.0 font/woff

    • WOFF 2.0 font/woff2

    RFC 9559 MIME types for Matroska audiovisual data container structures

    • audio with no video: audio/matroska (.mka)

    • video: video/matroska (.mkv)

    • stereoscopic video: video/matroska-3d (.mk3d)

    Images with RFCs

    • RFC 1494: CCITT Group 3 (.g3)

    • RFC 3362: Real-time Facsimile, T.38 (.t38)

    • RFC 3745: JPEG 2000 (.jp2), extension (.jpx) and compound (.jpm)

    • RFC 3950: Tag Image File Format Fax eXtended, TIFF-FX (.tfx)

    • RFC 4047: Flexible Image Transport System (.fits)

    • RFC 7903: Enhanced Metafile (.emf) and Windows Metafile (.wmf)

    Other MIME type additions and changes

    • RFC 2361: Change type for .avi to video/vnd.avi and for .wav to audio/vnd.wave

    • RFC 4337: Add MPEG-4 audio/mp4 (.m4a)

    • RFC 5334: Add Ogg media (.oga, .ogg and .ogx)

    • RFC 6713: Add gzip application/gzip (.gz)

    • RFC 9639: Add FLAC audio/flac (.flac)

    • RFC 9512 application/yaml MIME type for YAML files (.yaml and .yml)

    • Add 7z application/x-7z-compressed (.7z)

    • Add Android Package application/vnd.android.package-archive (.apk) when not strict

    • Add deb application/x-debian-package (.deb)

    • Add glTF binary model/gltf-binary (.glb)

    • Add glTF JSON/ASCII model/gltf+json (.gltf)

    • Add M4V video/x-m4v (.m4v)

    • Add PHP application/x-httpd-php (.php)

    • Add RAR application/vnd.rar (.rar)

    • Add RPM application/x-rpm (.rpm)

    • Add STL model/stl (.stl)

    • Add Windows Media Video video/x-ms-wmv (.wmv)

    • De facto: Add WebM audio/webm (.weba)

    • ECMA-376: Add .docx, .pptx and .xlsx types

    • OASIS: Add OpenDocument .odg, .odp, .ods and .odt types

    • W3C: Add EPUB application/epub+zip (.epub)

    (Contributed by Sahil Prajapati and Hugo van Kemenade in gh-84852, by Sasha “Nelie” Chernykh and Hugo van Kemenade in gh-132056, and by Hugo van Kemenade in gh-89416, gh-85957, and gh-129965.)

multiprocessing

  • On Unix platforms other than macOS, ‘forkserver’ is now the the default start method (replacing ‘fork’). This change does not affect Windows or macOS, where ‘spawn’ remains the default start method.

    If the threading incompatible fork method is required, you must explicitly request it via a context from get_context() (preferred) or change the default via set_start_method().

    See forkserver restrictions for information and differences with the fork method and how this change may affect existing code with mutable global shared variables and/or shared objects that can not be automatically pickled.

    (Contributed by Gregory P. Smith in gh-84559.)

  • multiprocessing’s 'forkserver' start method now authenticates its control socket to avoid solely relying on filesystem permissions to restrict what other processes could cause the forkserver to spawn workers and run code. (Contributed by Gregory P. Smith for gh-97514.)

  • The multiprocessing proxy objects for list and dict types gain previously overlooked missing methods:

    • clear() and copy() for proxies of list

    • fromkeys(), reversed(d), d | {}, {} | d, d |= {'b': 2} for proxies of dict

    (Contributed by Roy Hyunjin Han for gh-103134.)

  • Add support for shared set objects via SyncManager.set(). The set() in Manager() method is now available. (Contributed by Mingyu Park in gh-129949.)

  • Add the interrupt() to multiprocessing.Process objects, which terminates the child process by sending SIGINT. This enables finally clauses to print a stack trace for the terminated process. (Contributed by Artem Pulkin in gh-131913.)

operator

  • Add is_none() and is_not_none() as a pair of functions, such that operator.is_none(obj) is equivalent to obj is None and operator.is_not_none(obj) is equivalent to obj is not None. (Contributed by Raymond Hettinger and Nico Mexis in gh-115808.)

os

os.path

pathlib

  • Add methods to pathlib.Path to recursively copy or move files and directories:

    • copy() copies a file or directory tree to a destination.

    • copy_into() copies into a destination directory.

