PEP 695: Type Parameter Syntax¶

Generic classes and functions under PEP 484 were declared using a verbose syntax that left the scope of type parameters unclear and required explicit declarations of variance.

PEP 695 introduces a new, more compact and explicit way to create generic classes and functions:

def max[T](args: Iterable[T]) -> T:
    ...

class list[T]:
    def __getitem__(self, index: int, /) -> T:
        ...

    def append(self, element: T) -> None:
        ...

In addition, the PEP introduces a new way to declare type aliases using the type statement, which creates an instance of TypeAliasType:

type Point = tuple[float, float]

Type aliases can also be generic:

type Point[T] = tuple[T, T]

The new syntax allows declaring TypeVarTuple and ParamSpec parameters, as well as TypeVar parameters with bounds or constraints:

type IntFunc[**P] = Callable[P, int]  # ParamSpec
type LabeledTuple[*Ts] = tuple[str, *Ts]  # TypeVarTuple
type HashableSequence[T: Hashable] = Sequence[T]  # TypeVar with bound
type IntOrStrSequence[T: (int, str)] = Sequence[T]  # TypeVar with constraints

The value of type aliases and the bound and constraints of type variables created through this syntax are evaluated only on demand (see lazy evaluation). This means type aliases are able to refer to other types defined later in the file.

Type parameters declared through a type parameter list are visible within the scope of the declaration and any nested scopes, but not in the outer scope. For example, they can be used in the type annotations for the methods of a generic class or in the class body. However, they cannot be used in the module scope after the class is defined. See Type parameter lists for a detailed description of the runtime semantics of type parameters.

In order to support these scoping semantics, a new kind of scope is introduced, the annotation scope. Annotation scopes behave for the most part like function scopes, but interact differently with enclosing class scopes. In Python 3.13, annotations will also be evaluated in annotation scopes.

See PEP 695 for more details.

(PEP written by Eric Traut. Implementation by Jelle Zijlstra, Eric Traut, and others in gh-103764.)

PEP 701: Syntactic formalization of f-strings¶

PEP 701 lifts some restrictions on the usage of f-strings. Expression components inside f-strings can now be any valid Python expression, including strings reusing the same quote as the containing f-string, multi-line expressions, comments, backslashes, and unicode escape sequences. Let’s cover these in detail:

• Quote reuse: in Python 3.11, reusing the same quotes as the enclosing f-string raises a SyntaxError, forcing the user to either use other available quotes (like using double quotes or triple quotes if the f-string uses single quotes). In Python 3.12, you can now do things like this:

  >>> songs = ['Take me back to Eden', 'Alkaline', 'Ascensionism']
  >>> f"This is the playlist: {", ".join(songs)}"
  'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'
  

  Note that before this change there was no explicit limit in how f-strings can be nested, but the fact that string quotes cannot be reused inside the expression component of f-strings made it impossible to nest f-strings arbitrarily. In fact, this is the most nested f-string that could be written:

  >>> f"""{f'''{f'{f"{1+1}"}'}'''}"""
  '2'
  

  As now f-strings can contain any valid Python expression inside expression components, it is now possible to nest f-strings arbitrarily:

  >>> f"{f"{f"{f"{f"{f"{1+1}"}"}"}"}"}"
  '2'
  

• Multi-line expressions and comments: In Python 3.11, f-string expressions must be defined in a single line, even if the expression within the f-string could normally span multiple lines (like literal lists being defined over multiple lines), making them harder to read. In Python 3.12 you can now define f-strings spanning multiple lines, and add inline comments:

  >>> f"This is the playlist: {", ".join([
  ...     'Take me back to Eden',  # My, my, those eyes like fire
  ...     'Alkaline',              # Not acid nor alkaline
  ...     'Ascensionism'           # Take to the broken skies at last
  ... ])}"
  'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'
  

• Backslashes and unicode characters: before Python 3.12 f-string expressions couldn’t contain any \ character. This also affected unicode escape sequences (such as \N{snowman}) as these contain the \N part that previously could not be part of expression components of f-strings. Now, you can define expressions like this:

  >>> print(f"This is the playlist: {"\n".join(songs)}")
  This is the playlist: Take me back to Eden
  Alkaline
  Ascensionism
  >>> print(f"This is the playlist: {"\N{BLACK HEART SUIT}".join(songs)}")
  This is the playlist: Take me back to Eden♥Alkaline♥Ascensionism
  

See PEP 701 for more details.

As a positive side-effect of how this feature has been implemented (by parsing f-strings with the PEG parser), now error messages for f-strings are more precise and include the exact location of the error. For example, in Python 3.11, the following f-string raises a SyntaxError:

>>> my_string = f"{x z y}" + f"{1 + 1}"
  File "<stdin>", line 1
    (x z y)
     ^^^
SyntaxError: f-string: invalid syntax. Perhaps you forgot a comma?

but the error message doesn’t include the exact location of the error within the line and also has the expression artificially surrounded by parentheses. In Python 3.12, as f-strings are parsed with the PEG parser, error messages can be more precise and show the entire line:

>>> my_string = f"{x z y}" + f"{1 + 1}"
  File "<stdin>", line 1
    my_string = f"{x z y}" + f"{1 + 1}"
                   ^^^
SyntaxError: invalid syntax. Perhaps you forgot a comma?

(Contributed by Pablo Galindo, Batuhan Taskaya, Lysandros Nikolaou, Cristián Maureira-Fredes and Marta Gómez in gh-102856. PEP written by Pablo Galindo, Batuhan Taskaya, Lysandros Nikolaou and Marta Gómez).

PEP 684: A Per-Interpreter GIL¶

PEP 684 introduces a per-interpreter GIL, so that sub-interpreters may now be created with a unique GIL per interpreter. This allows Python programs to take full advantage of multiple CPU cores. This is currently only available through the C-API, though a Python API is anticipated for 3.13.

Use the new Py_NewInterpreterFromConfig() function to create an interpreter with its own GIL:

PyInterpreterConfig config = {
    .check_multi_interp_extensions = 1,
    .gil = PyInterpreterConfig_OWN_GIL,
};
PyThreadState *tstate = NULL;
PyStatus status = Py_NewInterpreterFromConfig(&tstate, &config);
if (PyStatus_Exception(status)) {
    return -1;
}
/* The new interpreter is now active in the current thread. */

For further examples how to use the C-API for sub-interpreters with a per-interpreter GIL, see Modules/_xxsubinterpretersmodule.c.

(Contributed by Eric Snow in gh-104210, etc.)

PEP 669: Low impact monitoring for CPython¶

PEP 669 defines a new API for profilers, debuggers, and other tools to monitor events in CPython. It covers a wide range of events, including calls, returns, lines, exceptions, jumps, and more. This means that you only pay for what you use, providing support for near-zero overhead debuggers and coverage tools. See sys.monitoring for details.

(Contributed by Mark Shannon in gh-103082.)

PEP 688: Making the buffer protocol accessible in Python¶

PEP 688 introduces a way to use the buffer protocol from Python code. Classes that implement the __buffer__() method are now usable as buffer types.

The new collections.abc.Buffer ABC provides a standard way to represent buffer objects, for example in type annotations. The new inspect.BufferFlags enum represents the flags that can be used to customize buffer creation. (Contributed by Jelle Zijlstra in gh-102500.)

PEP 709: Comprehension inlining¶

Dictionary, list, and set comprehensions are now inlined, rather than creating a new single-use function object for each execution of the comprehension. This speeds up execution of a comprehension by up to two times. See PEP 709 for further details.

