What’s new in Python 3.14¶

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.)

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:

• A PYTHON_DISABLE_REMOTE_DEBUG environment variable.

• A -X disable-remote-debug command-line option.

• A --without-remote-debug configure flag to completely disable the feature at build time.

(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.

(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.)

Built-ins¶

• The bytes.fromhex() and bytearray.fromhex() methods now accept ASCII bytes and bytes-like objects. (Contributed by Daniel Pope in gh-129349.)

• Add class methods float.from_number() and complex.from_number() to convert a number to float or complex type correspondingly. They raise a TypeError if the argument is not a real number. (Contributed by Serhiy Storchaka in gh-84978.)

• Support underscore and comma as thousands separators in the fractional part for floating-point presentation types of the new-style string formatting (with format() or f-strings). (Contributed by Sergey B Kirpichev in gh-87790.)

• The int() function no longer delegates to __trunc__(). Classes that want to support conversion to int() must implement either __int__() or __index__(). (Contributed by Mark Dickinson in gh-119743.)

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

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

• Using NotImplemented in a boolean context will now raise a TypeError. This has raised a DeprecationWarning since Python 3.9. (Contributed by Jelle Zijlstra in gh-118767.)

• Three-argument pow() now tries calling __rpow__() if necessary. Previously it was only called in two-argument pow() and the binary power operator. (Contributed by Serhiy Storchaka in gh-130104.)

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

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.)

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¶

• The function and methods named create_task() now take an arbitrary list of keyword arguments. All keyword arguments are passed to the Task constructor or the custom task factory. (See set_task_factory() for details.) The name and context keyword arguments are no longer special; the name should now be set using the name keyword argument of the factory, and context may be None.

  This affects the following function and methods: asyncio.create_task(), asyncio.loop.create_task(), asyncio.TaskGroup.create_task().

  (Contributed by Thomas Grainger in gh-128307.)

• There are two new utility functions for introspecting and printing a program’s call graph: capture_call_graph() and print_call_graph(). See Asyncio introspection capabilities for more details. (Contributed by Yury Selivanov, Pablo Galindo Salgado, and Łukasz Langa in gh-91048.)

calendar¶

• By default, today’s date is highlighted in color in calendar’s command-line text output. This can be controlled by environment variables. (Contributed by Hugo van Kemenade in gh-128317.)

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 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¶

• Support the context manager protocol for Token objects. (Contributed by Andrew Svetlov in gh-129889.)

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¶

• Add the assume_default_colors() function, a refinement of the use_default_colors() function which allows changing the color pair 0. (Contributed by Serhiy Storchaka in gh-133139.)

datetime¶

• Add the strptime() method to the datetime.date and datetime.time classes. (Contributed by Wannes Boeykens in gh-41431.)

decimal¶

• Add Decimal.from_number() as an alternative constructor for Decimal. (Contributed by Serhiy Storchaka in gh-121798.)

• Expose IEEEContext() to support creation of contexts corresponding to the IEEE 754 (2008) decimal interchange formats. (Contributed by Sergey B Kirpichev in gh-53032.)

difflib¶

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

dis¶

• Add support for rendering full source location information of instructions, rather than only the line number. This feature is added to the following interfaces via the show_positions keyword argument:

  • dis.Bytecode

  • dis.dis()

  • dis.distb()

  • dis.disassemble()

  This feature is also exposed via dis --show-positions. (Contributed by Bénédikt Tran in gh-123165.)

• Add the dis --specialized command-line option to show specialized bytecode. (Contributed by Bénédikt Tran in gh-127413.)

errno¶

• Add the EHWPOISON error code constant. (Contributed by James Roy in gh-126585.)

faulthandler¶

• Add support for printing the C stack trace on systems that support it via the new dump_c_stack() function or via the c_stack argument in faulthandler.enable(). (Contributed by Peter Bierma in gh-127604.)

fnmatch¶

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

fractions¶

• A Fraction object may now be constructed from any object with the as_integer_ratio() method. (Contributed by Serhiy Storchaka in gh-82017.)

• Add Fraction.from_number() as an alternative constructor for Fraction. (Contributed by Serhiy Storchaka in gh-121797.)

functools¶

• Add the Placeholder sentinel. This may be used with the partial() or partialmethod() functions to reserve a place for positional arguments in the returned partial object. (Contributed by Dominykas Grigonis in gh-119127.)