    • move() moves a file or directory tree to a destination.

    • move_into() moves into a destination directory.

    (Contributed by Barney Gale in gh-73991.)

  • Add the info attribute, which stores an object implementing the new pathlib.types.PathInfo protocol. The object supports querying the file type and internally caching stat() results. Path objects generated by iterdir() are initialized with file type information gleaned from scanning the parent directory. (Contributed by Barney Gale in gh-125413.)

pdb

  • The pdb module now supports remote attaching to a running Python process using a new -p PID command-line option:

    This will connect to the Python process with the given PID and allow you to debug it interactively. Notice that due to how the Python interpreter works attaching to a remote process that is blocked in a system call or waiting for I/O will only work once the next bytecode instruction is executed or when the process receives a signal.

    This feature uses PEP 768 and the new sys.remote_exec() function to attach to the remote process and send the PDB commands to it.

    (Contributed by Matt Wozniski and Pablo Galindo in gh-131591.)

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

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

  • A confirmation prompt will be shown when the user tries to quit pdb in inline mode. y, Y, <Enter> or EOF will confirm the quit and call sys.exit(), instead of raising bdb.BdbQuit. (Contributed by Tian Gao in gh-124704.)

  • Inline breakpoints like breakpoint() or pdb.set_trace() will always stop the program at calling frame, ignoring the skip pattern (if any). (Contributed by Tian Gao in gh-130493.)

  • <tab> at the beginning of the line in pdb multi-line input will fill in a 4-space indentation now, instead of inserting a \t character. (Contributed by Tian Gao in gh-130471.)

  • Auto-indent is introduced in pdb multi-line input. It will either keep the indentation of the last line or insert a 4-space indentation when it detects a new code block. (Contributed by Tian Gao in gh-133350.)

  • $_asynctask is added to access the current asyncio task if applicable. (Contributed by Tian Gao in gh-124367.)

  • pdb.set_trace_async() is added to support debugging asyncio coroutines. await statements are supported with this function. (Contributed by Tian Gao in gh-132576.)

  • Source code displayed in pdb will be syntax-highlighted. This feature can be controlled using the same methods as the default interactive shell, in addition to the newly added colorize argument of pdb.Pdb. (Contributed by Tian Gao and Łukasz Langa in gh-133355.)

pickle

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

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

platform

pydoc

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

re

  • Support \z as a synonym for \Z in regular expressions. It is interpreted unambiguously in many other regular expression engines, unlike \Z, which has subtly different behavior. (Contributed by Serhiy Storchaka in gh-133306.)

  • \B in regular expression now matches the empty input string, meaning that it is now always the opposite of \b. (Contributed by Serhiy Storchaka in gh-124130.)

socket

  • Improve and fix support for Bluetooth sockets.

    • Fix support of Bluetooth sockets on NetBSD and DragonFly BSD. (Contributed by Serhiy Storchaka in gh-132429.)

    • Fix support for BTPROTO_HCI on FreeBSD. (Contributed by Victor Stinner in gh-111178.)

    • Add support for BTPROTO_SCO on FreeBSD. (Contributed by Serhiy Storchaka in gh-85302.)

    • Add support for cid and bdaddr_type in the address for BTPROTO_L2CAP on FreeBSD. (Contributed by Serhiy Storchaka in gh-132429.)

    • Add support for channel in the address for BTPROTO_HCI on Linux. (Contributed by Serhiy Storchaka in gh-70145.)

    • Accept an integer as the address for BTPROTO_HCI on Linux. (Contributed by Serhiy Storchaka in gh-132099.)

    • Return cid in getsockname() for BTPROTO_L2CAP. (Contributed by Serhiy Storchaka in gh-132429.)

    • Add many new constants. (Contributed by Serhiy Storchaka in gh-132734.)

ssl

  • Indicate through the HAS_PHA Boolean whether the ssl module supports TLSv1.3 post-handshake client authentication (PHA). (Contributed by Will Childs-Klein in gh-128036.)

struct

  • Support the float complex and double complex C types in the struct module (formatting characters 'F' and 'D' respectively). (Contributed by Sergey B Kirpichev in gh-121249.)

symtable

sys

  • The previously undocumented special function sys.getobjects(), which only exists in specialized builds of Python, may now return objects from other interpreters than the one it’s called in. (Contributed by Eric Snow in gh-125286.)