Comprehension iteration variables remain isolated and don’t overwrite a variable of the same name in the outer scope, nor are they visible after the comprehension. Inlining does result in a few visible behavior changes:

• There is no longer a separate frame for the comprehension in tracebacks, and tracing/profiling no longer shows the comprehension as a function call.

• The symtable module will no longer produce child symbol tables for each comprehension; instead, the comprehension’s locals will be included in the parent function’s symbol table.

• Calling locals() inside a comprehension now includes variables from outside the comprehension, and no longer includes the synthetic .0 variable for the comprehension “argument”.

• A comprehension iterating directly over locals() (e.g. [k for k in locals()]) may see “RuntimeError: dictionary changed size during iteration” when run under tracing (e.g. code coverage measurement). This is the same behavior already seen in e.g. for k in locals():. To avoid the error, first create a list of keys to iterate over: keys = list(locals()); [k for k in keys].

(Contributed by Carl Meyer and Vladimir Matveev in PEP 709.)

Improved Error Messages¶

• Modules from the standard library are now potentially suggested as part of the error messages displayed by the interpreter when a NameError is raised to the top level. (Contributed by Pablo Galindo in gh-98254.)

  >>> sys.version_info
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  NameError: name 'sys' is not defined. Did you forget to import 'sys'?
  

• Improve the error suggestion for NameError exceptions for instances. Now if a NameError is raised in a method and the instance has an attribute that’s exactly equal to the name in the exception, the suggestion will include self.<NAME> instead of the closest match in the method scope. (Contributed by Pablo Galindo in gh-99139.)

  >>> class A:
  ...    def __init__(self):
  ...        self.blech = 1
  ...
  ...    def foo(self):
  ...        somethin = blech
  ...
  >>> A().foo()
  Traceback (most recent call last):
    File "<stdin>", line 1
      somethin = blech
                 ^^^^^
  NameError: name 'blech' is not defined. Did you mean: 'self.blech'?
  

• Improve the SyntaxError error message when the user types import x from y instead of from y import x. (Contributed by Pablo Galindo in gh-98931.)

  >>> import a.y.z from b.y.z
  Traceback (most recent call last):
    File "<stdin>", line 1
      import a.y.z from b.y.z
      ^^^^^^^^^^^^^^^^^^^^^^^
  SyntaxError: Did you mean to use 'from ... import ...' instead?
  

• ImportError exceptions raised from failed from <module> import <name> statements now include suggestions for the value of <name> based on the available names in <module>. (Contributed by Pablo Galindo in gh-91058.)

  >>> from collections import chainmap
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  ImportError: cannot import name 'chainmap' from 'collections'. Did you mean: 'ChainMap'?
  

PEP 692: Using TypedDict for more precise **kwargs typing¶

Typing **kwargs in a function signature as introduced by PEP 484 allowed for valid annotations only in cases where all of the **kwargs were of the same type.

PEP 692 specifies a more precise way of typing **kwargs by relying on typed dictionaries:

from typing import TypedDict, Unpack

class Movie(TypedDict):
  name: str
  year: int

def foo(**kwargs: Unpack[Movie]): ...

See PEP 692 for more details.

(Contributed by Franek Magiera in gh-103629.)

PEP 698: Override Decorator for Static Typing¶

A new decorator typing.override() has been added to the typing module. It indicates to type checkers that the method is intended to override a method in a superclass. This allows type checkers to catch mistakes where a method that is intended to override something in a base class does not in fact do so.

Example:

from typing import override

class Base:
  def get_color(self) -> str:
    return "blue"

class GoodChild(Base):
  @override  # ok: overrides Base.get_color
  def get_color(self) -> str:
    return "yellow"

class BadChild(Base):
  @override  # type checker error: does not override Base.get_color
  def get_colour(self) -> str:
    return "red"

See PEP 698 for more details.

(Contributed by Steven Troxler in gh-101561.)

array¶

• The array.array class now supports subscripting, making it a generic type. (Contributed by Jelle Zijlstra in gh-98658.)

asyncio¶

• The performance of writing to sockets in asyncio has been significantly improved. asyncio now avoids unnecessary copying when writing to sockets and uses sendmsg() if the platform supports it. (Contributed by Kumar Aditya in gh-91166.)

• Add asyncio.eager_task_factory() and asyncio.create_eager_task_factory() functions to allow opting an event loop in to eager task execution, making some use-cases 2x to 5x faster. (Contributed by Jacob Bower & Itamar Oren in gh-102853, gh-104140, and gh-104138)

• On Linux, asyncio uses asyncio.PidfdChildWatcher by default if os.pidfd_open() is available and functional instead of asyncio.ThreadedChildWatcher. (Contributed by Kumar Aditya in gh-98024.)

• The event loop now uses the best available child watcher for each platform (asyncio.PidfdChildWatcher if supported and asyncio.ThreadedChildWatcher otherwise), so manually configuring a child watcher is not recommended. (Contributed by Kumar Aditya in gh-94597.)

• Add loop_factory parameter to asyncio.run() to allow specifying a custom event loop factory. (Contributed by Kumar Aditya in gh-99388.)

• Add C implementation of asyncio.current_task() for 4x-6x speedup. (Contributed by Itamar Oren and Pranav Thulasiram Bhat in gh-100344.)

• asyncio.iscoroutine() now returns False for generators as asyncio does not support legacy generator-based coroutines. (Contributed by Kumar Aditya in gh-102748.)

• asyncio.wait() and asyncio.as_completed() now accepts generators yielding tasks. (Contributed by Kumar Aditya in gh-78530.)

calendar¶

• Add enums calendar.Month and calendar.Day defining months of the year and days of the week. (Contributed by Prince Roshan in gh-103636.)

csv¶

• Add csv.QUOTE_NOTNULL and csv.QUOTE_STRINGS flags to provide finer grained control of None and empty strings by csv.writer objects.

dis¶

• Pseudo instruction opcodes (which are used by the compiler but do not appear in executable bytecode) are now exposed in the dis module. HAVE_ARGUMENT is still relevant to real opcodes, but it is not useful for pseudo instructions. Use the new dis.hasarg collection instead. (Contributed by Irit Katriel in gh-94216.)

• Add the dis.hasexc collection to signify instructions that set an exception handler. (Contributed by Irit Katriel in gh-94216.)

fractions¶

• Objects of type fractions.Fraction now support float-style formatting. (Contributed by Mark Dickinson in gh-100161.)

importlib.resources¶

• importlib.resources.as_file() now supports resource directories. (Contributed by Jason R. Coombs in gh-97930.)

• Rename first parameter of importlib.resources.files() to anchor. (Contributed by Jason R. Coombs in gh-100598.)

inspect¶

• Add inspect.markcoroutinefunction() to mark sync functions that return a coroutine for use with inspect.iscoroutinefunction(). (Contributed by Carlton Gibson in gh-99247.)

• Add inspect.getasyncgenstate() and inspect.getasyncgenlocals() for determining the current state of asynchronous generators. (Contributed by Thomas Krennwallner in gh-79940.)

• The performance of inspect.getattr_static() has been considerably improved. Most calls to the function should be at least 2x faster than they were in Python 3.11. (Contributed by Alex Waygood in gh-103193.)

itertools¶

• Add itertools.batched() for collecting into even-sized tuples where the last batch may be shorter than the rest. (Contributed by Raymond Hettinger in gh-98363.)

math¶

• Add math.sumprod() for computing a sum of products. (Contributed by Raymond Hettinger in gh-100485.)

• Extend math.nextafter() to include a steps argument for moving up or down multiple steps at a time. (Contributed by Matthias Goergens, Mark Dickinson, and Raymond Hettinger in gh-94906.)

os¶

• Add os.PIDFD_NONBLOCK to open a file descriptor for a process with os.pidfd_open() in non-blocking mode. (Contributed by Kumar Aditya in gh-93312.)