• Allow the initial parameter of reduce() to be passed as a keyword argument. (Contributed by Sayandip Dutta in gh-125916.)

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¶

• Allow TopologicalSorter.prepare() to be called more than once as long as sorting has not started. (Contributed by Daniel Pope in gh-130914.)

heapq¶

• The heapq module has improved support for working with max-heaps, via the following new functions:

  • heapify_max()

  • heappush_max()

  • heappop_max()

  • heapreplace_max()

  • heappushpop_max()

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:

  • --tls-cert <path>: Path to the TLS certificate file.

  • --tls-key <path>: Optional path to the private key file.

  • --tls-password-file <path>: Optional path to the password file for the private key.

  (Contributed by Semyon Moroz in gh-85162.)

imaplib¶

• Add IMAP4.idle(), implementing the IMAP4 IDLE command as defined in RFC 2177. (Contributed by Forest in gh-55454.)

inspect¶

• signature() takes a new argument annotation_format to control the annotationlib.Format used for representing annotations. (Contributed by Jelle Zijlstra in gh-101552.)

• Signature.format() takes a new argument unquote_annotations. If true, string annotations are displayed without surrounding quotes. (Contributed by Jelle Zijlstra in gh-101552.)

• Add function ispackage() to determine whether an object is a package or not. (Contributed by Zhikang Yan in gh-125634.)

io¶

• Reading text from a non-blocking stream with read may now raise a BlockingIOError if the operation cannot immediately return bytes. (Contributed by Giovanni Siragusa in gh-109523.)

• Add the Reader and Writer protocols as simpler alternatives to the pseudo-protocols typing.IO, typing.TextIO, and typing.BinaryIO. (Contributed by Sebastian Rittau in gh-127648.)

json¶

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

• Allow using the json module as a script using the -m switch: python -m json. This is now preferred to python -m json.tool, which is soft deprecated. See the JSON command-line interface documentation. (Contributed by Trey Hunner in gh-122873.)

• By default, the output of the JSON command-line interface is highlighted in color. This can be controlled by environment variables. (Contributed by Tomas Roun in gh-131952.)

linecache¶

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

logging.handlers¶

• QueueListener objects now support the context manager protocol. (Contributed by Charles Machalow in gh-132106.)

• QueueListener.start now raises a RuntimeError if the listener is already started. (Contributed by Charles Machalow in gh-132106.)

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 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¶

• Add the reload_environ() function to update os.environ and os.environb with changes to the environment made by os.putenv(), by os.unsetenv(), or made outside Python in the same process. (Contributed by Victor Stinner in gh-120057.)

• Add the SCHED_DEADLINE and SCHED_NORMAL constants to the os module. (Contributed by James Roy in gh-127688.)

• Add the readinto() function to read into a buffer object from a file descriptor. (Contributed by Cody Maloney in gh-129205.)

os.path¶

• The strict parameter to realpath() accepts a new value, ALLOW_MISSING. If used, errors other than FileNotFoundError will be re-raised; the resulting path can be missing but it will be free of symlinks. (Contributed by Petr Viktorin for CVE 2025-4517.)

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:

  python -m pdb -p 1234
  

  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¶

• Add invalidate_caches(), a function to invalidate cached results in the platform module. (Contributed by Bénédikt Tran in gh-122549.)

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¶

• Expose the following Symbol methods:

  • is_comp_cell()

  • is_comp_iter()

  • is_free_class()

  (Contributed by Bénédikt Tran in gh-120029.)

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¶

• Add two new monitoring events, BRANCH_LEFT and BRANCH_RIGHT. These replace and deprecate the BRANCH event. (Contributed by Mark Shannon in gh-122548.)

sysconfig¶

• Add ABIFLAGS key to get_config_vars() on Windows. (Contributed by Xuehai Pan in gh-131799.)

tarfile¶

• data_filter() now normalizes symbolic link targets in order to avoid path traversal attacks. (Contributed by Petr Viktorin in gh-127987 and CVE 2025-4138.)

• extractall() now skips fixing up directory attributes when a directory was removed or replaced by another kind of file. (Contributed by Petr Viktorin in gh-127987 and CVE 2024-12718.)

• extract() and extractall() now (re-)apply the extraction filter when substituting a link (hard or symbolic) with a copy of another archive member, and when fixing up directory attributes. The former raises a new exception, LinkFallbackError. (Contributed by Petr Viktorin for CVE 2025-4330 and CVE 2024-12718.)