  • Add sys._is_immortal() for determining if an object is immortal. (Contributed by Peter Bierma in gh-128509.)

  • On FreeBSD, sys.platform no longer contains the major version number. It is always 'freebsd', instead of 'freebsd13' or 'freebsd14'. (Contributed by Michael Osipov in gh-129393.)

  • Raise DeprecationWarning for sys._clear_type_cache(). This function was deprecated in Python 3.13 but it didn’t raise a runtime warning.

  • Add sys.remote_exec() to implement the new external debugger interface. See PEP 768 for details. (Contributed by Pablo Galindo Salgado, Matt Wozniski, and Ivona Stojanovic in gh-131591.)

  • Add the sys._jit namespace, containing utilities for introspecting just-in-time compilation. (Contributed by Brandt Bucher in gh-133231.)

sys.monitoring

sysconfig

tarfile

threading

tkinter

  • Make tkinter widget methods after() and after_idle() accept keyword arguments. (Contributed by Zhikang Yan in gh-126899.)

  • Add ability to specify a name for tkinter.OptionMenu and tkinter.ttk.OptionMenu. (Contributed by Zhikang Yan in gh-130482.)

turtle

types

typing

  • The types.UnionType and typing.Union types are now aliases for each other, meaning that both old-style unions (created with Union[int, str]) and new-style unions (int | str) now create instances of the same runtime type. This unifies the behavior between the two syntaxes, but leads to some differences in behavior that may affect users who introspect types at runtime:

    • Both syntaxes for creating a union now produce the same string representation in repr(). For example, repr(Union[int, str]) is now "int | str" instead of "typing.Union[int, str]".

    • Unions created using the old syntax are no longer cached. Previously, running Union[int, str] multiple times would return the same object (Union[int, str] is Union[int, str] would be True), but now it will return two different objects. Use == to compare unions for equality, not is. New-style unions have never been cached this way. This change could increase memory usage for some programs that use a large number of unions created by subscripting typing.Union. However, several factors offset this cost: unions used in annotations are no longer evaluated by default in Python 3.14 because of PEP 649; an instance of types.UnionType is itself much smaller than the object returned by Union[] was on prior Python versions; and removing the cache also saves some space. It is therefore unlikely that this change will cause a significant increase in memory usage for most users.

    • Previously, old-style unions were implemented using the private class typing._UnionGenericAlias. This class is no longer needed for the implementation, but it has been retained for backward compatibility, with removal scheduled for Python 3.17. Users should use documented introspection helpers like get_origin() and typing.get_args() instead of relying on private implementation details.

    • It is now possible to use typing.Union itself in isinstance() checks. For example, isinstance(int | str, typing.Union) will return True; previously this raised TypeError.

    • The __args__ attribute of typing.Union objects is no longer writable.

    • It is no longer possible to set any attributes on Union objects. This only ever worked for dunder attributes on previous versions, was never documented to work, and was subtly broken in many cases.

    (Contributed by Jelle Zijlstra in gh-105499.)

  • TypeAliasType now supports star unpacking.

unicodedata

  • The Unicode database has been updated to Unicode 16.0.0.

unittest

urllib

  • Upgrade HTTP digest authentication algorithm for urllib.request by supporting SHA-256 digest authentication as specified in RFC 7616. (Contributed by Calvin Bui in gh-128193.)

  • Improve ergonomics and standards compliance when parsing and emitting file: URLs.

    In url2pathname():

    • Accept a complete URL when the new require_scheme argument is set to true.

    • Discard URL authority if it matches the local hostname.

    • Discard URL authority if it resolves to a local IP address when the new resolve_host argument is set to true.

    • Discard URL query and fragment components.

    • Raise URLError if a URL authority isn’t local, except on Windows where we return a UNC path as before.

    In pathname2url():

    • Return a complete URL when the new add_scheme argument is set to true.

    • Include an empty URL authority when a path begins with a slash. For example, the path /etc/hosts is converted to the URL ///etc/hosts.

    On Windows, drive letters are no longer converted to uppercase, and : characters not following a drive letter no longer cause an OSError exception to be raised.

    (Contributed by Barney Gale in gh-125866.)

uuid

webbrowser

  • Names in the BROWSER environment variable can now refer to already registered browsers for the webbrowser module, instead of always generating a new browser command.