• os.DirEntry now includes an os.DirEntry.is_junction() method to check if the entry is a junction. (Contributed by Charles Machalow in gh-99547.)

• Add os.listdrives(), os.listvolumes() and os.listmounts() functions on Windows for enumerating drives, volumes and mount points. (Contributed by Steve Dower in gh-102519.)

• os.stat() and os.lstat() are now more accurate on Windows. The st_birthtime field will now be filled with the creation time of the file, and st_ctime is deprecated but still contains the creation time (but in the future will return the last metadata change, for consistency with other platforms). st_dev may be up to 64 bits and st_ino up to 128 bits depending on your file system, and st_rdev is always set to zero rather than incorrect values. Both functions may be significantly faster on newer releases of Windows. (Contributed by Steve Dower in gh-99726.)

• As of 3.12.4, os.mkdir() and os.makedirs() on Windows now support passing a mode value of 0o700 to apply access control to the new directory. This implicitly affects tempfile.mkdtemp() and is a mitigation for CVE 2024-4030. Other values for mode continue to be ignored. (Contributed by Steve Dower in gh-118486.)

os.path¶

• Add os.path.isjunction() to check if a given path is a junction. (Contributed by Charles Machalow in gh-99547.)

• Add os.path.splitroot() to split a path into a triad (drive, root, tail). (Contributed by Barney Gale in gh-101000.)

pathlib¶

• Add support for subclassing pathlib.PurePath and pathlib.Path, plus their Posix- and Windows-specific variants. Subclasses may override the pathlib.PurePath.with_segments() method to pass information between path instances.

• Add pathlib.Path.walk() for walking the directory trees and generating all file or directory names within them, similar to os.walk(). (Contributed by Stanislav Zmiev in gh-90385.)

• Add walk_up optional parameter to pathlib.PurePath.relative_to() to allow the insertion of .. entries in the result; this behavior is more consistent with os.path.relpath(). (Contributed by Domenico Ragusa in gh-84538.)

• Add pathlib.Path.is_junction() as a proxy to os.path.isjunction(). (Contributed by Charles Machalow in gh-99547.)

• Add case_sensitive optional parameter to pathlib.Path.glob(), pathlib.Path.rglob() and pathlib.PurePath.match() for matching the path’s case sensitivity, allowing for more precise control over the matching process.

platform¶

• Add support for detecting Windows 11 and Windows Server releases past 2012. Previously, lookups on Windows Server platforms newer than Windows Server 2012 and on Windows 11 would return Windows-10. (Contributed by Steve Dower in gh-89545.)

pdb¶

• Add convenience variables to hold values temporarily for debug session and provide quick access to values like the current frame or the return value. (Contributed by Tian Gao in gh-103693.)

random¶

• Add random.binomialvariate(). (Contributed by Raymond Hettinger in gh-81620.)

• Add a default of lambd=1.0 to random.expovariate(). (Contributed by Raymond Hettinger in gh-100234.)

shutil¶

• shutil.make_archive() now passes the root_dir argument to custom archivers which support it. In this case it no longer temporarily changes the current working directory of the process to root_dir to perform archiving. (Contributed by Serhiy Storchaka in gh-74696.)

• shutil.rmtree() now accepts a new argument onexc which is an error handler like onerror but which expects an exception instance rather than a (typ, val, tb) triplet. onerror is deprecated. (Contributed by Irit Katriel in gh-102828.)

• shutil.which() now consults the PATHEXT environment variable to find matches within PATH on Windows even when the given cmd includes a directory component. (Contributed by Charles Machalow in gh-103179.)

  shutil.which() will call NeedCurrentDirectoryForExePathW when querying for executables on Windows to determine if the current working directory should be prepended to the search path. (Contributed by Charles Machalow in gh-103179.)

  shutil.which() will return a path matching the cmd with a component from PATHEXT prior to a direct match elsewhere in the search path on Windows. (Contributed by Charles Machalow in gh-103179.)

sqlite3¶

• Add a command-line interface. (Contributed by Erlend E. Aasland in gh-77617.)

• Add the sqlite3.Connection.autocommit attribute to sqlite3.Connection and the autocommit parameter to sqlite3.connect() to control PEP 249-compliant transaction handling. (Contributed by Erlend E. Aasland in gh-83638.)

• Add entrypoint keyword-only parameter to sqlite3.Connection.load_extension(), for overriding the SQLite extension entry point. (Contributed by Erlend E. Aasland in gh-103015.)

• Add sqlite3.Connection.getconfig() and sqlite3.Connection.setconfig() to sqlite3.Connection to make configuration changes to a database connection. (Contributed by Erlend E. Aasland in gh-103489.)

statistics¶

• Extend statistics.correlation() to include as a ranked method for computing the Spearman correlation of ranked data. (Contributed by Raymond Hettinger in gh-95861.)

sys¶

• Add the sys.monitoring namespace to expose the new PEP 669 monitoring API. (Contributed by Mark Shannon in gh-103082.)

• Add sys.activate_stack_trampoline() and sys.deactivate_stack_trampoline() for activating and deactivating stack profiler trampolines, and sys.is_stack_trampoline_active() for querying if stack profiler trampolines are active. (Contributed by Pablo Galindo and Christian Heimes with contributions from Gregory P. Smith [Google] and Mark Shannon in gh-96123.)

• Add sys.last_exc which holds the last unhandled exception that was raised (for post-mortem debugging use cases). Deprecate the three fields that have the same information in its legacy form: sys.last_type, sys.last_value and sys.last_traceback. (Contributed by Irit Katriel in gh-102778.)

• sys._current_exceptions() now returns a mapping from thread-id to an exception instance, rather than to a (typ, exc, tb) tuple. (Contributed by Irit Katriel in gh-103176.)

• sys.setrecursionlimit() and sys.getrecursionlimit(). The recursion limit now applies only to Python code. Builtin functions do not use the recursion limit, but are protected by a different mechanism that prevents recursion from causing a virtual machine crash.

tempfile¶

• The tempfile.NamedTemporaryFile function has a new optional parameter delete_on_close (Contributed by Evgeny Zorin in gh-58451.)

• tempfile.mkdtemp() now always returns an absolute path, even if the argument provided to the dir parameter is a relative path.

• As of 3.12.4 on Windows, the default mode 0o700 used by tempfile.mkdtemp() now limits access to the new directory due to changes to os.mkdir(). This is a mitigation for CVE 2024-4030. (Contributed by Steve Dower in gh-118486.)

threading¶

• Add threading.settrace_all_threads() and threading.setprofile_all_threads() that allow to set tracing and profiling functions in all running threads in addition to the calling one. (Contributed by Pablo Galindo in gh-93503.)

tkinter¶

• tkinter.Canvas.coords() now flattens its arguments. It now accepts not only coordinates as separate arguments (x1, y1, x2, y2, ...) and a sequence of coordinates ([x1, y1, x2, y2, ...]), but also coordinates grouped in pairs ((x1, y1), (x2, y2), ... and [(x1, y1), (x2, y2), ...]), like create_*() methods. (Contributed by Serhiy Storchaka in gh-94473.)

tokenize¶

• The tokenize module includes the changes introduced in PEP 701. (Contributed by Marta Gómez Macías and Pablo Galindo in gh-102856.) See Porting to Python 3.12 for more information on the changes to the tokenize module.

types¶

• Add types.get_original_bases() to allow for further introspection of User-defined generic types when subclassed. (Contributed by James Hilton-Balfe and Alex Waygood in gh-101827.)

typing¶

• isinstance() checks against runtime-checkable protocols now use inspect.getattr_static() rather than hasattr() to lookup whether attributes exist. This means that descriptors and __getattr__() methods are no longer unexpectedly evaluated during isinstance() checks against runtime-checkable protocols. However, it may also mean that some objects which used to be considered instances of a runtime-checkable protocol may no longer be considered instances of that protocol on Python 3.12+, and vice versa. Most users are unlikely to be affected by this change. (Contributed by Alex Waygood in gh-102433.)