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

threading¶

• threading.Thread.start() now sets the operating system thread name to threading.Thread.name. (Contributed by Victor Stinner in gh-59705.)

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¶

• Add context managers for turtle.fill(), turtle.poly(), and turtle.no_animation(). (Contributed by Marie Roald and Yngve Mardal Moe in gh-126350.)

types¶

• types.UnionType is now an alias for typing.Union. See below for more details. (Contributed by Jelle Zijlstra in gh-105499.)

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¶

• unittest output is now colored by default. This can be controlled by environment variables. (Contributed by Hugo van Kemenade in gh-127221.)

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

• A number of new methods were added in the TestCase class that provide more specialized tests.

  • assertHasAttr() and assertNotHasAttr() check whether the object has a particular attribute.

  • assertIsSubclass() and assertNotIsSubclass() check whether the object is a subclass of a particular class, or of one of a tuple of classes.

  • assertStartsWith(), assertNotStartsWith(), assertEndsWith() and assertNotEndsWith() check whether the Unicode or byte string starts or ends with particular strings.

  (Contributed by Serhiy Storchaka in gh-71339.)

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¶

• Add support for UUID versions 6, 7, and 8 via uuid6(), uuid7(), and uuid8() respectively, as specified in RFC 9562. (Contributed by Bénédikt Tran in gh-89083.)

• NIL and MAX are now available to represent the Nil and Max UUID formats as defined by RFC 9562. (Contributed by Nick Pope in gh-128427.)

• Allow generating multiple UUIDs simultaneously on the command-line via python -m uuid --count. (Contributed by Simon Legner in gh-131236.)

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¶

• Added ZipInfo._for_archive, a method to resolve suitable defaults for a ZipInfo object as used by ZipFile.writestr. (Contributed by Bénédikt Tran in gh-123424.)

• ZipFile.writestr() now respects the SOURCE_DATE_EPOCH environment variable in order to better support reproducible builds. (Contributed by Jiahao Li in gh-91279.)

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¶

• pdb now supports two backends, based on either sys.settrace() or sys.monitoring. Using the pdb CLI or breakpoint() will always use the sys.monitoring backend. Explicitly instantiating pdb.Pdb and its derived classes will use the sys.settrace() backend by default, which is configurable. (Contributed by Tian Gao in gh-124533.)

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.)

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¶

• Remove deprecated importlib.abc classes:

  • ResourceReader (use TraversableResources)

  • Traversable (use Traversable)

  • TraversableResources (use TraversableResources)

  (Contributed by Jason R. Coombs and Hugo van Kemenade in gh-93963.)

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¶

• Remove version and version_info from the sqlite3 module; use sqlite_version and sqlite_version_info for the actual version number of the runtime SQLite library. (Contributed by Hugo van Kemenade in gh-118924.)

• Using a sequence of parameters with named placeholders now raises a ProgrammingError, having been deprecated since Python 3.12. (Contributed by Erlend E. Aasland in gh-118928 and gh-101693.)

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.)

New deprecations¶

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

• argparse:

  • Passing the undocumented keyword argument prefix_chars to the add_argument_group() method is now deprecated. (Contributed by Savannah Ostrowski in gh-125563.)

  • Deprecated the argparse.FileType type converter. Anything relating to resource management should be handled downstream, after the arguments have been parsed. (Contributed by Serhiy Storchaka in gh-58032.)

• asyncio:

  • The asyncio.iscoroutinefunction() is now deprecated and will be removed in Python 3.16; use inspect.iscoroutinefunction() instead. (Contributed by Jiahao Li and Kumar Aditya in gh-122875.)

  • The asyncio policy system is deprecated and will be removed in Python 3.16. In particular, the following classes and functions are deprecated:

    • asyncio.AbstractEventLoopPolicy

    • asyncio.DefaultEventLoopPolicy

    • asyncio.WindowsSelectorEventLoopPolicy

    • asyncio.WindowsProactorEventLoopPolicy

    • asyncio.get_event_loop_policy()

    • asyncio.set_event_loop_policy()

    Users should use asyncio.run() or asyncio.Runner with the loop_factory argument to use the desired event loop implementation.

    For example, to use asyncio.SelectorEventLoop on Windows:

    import asyncio
    
    async def main():
        ...
    
    asyncio.run(main(), loop_factory=asyncio.SelectorEventLoop)
    

    (Contributed by Kumar Aditya in gh-127949.)