    This makes it possible to set BROWSER to the value of one of the supported browsers on macOS.

zipfile

Optimizations

asyncio

  • Standard benchmark results have improved by 10-20% following the implementation of a new per-thread doubly linked list for native tasks, also reducing memory usage. This enables external introspection tools such as python -m asyncio pstree to introspect the call graph of asyncio tasks running in all threads. (Contributed by Kumar Aditya in gh-107803.)

  • The module now has first class support for free-threading builds. This enables parallel execution of multiple event loops across different threads, scaling linearly with the number of threads. (Contributed by Kumar Aditya in gh-128002.)

base64

  • b16decode() is now up to six times faster. (Contributed by Bénédikt Tran, Chris Markiewicz, and Adam Turner in gh-118761.)

bdb

  • The basic debugger now has a sys.monitoring-based backend, which can be selected via the passing 'monitoring' to the Bdb class’s new backend parameter. (Contributed by Tian Gao in gh-124533.)

difflib

  • The IS_LINE_JUNK() function is now up to twice as fast. (Contributed by Adam Turner and Semyon Moroz in gh-130167.)

gc

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

    Because of this optimization, the meaning of the results of get_threshold() and set_threshold() have changed, along with get_count() and get_stats().

    • For backwards compatibility, get_threshold() continues to return a three-item tuple. 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 now meaningless and is always zero.

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

    • get_count() and get_stats() continue to return the same format of results. 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.

    (Contributed by Mark Shannon in gh-108362.)

io

  • Opening and reading files now executes fewer system calls. Reading a small operating system cached file in full is up to 15% faster. (Contributed by Cody Maloney and Victor Stinner in gh-120754 and gh-90102.)

pathlib

  • Path.read_bytes now uses unbuffered mode to open files, which is between 9% and 17% faster to read in full. (Contributed by Cody Maloney in gh-120754.)

pdb

uuid

  • uuid3() and uuid5() are now both roughly 40% faster for 16-byte names and 20% faster for 1024-byte names. Performance for longer names remains unchanged. (Contributed by Bénédikt Tran in gh-128150.)

  • uuid4() is now c. 30% faster. (Contributed by Bénédikt Tran in gh-128150.)

zlib

  • On Windows, zlib-ng is now used as the implementation of the zlib module in the default binaries. There are no known incompatibilities between zlib-ng and the previously-used zlib implementation. This should result in better performance at all compression levels.

    It is worth noting that zlib.Z_BEST_SPEED (1) may result in significantly less compression than the previous implementation, whilst also significantly reducing the time taken to compress.

    (Contributed by Steve Dower in gh-91349.)

Removed

argparse

  • Remove the type, choices, and metavar parameters of BooleanOptionalAction. These have been deprecated since Python 3.12. (Contributed by Nikita Sobolev in gh-118805.)

  • Calling add_argument_group() on an argument group now raises a ValueError. Similarly, add_argument_group() or add_mutually_exclusive_group() on a mutually exclusive group now both raise ValueErrors. This ‘nesting’ was never supported, often failed to work correctly, and was unintentionally exposed through inheritance. This functionality has been deprecated since Python 3.11. (Contributed by Savannah Ostrowski in gh-127186.)

ast

  • Remove the following classes, which have been deprecated aliases of Constant since Python 3.8 and have emitted deprecation warnings since Python 3.12:

    • Bytes

    • Ellipsis

    • NameConstant

    • Num

    • Str

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

    (Contributed by Alex Waygood in gh-119562.)

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

    • Constant.n

    • Constant.s

    Use Constant.value instead. (Contributed by Alex Waygood in gh-119562.)

asyncio

  • Remove the following classes, methods, and functions, which have been deprecated since Python 3.12:

    • AbstractChildWatcher

    • FastChildWatcher

    • MultiLoopChildWatcher

    • PidfdChildWatcher

    • SafeChildWatcher

    • ThreadedChildWatcher

    • AbstractEventLoopPolicy.get_child_watcher()

    • AbstractEventLoopPolicy.set_child_watcher()

    • get_child_watcher()

    • set_child_watcher()

    (Contributed by Kumar Aditya in gh-120804.)

  • asyncio.get_event_loop() now raises a RuntimeError if there is no current event loop, and no longer implicitly creates an event loop.

    (Contributed by Kumar Aditya in gh-126353.)

    There’s a few patterns that use asyncio.get_event_loop(), most of them can be replaced with asyncio.run().

    If you’re running an async function, simply use asyncio.run().