• The members of a runtime-checkable protocol are now considered “frozen” at runtime as soon as the class has been created. Monkey-patching attributes onto a runtime-checkable protocol will still work, but will have no impact on isinstance() checks comparing objects to the protocol. For example:

  >>> from typing import Protocol, runtime_checkable
  >>> @runtime_checkable
  ... class HasX(Protocol):
  ...     x = 1
  ...
  >>> class Foo: ...
  ...
  >>> f = Foo()
  >>> isinstance(f, HasX)
  False
  >>> f.x = 1
  >>> isinstance(f, HasX)
  True
  >>> HasX.y = 2
  >>> isinstance(f, HasX)  # unchanged, even though HasX now also has a "y" attribute
  True
  

  This change was made in order to speed up isinstance() checks against runtime-checkable protocols.

• The performance profile of isinstance() checks against runtime-checkable protocols has changed significantly. Most isinstance() checks against protocols with only a few members should be at least 2x faster than in 3.11, and some may be 20x faster or more. However, isinstance() checks against protocols with many members may be slower than in Python 3.11. (Contributed by Alex Waygood in gh-74690 and gh-103193.)

• All typing.TypedDict and typing.NamedTuple classes now have the __orig_bases__ attribute. (Contributed by Adrian Garcia Badaracco in gh-103699.)

• Add frozen_default parameter to typing.dataclass_transform(). (Contributed by Erik De Bonte in gh-99957.)

unicodedata¶

• The Unicode database has been updated to version 15.0.0. (Contributed by Benjamin Peterson in gh-96734).

unittest¶

Add a --durations command line option, showing the N slowest test cases:

python3 -m unittest --durations=3 lib.tests.test_threading
.....
Slowest test durations
----------------------------------------------------------------------
1.210s     test_timeout (Lib.test.test_threading.BarrierTests)
1.003s     test_default_timeout (Lib.test.test_threading.BarrierTests)
0.518s     test_timeout (Lib.test.test_threading.EventTests)

(0.000 durations hidden.  Use -v to show these durations.)
----------------------------------------------------------------------
Ran 158 tests in 9.869s

OK (skipped=3)

(Contributed by Giampaolo Rodola in gh-48330)

uuid¶

• Add a command-line interface. (Contributed by Adam Chhina in gh-88597.)

Pending Removal in Python 3.13¶

Modules (see PEP 594):

• aifc

• audioop

• cgi

• cgitb

• chunk

• crypt

• imghdr

• mailcap

• msilib

• nis

• nntplib

• ossaudiodev

• pipes

• sndhdr

• spwd

• sunau

• telnetlib

• uu

• xdrlib

Other modules:

• lib2to3, and the 2to3 program (gh-84540)

APIs:

• configparser.LegacyInterpolation (gh-90765)

• locale.resetlocale() (gh-90817)

• turtle.RawTurtle.settiltangle() (gh-50096)

• unittest.findTestCases() (gh-50096)

• unittest.getTestCaseNames() (gh-50096)

• unittest.makeSuite() (gh-50096)

• unittest.TestProgram.usageExit() (gh-67048)

• webbrowser.MacOSX (gh-86421)

• classmethod descriptor chaining (gh-89519)

• importlib.resources deprecated methods:

  • contents()

  • is_resource()

  • open_binary()

  • open_text()

  • path()

  • read_binary()

  • read_text()

  Use importlib.resources.files() instead. Refer to importlib-resources: Migrating from Legacy (gh-106531)

Pending Removal in Python 3.14¶

• argparse: The type, choices, and metavar parameters of argparse.BooleanOptionalAction are deprecated and will be removed in 3.14. (Contributed by Nikita Sobolev in gh-92248.)

• ast: The following features have been deprecated in documentation since Python 3.8, now cause a DeprecationWarning to be emitted at runtime when they are accessed or used, and will be removed in Python 3.14:

  • ast.Num

  • ast.Str

  • ast.Bytes

  • ast.NameConstant

  • ast.Ellipsis

  Use ast.Constant instead. (Contributed by Serhiy Storchaka in gh-90953.)

• asyncio:

  • The child watcher classes MultiLoopChildWatcher, FastChildWatcher, AbstractChildWatcher and SafeChildWatcher are deprecated and will be removed in Python 3.14. (Contributed by Kumar Aditya in gh-94597.)

  • asyncio.set_child_watcher(), asyncio.get_child_watcher(), asyncio.AbstractEventLoopPolicy.set_child_watcher() and asyncio.AbstractEventLoopPolicy.get_child_watcher() are deprecated and will be removed in Python 3.14. (Contributed by Kumar Aditya in gh-94597.)

  • The get_event_loop() method of the default event loop policy now emits a DeprecationWarning if there is no current event loop set and it decides to create one. (Contributed by Serhiy Storchaka and Guido van Rossum in gh-100160.)

• collections.abc: Deprecated ByteString. Prefer Sequence or Buffer. For use in typing, prefer a union, like bytes | bytearray, or collections.abc.Buffer. (Contributed by Shantanu Jain in gh-91896.)

• email: Deprecated the isdst parameter in email.utils.localtime(). (Contributed by Alan Williams in gh-72346.)

• importlib: __package__ and __cached__ will cease to be set or taken into consideration by the import system (gh-97879).

• importlib.abc deprecated classes:

  • importlib.abc.ResourceReader

  • importlib.abc.Traversable

  • importlib.abc.TraversableResources

  Use importlib.resources.abc classes instead:

  • importlib.resources.abc.Traversable

  • importlib.resources.abc.TraversableResources

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

• itertools had undocumented, inefficient, historically buggy, and inconsistent support for copy, deepcopy, and pickle operations. This will be removed in 3.14 for a significant reduction in code volume and maintenance burden. (Contributed by Raymond Hettinger in gh-101588.)

• multiprocessing: The default start method will change to a safer one on Linux, BSDs, and other non-macOS POSIX platforms where 'fork' is currently the default (gh-84559). Adding a runtime warning about this was deemed too disruptive as the majority of code is not expected to care. Use the get_context() or set_start_method() APIs to explicitly specify when your code requires 'fork'. See Contexts and start methods.

• pathlib: is_relative_to() and relative_to(): passing additional arguments is deprecated.

• pkgutil: find_loader() and get_loader() now raise DeprecationWarning; use importlib.util.find_spec() instead. (Contributed by Nikita Sobolev in gh-97850.)

• pty:

  • master_open(): use pty.openpty().

  • slave_open(): use pty.openpty().

• sqlite3:

  • version and version_info.

  • execute() and executemany() if named placeholders are used and parameters is a sequence instead of a dict.

• typing: ByteString, deprecated since Python 3.9, now causes a DeprecationWarning to be emitted when it is used.

• urllib: urllib.parse.Quoter is deprecated: it was not intended to be a public API. (Contributed by Gregory P. Smith in gh-88168.)

Pending Removal in Python 3.15¶

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

• importlib:

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

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

• pathlib: pathlib.PurePath.is_reserved() is deprecated and scheduled for removal in Python 3.15. From Python 3.13 onwards, use os.path.isreserved to detect reserved paths on Windows.

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

• sysconfig:

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

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

• typing.NamedTuple:

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

• 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:

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

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

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

Pending Removal in Python 3.16¶

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

• builtins: ~bool, bitwise inversion on bool.