• codecs: The codecs.open() function is now deprecated, and will be removed in a future version of Python. Use open() instead. (Contributed by Inada Naoki in gh-133036.)

• ctypes:

  • On non-Windows platforms, setting Structure._pack_ to use a MSVC-compatible default memory layout is now deprecated in favor of setting Structure._layout_ to 'ms', and will be removed in Python 3.19. (Contributed by Petr Viktorin in gh-131747.)

  • Calling ctypes.POINTER() on a string is now deprecated. Use incomplete types for self-referential structures. Also, the internal ctypes._pointer_type_cache is deprecated. See ctypes.POINTER() for updated implementation details. (Contributed by Sergey Myrianov in gh-100926.)

• functools: Calling the Python implementation of functools.reduce() with function or sequence as keyword arguments is now deprecated; the parameters will be made positional-only in Python 3.16. (Contributed by Kirill Podoprigora in gh-121676.)

• logging: Support for custom logging handlers with the strm argument is now deprecated and scheduled for removal in Python 3.16. Define handlers with the stream argument instead. (Contributed by Mariusz Felisiak in gh-115032.)

• mimetypes: Valid extensions are either empty or must start with ‘.’ for mimetypes.MimeTypes.add_type(). Undotted extensions are deprecated and will raise a ValueError in Python 3.16. (Contributed by Hugo van Kemenade in gh-75223.)

• nturl2path: This module is now deprecated. Call urllib.request.url2pathname() and pathname2url() instead. (Contributed by Barney Gale in gh-125866.)

• os: The os.popen() and os.spawn* functions are now soft deprecated. They should no longer be used to write new code. The subprocess module is recommended instead. (Contributed by Victor Stinner in gh-120743.)

• pathlib: pathlib.PurePath.as_uri() is now deprecated and scheduled for removal in Python 3.19. Use pathlib.Path.as_uri() instead. (Contributed by Barney Gale in gh-123599.)

• pdb: The undocumented pdb.Pdb.curframe_locals attribute is now a deprecated read-only property, which will be removed in a future version of Python. The low overhead dynamic frame locals access added in Python 3.13 by PEP 667 means the frame locals cache reference previously stored in this attribute is no longer needed. Derived debuggers should access pdb.Pdb.curframe.f_locals directly in Python 3.13 and later versions. (Contributed by Tian Gao in gh-124369 and gh-125951.)

• symtable: Deprecate symtable.Class.get_methods() due to the lack of interest, scheduled for removal in Python 3.16. (Contributed by Bénédikt Tran in gh-119698.)

• tkinter: The tkinter.Variable methods trace_variable(), trace_vdelete() and trace_vinfo() are now deprecated. Use trace_add(), trace_remove() and trace_info() instead. (Contributed by Serhiy Storchaka in gh-120220.)

• urllib.parse: Accepting objects with false values (like 0 and []) except empty strings, bytes-like objects and None in parse_qsl() and parse_qs() is now deprecated. (Contributed by Serhiy Storchaka in gh-116897.)

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:

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

• pathlib:

  • PurePath.is_reserved() has been deprecated since Python 3.13. Use os.path.isreserved() to detect reserved paths on Windows.

• 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:

  • The check_home argument of sysconfig.is_python_build() has been deprecated since Python 3.12.

• 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:

  • types.CodeType: Accessing co_lnotab was deprecated in PEP 626 since 3.10 and was planned to be removed in 3.12, but it only got a proper DeprecationWarning in 3.12. May be removed in 3.15. (Contributed by Nikita Sobolev in gh-101866.)

• 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:

  • The getmark(), setmark(), and getmarkers() methods of the Wave_read and Wave_write classes have been deprecated since Python 3.13.

• zipimport:

  • load_module() has been deprecated since Python 3.10. Use exec_module() instead. (Contributed by Jiahao Li in gh-125746.)

Pending removal in Python 3.16¶

• The import system:

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

• array:

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

• asyncio:

  • asyncio.iscoroutinefunction() is deprecated and will be removed in Python 3.16; use inspect.iscoroutinefunction() instead. (Contributed by Jiahao Li and Kumar Aditya in gh-122875.)

  • asyncio policy system is deprecated and will be removed in Python 3.16. In particular, the following classes and functions are deprecated:

    • asyncio.AbstractEventLoopPolicy

    • asyncio.DefaultEventLoopPolicy

    • asyncio.WindowsSelectorEventLoopPolicy

    • asyncio.WindowsProactorEventLoopPolicy

    • asyncio.get_event_loop_policy()

    • asyncio.set_event_loop_policy()

    Users should use asyncio.run() or asyncio.Runner with loop_factory to use the desired event loop implementation.