    Before:

    async def main(): ... loop = asyncio.get_event_loop() try: loop.run_until_complete(main()) finally: loop.close()

    After:

    async def main(): ... asyncio.run(main())

    If you need to start something, for example, a server listening on a socket and then run forever, use asyncio.run() and an asyncio.Event.

    Before:

    def start_server(loop): ... loop = asyncio.get_event_loop() try: start_server(loop) loop.run_forever() finally: loop.close()

    After:

    def start_server(loop): ... async def main(): start_server(asyncio.get_running_loop()) await asyncio.Event().wait() asyncio.run(main())

    If you need to run something in an event loop, then run some blocking code around it, use asyncio.Runner.

    Before:

    async def operation_one(): ... def blocking_code(): ... async def operation_two(): ... loop = asyncio.get_event_loop() try: loop.run_until_complete(operation_one()) blocking_code() loop.run_until_complete(operation_two()) finally: loop.close()

    After:

    async def operation_one(): ... def blocking_code(): ... async def operation_two(): ... with asyncio.Runner() as runner: runner.run(operation_one()) blocking_code() runner.run(operation_two())

email

  • Remove email.utils.localtime()’s isdst parameter, which was deprecated in and has been ignored since Python 3.12. (Contributed by Hugo van Kemenade in gh-118798.)

importlib.abc

itertools

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

pathlib

  • Remove support for passing additional keyword arguments to Path. In previous versions, any such arguments are ignored. (Contributed by Barney Gale in gh-74033.)

  • Remove support for passing additional positional arguments to PurePath.relative_to() and is_relative_to(). In previous versions, any such arguments are joined onto other. (Contributed by Barney Gale in gh-78707.)

pkgutil

  • Remove the get_loader() and find_loader() functions, which have been deprecated since Python 3.12. (Contributed by Bénédikt Tran in gh-97850.)

pty

  • Remove the master_open() and slave_open() functions, which have been deprecated since Python 3.12. Use pty.openpty() instead. (Contributed by Nikita Sobolev in gh-118824.)

sqlite3

urllib

  • Remove the Quoter class from urllib.parse, which has been deprecated since Python 3.11. (Contributed by Nikita Sobolev in gh-118827.)

  • Remove the URLopener and FancyURLopener classes from urllib.request, which have been deprecated since Python 3.3.

    myopener.open() can be replaced with urlopen(). myopener.retrieve() can be replaced with urlretrieve(). Customisations to the opener classes can be replaced by passing customized handlers to build_opener(). (Contributed by Barney Gale in gh-84850.)

Deprecated

New deprecations

Pending removal in Python 3.15

  • The import system:

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

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

  • ctypes:

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

  • http.server:

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

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

  • importlib:

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

  • locale:

  • pathlib:

  • platform:

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

  • sysconfig:

  • threading:

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

  • types:

  • typing:

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

    • When using the functional syntax of TypedDicts, failing to pass a value to the fields parameter (TD = TypedDict("TD")) or passing None (TD = TypedDict("TD", None)) has been deprecated since Python 3.13. Use class TD(TypedDict): pass or TD = TypedDict("TD", {}) to create a TypedDict with zero field.

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

  • wave:

  • zipimport:

Pending removal in Python 3.16

Pending removal in Python 3.17

  • collections.abc:

    • collections.abc.ByteString is scheduled for removal in Python 3.17.

      Use isinstance(obj, collections.abc.Buffer) to test if obj implements the buffer protocol at runtime. For use in type annotations, either use Buffer or a union that explicitly specifies the types your code supports (e.g., bytes | bytearray | memoryview).

      ByteString was originally intended to be an abstract class that would serve as a supertype of both bytes and bytearray. However, since the ABC never had any methods, knowing that an object was an instance of ByteString never actually told you anything useful about the object. Other common buffer types such as memoryview were also never understood as subtypes of ByteString (either at runtime or by static type checkers).

      See PEP 688 for more details. (Contributed by Shantanu Jain in gh-91896.)

  • typing:

    • Before Python 3.14, old-style unions were implemented using the private class typing._UnionGenericAlias. This class is no longer needed for the implementation, but it has been retained for backward compatibility, with removal scheduled for Python 3.17. Users should use documented introspection helpers like typing.get_origin() and typing.get_args() instead of relying on private implementation details.

    • typing.ByteString, deprecated since Python 3.9, is scheduled for removal in Python 3.17.