• symtable: Deprecate symtable.Class.get_methods() due to the lack of interest. (Contributed by Bénédikt Tran in gh-119698.)

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.

• array’s 'u' format code (gh-57281)

• builtins:

  • bool(NotImplemented).

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

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

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

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

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

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

  • 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.)

• 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.

• 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).

• unittest.IsolatedAsyncioTestCase: it is deprecated to return a value that is not None from a test case.

• urllib.parse deprecated functions: urlparse() instead

  • splitattr()

  • splithost()

  • splitnport()

  • splitpasswd()

  • splitport()

  • splitquery()

  • splittag()

  • splittype()

  • splituser()

  • splitvalue()

  • to_bytes()

• urllib.request: URLopener and FancyURLopener style of invoking requests is deprecated. Use newer urlopen() functions and methods.

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

• 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.

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

asynchat and asyncore¶

• These two modules have been removed according to the schedule in PEP 594, having been deprecated in Python 3.6. Use asyncio instead. (Contributed by Nikita Sobolev in gh-96580.)

configparser¶

• Several names deprecated in the configparser way back in 3.2 have been removed per gh-89336:

  • configparser.ParsingError no longer has a filename attribute or argument. Use the source attribute and argument instead.

  • configparser no longer has a SafeConfigParser class. Use the shorter ConfigParser name instead.

  • configparser.ConfigParser no longer has a readfp method. Use read_file() instead.

distutils¶

• Remove the distutils package. It was deprecated in Python 3.10 by PEP 632 “Deprecate distutils module”. For projects still using distutils and cannot be updated to something else, the setuptools project can be installed: it still provides distutils. (Contributed by Victor Stinner in gh-92584.)

ensurepip¶

• Remove the bundled setuptools wheel from ensurepip, and stop installing setuptools in environments created by venv.

  pip (>= 22.1) does not require setuptools to be installed in the environment. setuptools-based (and distutils-based) packages can still be used with pip install, since pip will provide setuptools in the build environment it uses for building a package.

  easy_install, pkg_resources, setuptools and distutils are no longer provided by default in environments created with venv or bootstrapped with ensurepip, since they are part of the setuptools package. For projects relying on these at runtime, the setuptools project should be declared as a dependency and installed separately (typically, using pip).

  (Contributed by Pradyun Gedam in gh-95299.)

enum¶

• Remove enum’s EnumMeta.__getattr__, which is no longer needed for enum attribute access. (Contributed by Ethan Furman in gh-95083.)

ftplib¶

• Remove ftplib’s FTP_TLS.ssl_version class attribute: use the context parameter instead. (Contributed by Victor Stinner in gh-94172.)

gzip¶

• Remove the filename attribute of gzip’s gzip.GzipFile, deprecated since Python 2.6, use the name attribute instead. In write mode, the filename attribute added '.gz' file extension if it was not present. (Contributed by Victor Stinner in gh-94196.)

hashlib¶

• Remove the pure Python implementation of hashlib’s hashlib.pbkdf2_hmac(), deprecated in Python 3.10. Python 3.10 and newer requires OpenSSL 1.1.1 (PEP 644): this OpenSSL version provides a C implementation of pbkdf2_hmac() which is faster. (Contributed by Victor Stinner in gh-94199.)

importlib¶

• Many previously deprecated cleanups in importlib have now been completed:

  • References to, and support for module_repr() has been removed. (Contributed by Barry Warsaw in gh-97850.)

  • importlib.util.set_package, importlib.util.set_loader and importlib.util.module_for_loader have all been removed. (Contributed by Brett Cannon and Nikita Sobolev in gh-65961 and gh-97850.)

  • Support for find_loader() and find_module() APIs have been removed. (Contributed by Barry Warsaw in gh-98040.)

  • importlib.abc.Finder, pkgutil.ImpImporter, and pkgutil.ImpLoader have been removed. (Contributed by Barry Warsaw in gh-98040.)

imp¶

• The imp module has been removed. (Contributed by Barry Warsaw in gh-98040.)

  To migrate, consult the following correspondence table:

  imp	importlib
  imp.NullImporter	Insert None into sys.path_importer_cache
  imp.cache_from_source()	importlib.util.cache_from_source()
  imp.find_module()	importlib.util.find_spec()
  imp.get_magic()	importlib.util.MAGIC_NUMBER
  imp.get_suffixes()	importlib.machinery.SOURCE_SUFFIXES, importlib.machinery.EXTENSION_SUFFIXES, and importlib.machinery.BYTECODE_SUFFIXES
  imp.get_tag()	sys.implementation.cache_tag
  imp.load_module()	importlib.import_module()
  imp.new_module(name)	types.ModuleType(name)
  imp.reload()	importlib.reload()
  imp.source_from_cache()	importlib.util.source_from_cache()
  imp.load_source()	See below

  Replace imp.load_source() with:

  import importlib.util
  import importlib.machinery
  
  def load_source(modname, filename):
      loader = importlib.machinery.SourceFileLoader(modname, filename)
      spec = importlib.util.spec_from_file_location(modname, filename, loader=loader)
      module = importlib.util.module_from_spec(spec)
      # The module is always executed and not cached in sys.modules.
      # Uncomment the following line to cache the module.
      # sys.modules[module.__name__] = module
      loader.exec_module(module)
      return module
  

• Remove imp functions and attributes with no replacements:

  • Undocumented functions:

    • imp.init_builtin()

    • imp.load_compiled()

    • imp.load_dynamic()

    • imp.load_package()

  • imp.lock_held(), imp.acquire_lock(), imp.release_lock(): the locking scheme has changed in Python 3.3 to per-module locks.

  • imp.find_module() constants: SEARCH_ERROR, PY_SOURCE, PY_COMPILED, C_EXTENSION, PY_RESOURCE, PKG_DIRECTORY, C_BUILTIN, PY_FROZEN, PY_CODERESOURCE, IMP_HOOK.

io¶

• Remove io’s io.OpenWrapper and _pyio.OpenWrapper, deprecated in Python 3.10: just use open() instead. The open() (io.open()) function is a built-in function. Since Python 3.10, _pyio.open() is also a static method. (Contributed by Victor Stinner in gh-94169.)

locale¶

• Remove locale’s locale.format() function, deprecated in Python 3.7: use locale.format_string() instead. (Contributed by Victor Stinner in gh-94226.)

smtpd¶

• The smtpd module has been removed according to the schedule in PEP 594, having been deprecated in Python 3.4.7 and 3.5.4. Use the aiosmtpd PyPI module or any other asyncio-based server instead. (Contributed by Oleg Iarygin in gh-93243.)

sqlite3¶

• The following undocumented sqlite3 features, deprecated in Python 3.10, are now removed:

  • sqlite3.enable_shared_cache()

  • sqlite3.OptimizedUnicode

  If a shared cache must be used, open the database in URI mode using the cache=shared query parameter.

  The sqlite3.OptimizedUnicode text factory has been an alias for str since Python 3.3. Code that previously set the text factory to OptimizedUnicode can either use str explicitly, or rely on the default value which is also str.

  (Contributed by Erlend E. Aasland in gh-92548.)

ssl¶

• Remove ssl’s ssl.RAND_pseudo_bytes() function, deprecated in Python 3.6: use os.urandom() or ssl.RAND_bytes() instead. (Contributed by Victor Stinner in gh-94199.)

• Remove the ssl.match_hostname() function. It was deprecated in Python 3.7. OpenSSL performs hostname matching since Python 3.7, Python no longer uses the ssl.match_hostname() function. (Contributed by Victor Stinner in gh-94199.)