    For example, to use asyncio.SelectorEventLoop on Windows:

    import asyncio
    
    async def main():
        ...
    
    asyncio.run(main(), loop_factory=asyncio.SelectorEventLoop)
    

    (Contributed by Kumar Aditya in gh-127949.)

• builtins:

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

• functools:

  • Calling the Python implementation of functools.reduce() with function or sequence as keyword arguments has been deprecated since Python 3.14.

• logging:

  Support for custom logging handlers with the strm argument is deprecated and scheduled for removal in Python 3.16. Define handlers with the stream argument instead. (Contributed by Mariusz Felisiak in gh-115032.)

• mimetypes:

  • Valid extensions start with a ‘.’ or are empty for mimetypes.MimeTypes.add_type(). Undotted extensions are deprecated and will raise a ValueError in Python 3.16. (Contributed by Hugo van Kemenade in gh-75223.)

• shutil:

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

• symtable:

  • The Class.get_methods method has been deprecated since Python 3.14.

• sys:

  • The _enablelegacywindowsfsencoding() function has been deprecated since Python 3.13. Use the PYTHONLEGACYWINDOWSFSENCODING environment variable instead.

• sysconfig:

  • The sysconfig.expand_makefile_vars() function has been deprecated since Python 3.14. Use the vars argument of sysconfig.get_paths() instead.

• tarfile:

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

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:

  • threading.Condition.notifyAll(): use notify_all().

  • threading.Event.isSet(): use is_set().

  • threading.Thread.isDaemon(), threading.Thread.setDaemon(): use threading.Thread.daemon attribute.

  • threading.Thread.getName(), threading.Thread.setName(): use threading.Thread.name attribute.

  • threading.currentThread(): use threading.current_thread().

  • threading.activeCount(): use threading.active_count().

• 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.

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.)

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¶

• Add Py_PACK_VERSION() and Py_PACK_FULL_VERSION(), two new macros for bit-packing Python version numbers. This is useful for comparisons with Py_Version or PY_VERSION_HEX. (Contributed by Petr Viktorin in gh-128629.)

• Add PyBytes_Join(sep, iterable) function, similar to sep.join(iterable) in Python. (Contributed by Victor Stinner in gh-121645.)

• Add functions to manipulate the configuration of the current runtime Python interpreter (PEP 741: Python configuration C API):

  • PyConfig_Get()

  • PyConfig_GetInt()

  • PyConfig_Set()

  • PyConfig_Names()

  (Contributed by Victor Stinner in gh-107954.)

• Add functions to configure Python initialization (PEP 741: Python configuration C API):

  • Py_InitializeFromInitConfig()

  • PyInitConfig_AddModule()

  • PyInitConfig_Create()

  • PyInitConfig_Free()

  • PyInitConfig_FreeStrList()

  • PyInitConfig_GetError()

  • PyInitConfig_GetExitCode()

  • PyInitConfig_GetInt()

  • PyInitConfig_GetStr()

  • PyInitConfig_GetStrList()

  • PyInitConfig_HasOption()

  • PyInitConfig_SetInt()

  • PyInitConfig_SetStr()

  • PyInitConfig_SetStrList()

  (Contributed by Victor Stinner in gh-107954.)

• Add Py_fopen() function to open a file. This works similarly to the standard C fopen() function, instead accepting a Python object for the path parameter and setting an exception on error. The corresponding new Py_fclose() function should be used to close a file. (Contributed by Victor Stinner in gh-127350.)

• Add Py_HashBuffer() to compute and return the hash value of a buffer. (Contributed by Antoine Pitrou and Victor Stinner in gh-122854.)

• Add PyImport_ImportModuleAttr() and PyImport_ImportModuleAttrString() helper functions to import a module and get an attribute of the module. (Contributed by Victor Stinner in gh-128911.)

• Add PyIter_NextItem() to replace PyIter_Next(), which has an ambiguous return value. (Contributed by Irit Katriel and Erlend Aasland in gh-105201.)

• Add PyLong_GetSign() function to get the sign of int objects. (Contributed by Sergey B Kirpichev in gh-116560.)