      Use isinstance(obj, collections.abc.Buffer) to test if obj implements the buffer protocol at runtime. For use in type annotations, either use Buffer or a union that explicitly specifies the types your code supports (e.g., bytes | bytearray | memoryview).

      ByteString was originally intended to be an abstract class that would serve as a supertype of both bytes and bytearray. However, since the ABC never had any methods, knowing that an object was an instance of ByteString never actually told you anything useful about the object. Other common buffer types such as memoryview were also never understood as subtypes of ByteString (either at runtime or by static type checkers).

      See PEP 688 for more details. (Contributed by Shantanu Jain in gh-91896.)

Pending removal in Python 3.19

  • ctypes:

    • Implicitly switching to the MSVC-compatible struct layout by setting _pack_ but not _layout_ on non-Windows platforms.

Pending removal in future versions

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

  • argparse:

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

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

    • The argparse.FileType type converter is deprecated.

  • builtins:

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

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

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

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

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

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

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

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

  • codecs: use open() instead of codecs.open(). (gh-133038)

  • 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:

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

  • importlib.metadata:

    • EntryPoints tuple interface.

    • Implicit None on return values.

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

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

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

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

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

  • sre_compile, sre_constants and sre_parse modules.

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

  • ssl options and protocols:

    • ssl.SSLContext without protocol argument is deprecated.

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

    • ssl.OP_NO_SSL* options

    • ssl.OP_NO_TLS* options

    • ssl.PROTOCOL_SSLv3

    • ssl.PROTOCOL_TLS

    • ssl.PROTOCOL_TLSv1

    • ssl.PROTOCOL_TLSv1_1

    • ssl.PROTOCOL_TLSv1_2

    • ssl.TLSVersion.SSLv3

    • ssl.TLSVersion.TLSv1

    • ssl.TLSVersion.TLSv1_1

  • threading methods:

  • typing.Text (gh-92332).

  • The internal class typing._UnionGenericAlias is no longer used to implement typing.Union. To preserve compatibility with users using this private class, a compatibility shim will be provided until at least Python 3.17. (Contributed by Jelle Zijlstra in gh-105499.)

  • 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()

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

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

  • sys._clear_type_cache() is deprecated: use sys._clear_internal_caches() instead.

CPython bytecode changes

Pseudo-instructions

  • Add the ANNOTATIONS_PLACEHOLDER pseudo instruction to support partially executed module-level annotations with deferred evaluation of annotations. (Contributed by Jelle Zijlstra in gh-130907.)

  • Add the BINARY_OP_EXTEND pseudo instruction, which executes a pair of functions (guard and specialization functions) accessed from the inline cache. (Contributed by Irit Katriel in gh-100239.)

  • Add three specializations for CALL_KW; CALL_KW_PY for calls to Python functions, CALL_KW_BOUND_METHOD for calls to bound methods, and CALL_KW_NON_PY for all other calls. (Contributed by Mark Shannon in gh-118093.)

  • Add the JUMP_IF_TRUE and JUMP_IF_FALSE pseudo instructions, conditional jumps which do not impact the stack. Replaced by the sequence COPY 1, TO_BOOL, POP_JUMP_IF_TRUE/FALSE. (Contributed by Irit Katriel in gh-124285.)

  • Add the LOAD_CONST_MORTAL pseudo instruction. (Contributed by Mark Shannon in gh-128685.)

  • Add the LOAD_CONST_IMMORTAL pseudo instruction, which does the same as LOAD_CONST, but is more efficient for immortal objects. (Contributed by Mark Shannon in gh-125837.)

  • Add the NOT_TAKEN pseudo instruction, used by sys.monitoring to record branch events (such as BRANCH_LEFT). (Contributed by Mark Shannon in gh-122548.)

C API changes

Python configuration C API

Add a PyInitConfig C API to configure the Python initialization without relying on C structures and the ability to make ABI-compatible changes in the future.

Complete the PEP 587 PyConfig C API by adding PyInitConfig_AddModule() which can be used to add a built-in extension module; a feature previously referred to as the “inittab”.

Add PyConfig_Get() and PyConfig_Set() functions to get and set the current runtime configuration.

PEP 587 ‘Python Initialization Configuration’ unified all the ways to configure Python’s initialization. This PEP also unifies the configuration of Python’s preinitialization and initialization in a single API. Moreover, this PEP only provides a single choice to embed Python, instead of having two ‘Python’ and ‘Isolated’ choices (PEP 587), to further simplify the API.