• Remove the ssl.wrap_socket() function, deprecated in Python 3.7: instead, create a ssl.SSLContext object and call its ssl.SSLContext.wrap_socket method. Any package that still uses ssl.wrap_socket() is broken and insecure. The function neither sends a SNI TLS extension nor validates the server hostname. Code is subject to CWE 295 (Improper Certificate Validation). (Contributed by Victor Stinner in gh-94199.)

unittest¶

• Remove many long-deprecated unittest features:

  • A number of TestCase method aliases:

    Deprecated alias	Method Name	Deprecated in
    failUnless	assertTrue()	3.1
    failIf	assertFalse()	3.1
    failUnlessEqual	assertEqual()	3.1
    failIfEqual	assertNotEqual()	3.1
    failUnlessAlmostEqual	assertAlmostEqual()	3.1
    failIfAlmostEqual	assertNotAlmostEqual()	3.1
    failUnlessRaises	assertRaises()	3.1
    assert_	assertTrue()	3.2
    assertEquals	assertEqual()	3.2
    assertNotEquals	assertNotEqual()	3.2
    assertAlmostEquals	assertAlmostEqual()	3.2
    assertNotAlmostEquals	assertNotAlmostEqual()	3.2
    assertRegexpMatches	assertRegex()	3.2
    assertRaisesRegexp	assertRaisesRegex()	3.2
    assertNotRegexpMatches	assertNotRegex()	3.5

    You can use https://github.com/isidentical/teyit to automatically modernise your unit tests.

  • Undocumented and broken TestCase method assertDictContainsSubset (deprecated in Python 3.2).

  • Undocumented TestLoader.loadTestsFromModule parameter use_load_tests (deprecated and ignored since Python 3.5).

  • An alias of the TextTestResult class: _TextTestResult (deprecated in Python 3.2).

  (Contributed by Serhiy Storchaka in gh-89325.)

webbrowser¶

• Remove support for obsolete browsers from webbrowser. The removed browsers include: Grail, Mosaic, Netscape, Galeon, Skipstone, Iceape, Firebird, and Firefox versions 35 and below (gh-102871).

xml.etree.ElementTree¶

• Remove the ElementTree.Element.copy() method of the pure Python implementation, deprecated in Python 3.10, use the copy.copy() function instead. The C implementation of xml.etree.ElementTree has no copy() method, only a __copy__() method. (Contributed by Victor Stinner in gh-94383.)

zipimport¶

• Remove zipimport’s find_loader() and find_module() methods, deprecated in Python 3.10: use the find_spec() method instead. See PEP 451 for the rationale. (Contributed by Victor Stinner in gh-94379.)

Others¶

• Remove the suspicious rule from the documentation Makefile and Doc/tools/rstlint.py, both in favor of sphinx-lint. (Contributed by Julien Palard in gh-98179.)

• Remove the keyfile and certfile parameters from the ftplib, imaplib, poplib and smtplib modules, and the key_file, cert_file and check_hostname parameters from the http.client module, all deprecated since Python 3.6. Use the context parameter (ssl_context in imaplib) instead. (Contributed by Victor Stinner in gh-94172.)

• Remove Jython compatibility hacks from several stdlib modules and tests. (Contributed by Nikita Sobolev in gh-99482.)

• Remove _use_broken_old_ctypes_structure_semantics_ flag from ctypes module. (Contributed by Nikita Sobolev in gh-99285.)

Changes in the Python API¶

• 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.)

• Remove randrange() functionality deprecated since Python 3.10. Formerly, randrange(10.0) losslessly converted to randrange(10). Now, it raises a TypeError. Also, the exception raised for non-integer values such as randrange(10.5) or randrange('10') has been changed from ValueError to TypeError. This also prevents bugs where randrange(1e25) would silently select from a larger range than randrange(10**25). (Originally suggested by Serhiy Storchaka gh-86388.)

• argparse.ArgumentParser changed encoding and error handler for reading arguments from file (e.g. fromfile_prefix_chars option) from default text encoding (e.g. locale.getpreferredencoding(False)) to filesystem encoding and error handler. Argument files should be encoded in UTF-8 instead of ANSI Codepage on Windows.

• Remove the asyncore-based smtpd module deprecated in Python 3.4.7 and 3.5.4. A recommended replacement is the asyncio-based aiosmtpd PyPI module.

• shlex.split(): Passing None for s argument now raises an exception, rather than reading sys.stdin. The feature was deprecated in Python 3.9. (Contributed by Victor Stinner in gh-94352.)

• The os module no longer accepts bytes-like paths, like bytearray and memoryview types: only the exact bytes type is accepted for bytes strings. (Contributed by Victor Stinner in gh-98393.)

• syslog.openlog() and syslog.closelog() now fail if used in subinterpreters. syslog.syslog() may still be used in subinterpreters, but now only if syslog.openlog() has already been called in the main interpreter. These new restrictions do not apply to the main interpreter, so only a very small set of users might be affected. This change helps with interpreter isolation. Furthermore, syslog is a wrapper around process-global resources, which are best managed from the main interpreter. (Contributed by Donghee Na in gh-99127.)

• The undocumented locking behavior of cached_property() is removed, because it locked across all instances of the class, leading to high lock contention. This means that a cached property getter function could now run more than once for a single instance, if two threads race. For most simple cached properties (e.g. those that are idempotent and simply calculate a value based on other attributes of the instance) this will be fine. If synchronization is needed, implement locking within the cached property getter function or around multi-threaded access points.

• sys._current_exceptions() now returns a mapping from thread-id to an exception instance, rather than to a (typ, exc, tb) tuple. (Contributed by Irit Katriel in gh-103176.)

• When extracting tar files using tarfile or shutil.unpack_archive(), pass the filter argument to limit features that may be surprising or dangerous. See Extraction filters for details.

• The output of the tokenize.tokenize() and tokenize.generate_tokens() functions is now changed due to the changes introduced in PEP 701. This means that STRING tokens are not emitted any more for f-strings and the tokens described in PEP 701 are now produced instead: FSTRING_START, FSTRING_MIDDLE and FSTRING_END are now emitted for f-string “string” parts in addition to the appropriate tokens for the tokenization in the expression components. For example for the f-string f"start {1+1} end" the old version of the tokenizer emitted:

  1,0-1,18:           STRING         'f"start {1+1} end"'
  

  while the new version emits:

  1,0-1,2:            FSTRING_START  'f"'
  1,2-1,8:            FSTRING_MIDDLE 'start '
  1,8-1,9:            OP             '{'
  1,9-1,10:           NUMBER         '1'
  1,10-1,11:          OP             '+'
  1,11-1,12:          NUMBER         '1'
  1,12-1,13:          OP             '}'
  1,13-1,17:          FSTRING_MIDDLE ' end'
  1,17-1,18:          FSTRING_END    '"'
  

  Additionally, there may be some minor behavioral changes as a consequence of the changes required to support PEP 701. Some of these changes include:

  • The type attribute of the tokens emitted when tokenizing some invalid Python characters such as ! has changed from ERRORTOKEN to OP.

  • Incomplete single-line strings now also raise tokenize.TokenError as incomplete multiline strings do.

  • Some incomplete or invalid Python code now raises tokenize.TokenError instead of returning arbitrary ERRORTOKEN tokens when tokenizing it.

  • Mixing tabs and spaces as indentation in the same file is not supported anymore and will raise a TabError.

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

  Any library or application that provides a custom _thread module should provide _is_main_interpreter(). (See gh-112826.)

New Features¶

• PEP 697: Introduce the Unstable C API tier, intended for low-level tools like debuggers and JIT compilers. This API may change in each minor release of CPython without deprecation warnings. Its contents are marked by the PyUnstable_ prefix in names.