• Add PyLong_IsPositive(), PyLong_IsNegative() and PyLong_IsZero() for checking if PyLongObject is positive, negative, or zero, respectively. (Contributed by James Roy and Sergey B Kirpichev in gh-126061.)

• Add new functions to convert C <stdint.h> numbers to/from Python int objects:

  • PyLong_AsInt32()

  • PyLong_AsInt64()

  • PyLong_AsUInt32()

  • PyLong_AsUInt64()

  • PyLong_FromInt32()

  • PyLong_FromInt64()

  • PyLong_FromUInt32()

  • PyLong_FromUInt64()

  (Contributed by Victor Stinner in gh-120389.)

• Add a new import and export API for Python int objects (PEP 757):

  • PyLong_GetNativeLayout()

  • PyLong_Export()

  • PyLong_FreeExport()

  • PyLongWriter_Create()

  • PyLongWriter_Finish()

  • PyLongWriter_Discard()

  (Contributed by Sergey B Kirpichev and Victor Stinner in gh-102471.)

• Add PyMonitoring_FireBranchLeftEvent() and PyMonitoring_FireBranchRightEvent() for generating BRANCH_LEFT and BRANCH_RIGHT events, respectively. (Contributed by Mark Shannon in gh-122548.)

• Add PyType_Freeze() function to make a type immutable. (Contributed by Victor Stinner in gh-121654.)

• Add PyType_GetBaseByToken() and Py_tp_token slot for easier superclass identification, which attempts to resolve the type checking issue mentioned in PEP 630. (Contributed in gh-124153.)

• Add a new PyUnicode_Equal() function to test if two strings are equal. The function is also added to the Limited C API. (Contributed by Victor Stinner in gh-124502.)

• Add a new PyUnicodeWriter API to create a Python str object, with the following functions:

  • PyUnicodeWriter_Create()

  • PyUnicodeWriter_DecodeUTF8Stateful()

  • PyUnicodeWriter_Discard()

  • PyUnicodeWriter_Finish()

  • PyUnicodeWriter_Format()

  • PyUnicodeWriter_WriteASCII()

  • PyUnicodeWriter_WriteChar()

  • PyUnicodeWriter_WriteRepr()

  • PyUnicodeWriter_WriteStr()

  • PyUnicodeWriter_WriteSubstring()

  • PyUnicodeWriter_WriteUCS4()

  • PyUnicodeWriter_WriteUTF8()

  • PyUnicodeWriter_WriteWideChar()

  (Contributed by Victor Stinner in gh-119182.)

• The k and K formats in PyArg_ParseTuple() and similar functions now use __index__() if available, like all other integer formats. (Contributed by Serhiy Storchaka in gh-112068.)

• Add support for a new p format unit in Py_BuildValue() that produces a Python bool object from a C integer. (Contributed by Pablo Galindo in bpo-45325.)

• Add PyUnstable_IsImmortal() for determining if an object is immortal, for debugging purposes. (Contributed by Peter Bierma in gh-128509.)

• Add PyUnstable_Object_EnableDeferredRefcount() for enabling deferred reference counting, as outlined in PEP 703.

• Add PyUnstable_Object_IsUniquelyReferenced() as a replacement for Py_REFCNT(op) == 1 on free threaded builds. (Contributed by Peter Bierma in gh-133140.)

• Add PyUnstable_Object_IsUniqueReferencedTemporary() to determine if an object is a unique temporary object on the interpreter’s operand stack. This can be used in some cases as a replacement for checking if Py_REFCNT() is 1 for Python objects passed as arguments to C API functions. (Contributed by Sam Gross in gh-133164.)

Limited C API changes¶

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

• Remove the PySequence_Fast_GET_SIZE, PySequence_Fast_GET_ITEM, and PySequence_Fast_ITEMS macros from the limited C API, since they have always been broken in the limited C API. (Contributed by Victor Stinner in gh-91417.)

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¶

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

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

• Non-tuple sequences are now deprecated as argument for the (items) format unit in PyArg_ParseTuple() and other argument parsing functions if items contains format units which store a borrowed buffer or a borrowed reference. (Contributed by Serhiy Storchaka in gh-50333.)

• The _PyMonitoring_FireBranchEvent function is now deprecated and should be replaced with calls to PyMonitoring_FireBranchLeftEvent() and PyMonitoring_FireBranchRightEvent().

• The previously undocumented function PySequence_In() is now soft deprecated. Use PySequence_Contains() instead. (Contributed by Yuki Kobayashi in gh-127896.)