The lower level PEP 587 PyConfig API remains available for use cases with an intentionally higher level of coupling to CPython implementation details (such as emulating the full functionality of CPython’s CLI, including its configuration mechanisms).

(Contributed by Victor Stinner in gh-107954.)

New features in the C API

Limited C API changes

Removed C APIs

  • Creating immutable types with mutable bases was deprecated in Python 3.12, and now raises a TypeError. (Contributed by Nikita Sobolev in gh-119775.)

  • Remove PyDictObject.ma_version_tag member, which was deprecated in Python 3.12. Use the PyDict_AddWatcher() API instead. (Contributed by Sam Gross in gh-124296.)

  • Remove the private _Py_InitializeMain() function. It was a provisional API added to Python 3.8 by PEP 587. (Contributed by Victor Stinner in gh-129033.)

  • Remove the undocumented APIs Py_C_RECURSION_LIMIT and PyThreadState.c_recursion_remaining. These were added in 3.13 and have been removed without deprecation. Use Py_EnterRecursiveCall() to guard against runaway recursion in C code. (Removed by Petr Viktorin in gh-133079, see also gh-130396.)

Deprecated C APIs

Pending removal in Python 3.15

Pending removal in Python 3.16

  • The bundled copy of libmpdec.

Pending removal in Python 3.18

Pending removal in future versions

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

Build changes

  • PEP 776: Emscripten is now an officially supported platform at tier 3. As a part of this effort, more than 25 bugs in Emscripten libc were fixed. Emscripten now includes support for ctypes, termios, and fcntl, as well as experimental support for the new default interactive shell. (Contributed by R. Hood Chatham in gh-127146, gh-127683, and gh-136931.)

  • Official Android binary releases are now provided on python.org.

  • GNU Autoconf 2.72 is now required to generate configure. (Contributed by Erlend Aasland in gh-115765.)

  • wasm32-unknown-emscripten is now a PEP 11 tier 3 platform. (Contributed by R. Hood Chatham in gh-127146, gh-127683, and gh-136931.)

  • #pragma-based linking with python3*.lib can now be switched off with Py_NO_LINK_LIB. (Contributed by Jean-Christophe Fillion-Robin in gh-82909.)

  • CPython now enables a set of recommended compiler options by default for improved security. Use the --disable-safety configure option to disable them, or the --enable-slower-safety option for a larger set of compiler options, albeit with a performance cost.

  • The WITH_FREELISTS macro and --without-freelists configure option have been removed.

  • The new configure option --with-tail-call-interp may be used to enable the experimental tail call interpreter. See A new type of interpreter for further details.

  • To disable the new remote debugging support, use the --without-remote-debug configure option. This may be useful for security reasons.

  • iOS and macOS apps can now be configured to redirect stdout and stderr content to the system log. (Contributed by Russell Keith-Magee in gh-127592.)

  • The iOS testbed is now able to stream test output while the test is running. The testbed can also be used to run the test suite of projects other than CPython itself. (Contributed by Russell Keith-Magee in gh-127592.)

build-details.json

Installations of Python now contain a new file, build-details.json. This is a static JSON document containing build details for CPython, to allow for introspection without needing to run code. This is helpful for use-cases such as Python launchers, cross-compilation, and so on.

build-details.json must be installed in the platform-independent standard library directory. This corresponds to the ‘stdlib’ sysconfig installation path, which can be found by running sysconfig.get_path('stdlib').

See also

PEP 739 – build-details.json 1.0 – a static description file for Python build details

Discontinuation of PGP signatures

PGP (Pretty Good Privacy) signatures will not be provided for releases of Python 3.14 or future versions. To verify CPython artifacts, users must use Sigstore verification materials. Releases have been signed using Sigstore since Python 3.11.

This change in release process was specified in PEP 761.

Free-threaded Python is officially supported

The free-threaded build of Python is now supported and no longer experimental. This is the start of phase II where free-threaded Python is officially supported but still optional.

The free-threading team are confident that the project is on the right path, and appreciate the continued dedication from everyone working to make free-threading ready for broader adoption across the Python community.

With these recommendations and the acceptance of this PEP, the Python developer community should broadly advertise that free-threading is a supported Python build option now and into the future, and that it will not be removed without a proper deprecation schedule.