  Code object constructors:

  • PyUnstable_Code_New() (renamed from PyCode_New)

  • PyUnstable_Code_NewWithPosOnlyArgs() (renamed from PyCode_NewWithPosOnlyArgs)

  Extra storage for code objects (PEP 523):

  • PyUnstable_Eval_RequestCodeExtraIndex() (renamed from _PyEval_RequestCodeExtraIndex)

  • PyUnstable_Code_GetExtra() (renamed from _PyCode_GetExtra)

  • PyUnstable_Code_SetExtra() (renamed from _PyCode_SetExtra)

  The original names will continue to be available until the respective API changes.

  (Contributed by Petr Viktorin in gh-101101.)

• PEP 697: Add an API for extending types whose instance memory layout is opaque:

  • PyType_Spec.basicsize can be zero or negative to specify inheriting or extending the base class size.

  • PyObject_GetTypeData() and PyType_GetTypeDataSize() added to allow access to subclass-specific instance data.

  • Py_TPFLAGS_ITEMS_AT_END and PyObject_GetItemData() added to allow safely extending certain variable-sized types, including PyType_Type.

  • Py_RELATIVE_OFFSET added to allow defining members in terms of a subclass-specific struct.

  (Contributed by Petr Viktorin in gh-103509.)

• Add the new limited C API function PyType_FromMetaclass(), which generalizes the existing PyType_FromModuleAndSpec() using an additional metaclass argument. (Contributed by Wenzel Jakob in gh-93012.)

• API for creating objects that can be called using the vectorcall protocol was added to the Limited API:

  • Py_TPFLAGS_HAVE_VECTORCALL

  • PyVectorcall_NARGS()

  • PyVectorcall_Call()

  • vectorcallfunc

  The Py_TPFLAGS_HAVE_VECTORCALL flag is now removed from a class when the class’s __call__() method is reassigned. This makes vectorcall safe to use with mutable types (i.e. heap types without the immutable flag, Py_TPFLAGS_IMMUTABLETYPE). Mutable types that do not override tp_call now inherit the Py_TPFLAGS_HAVE_VECTORCALL flag. (Contributed by Petr Viktorin in gh-93274.)

  The Py_TPFLAGS_MANAGED_DICT and Py_TPFLAGS_MANAGED_WEAKREF flags have been added. This allows extensions classes to support object __dict__ and weakrefs with less bookkeeping, using less memory and with faster access.

• API for performing calls using the vectorcall protocol was added to the Limited API:

  • PyObject_Vectorcall()

  • PyObject_VectorcallMethod()

  • PY_VECTORCALL_ARGUMENTS_OFFSET

  This means that both the incoming and outgoing ends of the vector call protocol are now available in the Limited API. (Contributed by Wenzel Jakob in gh-98586.)

• Add two new public functions, PyEval_SetProfileAllThreads() and PyEval_SetTraceAllThreads(), that allow to set tracing and profiling functions in all running threads in addition to the calling one. (Contributed by Pablo Galindo in gh-93503.)

• Add new function PyFunction_SetVectorcall() to the C API which sets the vectorcall field of a given PyFunctionObject. (Contributed by Andrew Frost in gh-92257.)

• The C API now permits registering callbacks via PyDict_AddWatcher(), PyDict_Watch() and related APIs to be called whenever a dictionary is modified. This is intended for use by optimizing interpreters, JIT compilers, or debuggers. (Contributed by Carl Meyer in gh-91052.)

• Add PyType_AddWatcher() and PyType_Watch() API to register callbacks to receive notification on changes to a type. (Contributed by Carl Meyer in gh-91051.)

• Add PyCode_AddWatcher() and PyCode_ClearWatcher() APIs to register callbacks to receive notification on creation and destruction of code objects. (Contributed by Itamar Oren in gh-91054.)

• Add PyFrame_GetVar() and PyFrame_GetVarString() functions to get a frame variable by its name. (Contributed by Victor Stinner in gh-91248.)

• Add PyErr_GetRaisedException() and PyErr_SetRaisedException() for saving and restoring the current exception. These functions return and accept a single exception object, rather than the triple arguments of the now-deprecated PyErr_Fetch() and PyErr_Restore(). This is less error prone and a bit more efficient. (Contributed by Mark Shannon in gh-101578.)

• Add _PyErr_ChainExceptions1, which takes an exception instance, to replace the legacy-API _PyErr_ChainExceptions, which is now deprecated. (Contributed by Mark Shannon in gh-101578.)

• Add PyException_GetArgs() and PyException_SetArgs() as convenience functions for retrieving and modifying the args passed to the exception’s constructor. (Contributed by Mark Shannon in gh-101578.)

• Add PyErr_DisplayException(), which takes an exception instance, to replace the legacy-api PyErr_Display(). (Contributed by Irit Katriel in gh-102755).

• PEP 683: Introduce Immortal Objects, which allows objects to bypass reference counts, and related changes to the C-API:

  • _Py_IMMORTAL_REFCNT: The reference count that defines an object

    as immortal.

  • _Py_IsImmortal Checks if an object has the immortal reference count.

  • PyObject_HEAD_INIT This will now initialize reference count to

    _Py_IMMORTAL_REFCNT when used with Py_BUILD_CORE.

  • SSTATE_INTERNED_IMMORTAL An identifier for interned unicode objects

    that are immortal.

  • SSTATE_INTERNED_IMMORTAL_STATIC An identifier for interned unicode

    objects that are immortal and static

  • sys.getunicodeinternedsize This returns the total number of unicode

    objects that have been interned. This is now needed for refleak.py to correctly track reference counts and allocated blocks

  (Contributed by Eddie Elizondo in gh-84436.)

• PEP 684: Add the new Py_NewInterpreterFromConfig() function and PyInterpreterConfig, which may be used to create sub-interpreters with their own GILs. (See PEP 684: A Per-Interpreter GIL for more info.) (Contributed by Eric Snow in gh-104110.)

• In the limited C API version 3.12, Py_INCREF() and Py_DECREF() functions are now implemented as opaque function calls to hide implementation details. (Contributed by Victor Stinner in gh-105387.)

Porting to Python 3.12¶

• Legacy Unicode APIs based on Py_UNICODE* representation has been removed. Please migrate to APIs based on UTF-8 or wchar_t*.

• Argument parsing functions like PyArg_ParseTuple() doesn’t support Py_UNICODE* based format (e.g. u, Z) anymore. Please migrate to other formats for Unicode like s, z, es, and U.

• tp_weaklist for all static builtin types is always NULL. This is an internal-only field on PyTypeObject but we’re pointing out the change in case someone happens to be accessing the field directly anyway. To avoid breakage, consider using the existing public C-API instead, or, if necessary, the (internal-only) _PyObject_GET_WEAKREFS_LISTPTR() macro.

• This internal-only PyTypeObject.tp_subclasses may now not be a valid object pointer. Its type was changed to void* to reflect this. We mention this in case someone happens to be accessing the internal-only field directly.

  To get a list of subclasses, call the Python method __subclasses__() (using PyObject_CallMethod(), for example).

• Add support of more formatting options (left aligning, octals, uppercase hexadecimals, intmax_t, ptrdiff_t, wchar_t C strings, variable width and precision) in PyUnicode_FromFormat() and PyUnicode_FromFormatV(). (Contributed by Serhiy Storchaka in gh-98836.)

• An unrecognized format character in PyUnicode_FromFormat() and PyUnicode_FromFormatV() now sets a SystemError. In previous versions it caused all the rest of the format string to be copied as-is to the result string, and any extra arguments discarded. (Contributed by Serhiy Storchaka in gh-95781.)