Any decision to transition to phase III, with free-threading as the default or sole build of Python is still undecided, and dependent on many factors both within CPython itself and the community. This decision is for the future.

Binary releases for the experimental just-in-time compiler

The official macOS and Windows release binaries now include an experimental just-in-time (JIT) compiler. Although it is not recommended for production use, it can be tested by setting PYTHON_JIT=1 as an environment variable. Downstream source builds and redistributors can use the --enable-experimental-jit=yes-off configuration option for similar behavior.

The JIT is at an early stage and still in active development. As such, the typical performance impact of enabling it can range from 10% slower to 20% faster, depending on workload. To aid in testing and evaluation, a set of introspection functions has been provided in the sys._jit namespace. sys._jit.is_available() can be used to determine if the current executable supports JIT compilation, while sys._jit.is_enabled() can be used to tell if JIT compilation has been enabled for the current process.

Currently, the most significant missing functionality is that native debuggers and profilers like gdb and perf are unable to unwind through JIT frames (Python debuggers and profilers, like pdb or profile, continue to work without modification). Free-threaded builds do not support JIT compilation.

Please report any bugs or major performance regressions that you encounter!

Porting to Python 3.14

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

Changes in the Python API

  • On Unix platforms other than macOS, forkserver is now the default start method for multiprocessing and ProcessPoolExecutor, instead of fork.

    See (1) and (2) for details.

    If you encounter NameErrors or pickling errors coming out of multiprocessing or concurrent.futures, see the forkserver restrictions.

    This change does not affect Windows or macOS, where ‘spawn’ remains the default start method.

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

  • The garbage collector is now incremental, which means that the behavior of gc.collect() changes slightly:

    • gc.collect(1): Performs an increment of garbage collection, rather than collecting generation 1.

    • Other calls to gc.collect() are unchanged.

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

  • types.UnionType is now an alias for typing.Union, causing changes in some behaviors. See above for more details. (Contributed by Jelle Zijlstra in gh-105499.)

  • The runtime behavior of annotations has changed in various ways; see above for details. While most code that interacts with annotations should continue to work, some undocumented details may behave differently.

  • As part of making the mimetypes CLI public, it now exits with 1 on failure instead of 0 and 2 on incorrect command-line parameters instead of 1. Error messages are now printed to stderr.

  • The \B pattern in regular expression now matches the empty string when given as the entire pattern, which may cause behavioural changes.

  • On FreeBSD, sys.platform no longer contains the major version number.

Changes in annotations (PEP 649 and PEP 749)

This section contains guidance on changes that may be needed to annotations or Python code that interacts with or introspects annotations, due to the changes related to deferred evaluation of annotations.

In the majority of cases, working code from older versions of Python will not require any changes.

Implications for annotated code

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

You will likely be able to remove quoted strings in annotations, which are frequently used for forward references. Similarly, if you use from __future__ import annotations to avoid having to write strings in annotations, you may well be able to remove that import once you support only Python 3.14 and newer. However, if you rely on third-party libraries that read annotations, those libraries may need changes to support unquoted annotations before they work as expected.

Implications for readers of __annotations__

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

The external typing_extensions package provides partial backports of some of the functionality of the annotationlib module, such as the Format enum and the get_annotations() function. These can be used to write cross-version code that takes advantage of the new behavior in Python 3.14.

from __future__ import annotations

In Python 3.7, PEP 563 introduced the from __future__ import annotations future statement, which turns all annotations into strings.

However, this statement is now deprecated and it is expected to be removed in a future version of Python. This removal will not happen until after Python 3.13 reaches its end of life in 2029, being the last version of Python without support for deferred evaluation of annotations.

In Python 3.14, the behavior of code using from __future__ import annotations is unchanged.

Changes in the C API

  • Py_Finalize() now deletes all interned strings. This is backwards incompatible to any C extension that holds onto an interned string after a call to Py_Finalize() and is then reused after a call to Py_Initialize(). Any issues arising from this behavior will normally result in crashes during the execution of the subsequent call to Py_Initialize() from accessing uninitialized memory. To fix, use an address sanitizer to identify any use-after-free coming from an interned string and deallocate it during module shutdown. (Contributed by Eddie Elizondo in gh-113601.)

  • The Unicode Exception Objects C API now raises a TypeError if its exception argument is not a UnicodeError object. (Contributed by Bénédikt Tran in gh-127691.)