• Fix wrong sign placement in PyUnicode_FromFormat() and PyUnicode_FromFormatV(). (Contributed by Philip Georgi in gh-95504.)

• Extension classes wanting to add a __dict__ or weak reference slot should use Py_TPFLAGS_MANAGED_DICT and Py_TPFLAGS_MANAGED_WEAKREF instead of tp_dictoffset and tp_weaklistoffset, respectively. The use of tp_dictoffset and tp_weaklistoffset is still supported, but does not fully support multiple inheritance (gh-95589), and performance may be worse. Classes declaring Py_TPFLAGS_MANAGED_DICT should call _PyObject_VisitManagedDict() and _PyObject_ClearManagedDict() to traverse and clear their instance’s dictionaries. To clear weakrefs, call PyObject_ClearWeakRefs(), as before.

• The PyUnicode_FSDecoder() function no longer accepts bytes-like paths, like bytearray and memoryview types: only the exact bytes type is accepted for bytes strings. (Contributed by Victor Stinner in gh-98393.)

• The Py_CLEAR, Py_SETREF and Py_XSETREF macros now only evaluate their arguments once. If an argument has side effects, these side effects are no longer duplicated. (Contributed by Victor Stinner in gh-98724.)

• The interpreter’s error indicator is now always normalized. This means that PyErr_SetObject(), PyErr_SetString() and the other functions that set the error indicator now normalize the exception before storing it. (Contributed by Mark Shannon in gh-101578.)

• _Py_RefTotal is no longer authoritative and only kept around for ABI compatibility. Note that it is an internal global and only available on debug builds. If you happen to be using it then you’ll need to start using _Py_GetGlobalRefTotal().

• The following functions now select an appropriate metaclass for the newly created type:

  • PyType_FromSpec()

  • PyType_FromSpecWithBases()

  • PyType_FromModuleAndSpec()

  Creating classes whose metaclass overrides tp_new is deprecated, and in Python 3.14+ it will be disallowed. Note that these functions ignore tp_new of the metaclass, possibly allowing incomplete initialization.

  Note that PyType_FromMetaclass() (added in Python 3.12) already disallows creating classes whose metaclass overrides tp_new (__new__() in Python).

  Since tp_new overrides almost everything PyType_From* functions do, the two are incompatible with each other. The existing behavior – ignoring the metaclass for several steps of type creation – is unsafe in general, since (meta)classes assume that tp_new was called. There is no simple general workaround. One of the following may work for you:

  • If you control the metaclass, avoid using tp_new in it:

    • If initialization can be skipped, it can be done in tp_init instead.

    • If the metaclass doesn’t need to be instantiated from Python, set its tp_new to NULL using the Py_TPFLAGS_DISALLOW_INSTANTIATION flag. This makes it acceptable for PyType_From* functions.

  • Avoid PyType_From* functions: if you don’t need C-specific features (slots or setting the instance size), create types by calling the metaclass.

  • If you know the tp_new can be skipped safely, filter the deprecation warning out using warnings.catch_warnings() from Python.

• PyOS_InputHook and PyOS_ReadlineFunctionPointer are no longer called in subinterpreters. This is because clients generally rely on process-wide global state (since these callbacks have no way of recovering extension module state).

  This also avoids situations where extensions may find themselves running in a subinterpreter that they don’t support (or haven’t yet been loaded in). See gh-104668 for more info.

• PyLongObject has had its internals changed for better performance. Although the internals of PyLongObject are private, they are used by some extension modules. The internal fields should no longer be accessed directly, instead the API functions beginning PyLong_... should be used instead. Two new unstable API functions are provided for efficient access to the value of PyLongObjects which fit into a single machine word:

  • PyUnstable_Long_IsCompact()

  • PyUnstable_Long_CompactValue()

• Custom allocators, set via PyMem_SetAllocator(), are now required to be thread-safe, regardless of memory domain. Allocators that don’t have their own state, including “hooks”, are not affected. If your custom allocator is not already thread-safe and you need guidance then please create a new GitHub issue and CC @ericsnowcurrently.

Deprecated¶

• In accordance with PEP 699, the ma_version_tag field in PyDictObject is deprecated for extension modules. Accessing this field will generate a compiler warning at compile time. This field will be removed in Python 3.14. (Contributed by Ramvikrams and Kumar Aditya in gh-101193. PEP by Ken Jin.)

• Deprecate global configuration variable:

  • Py_DebugFlag: use PyConfig.parser_debug

  • Py_VerboseFlag: use PyConfig.verbose

  • Py_QuietFlag: use PyConfig.quiet

  • Py_InteractiveFlag: use PyConfig.interactive

  • Py_InspectFlag: use PyConfig.inspect

  • Py_OptimizeFlag: use PyConfig.optimization_level

  • Py_NoSiteFlag: use PyConfig.site_import

  • Py_BytesWarningFlag: use PyConfig.bytes_warning

  • Py_FrozenFlag: use PyConfig.pathconfig_warnings

  • Py_IgnoreEnvironmentFlag: use PyConfig.use_environment

  • Py_DontWriteBytecodeFlag: use PyConfig.write_bytecode

  • Py_NoUserSiteDirectory: use PyConfig.user_site_directory

  • Py_UnbufferedStdioFlag: use PyConfig.buffered_stdio

  • Py_HashRandomizationFlag: use PyConfig.use_hash_seed and PyConfig.hash_seed

  • Py_IsolatedFlag: use PyConfig.isolated

  • Py_LegacyWindowsFSEncodingFlag: use PyPreConfig.legacy_windows_fs_encoding

  • Py_LegacyWindowsStdioFlag: use PyConfig.legacy_windows_stdio

  • Py_FileSystemDefaultEncoding: use PyConfig.filesystem_encoding

  • Py_HasFileSystemDefaultEncoding: use PyConfig.filesystem_encoding

  • Py_FileSystemDefaultEncodeErrors: use PyConfig.filesystem_errors

  • Py_UTF8Mode: use PyPreConfig.utf8_mode (see Py_PreInitialize())

  The Py_InitializeFromConfig() API should be used with PyConfig instead. (Contributed by Victor Stinner in gh-77782.)

• Creating immutable types with mutable bases is deprecated and will be disabled in Python 3.14. (gh-95388)

• The structmember.h header is deprecated, though it continues to be available and there are no plans to remove it.

  Its contents are now available just by including Python.h, with a Py prefix added if it was missing:

  • PyMemberDef, PyMember_GetOne() and PyMember_SetOne()

  • Type macros like Py_T_INT, Py_T_DOUBLE, etc. (previously T_INT, T_DOUBLE, etc.)

  • The flags Py_READONLY (previously READONLY) and Py_AUDIT_READ (previously all uppercase)

  Several items are not exposed from Python.h:

  • T_OBJECT (use Py_T_OBJECT_EX)

  • T_NONE (previously undocumented, and pretty quirky)

  • The macro WRITE_RESTRICTED which does nothing.

  • The macros RESTRICTED and READ_RESTRICTED, equivalents of Py_AUDIT_READ.

  • In some configurations, <stddef.h> is not included from Python.h. It should be included manually when using offsetof().

  The deprecated header continues to provide its original contents under the original names. Your old code can stay unchanged, unless the extra include and non-namespaced macros bother you greatly.

  (Contributed in gh-47146 by Petr Viktorin, based on earlier work by Alexander Belopolsky and Matthias Braun.)

• PyErr_Fetch() and PyErr_Restore() are deprecated. Use PyErr_GetRaisedException() and PyErr_SetRaisedException() instead. (Contributed by Mark Shannon in gh-101578.)

• PyErr_Display() is deprecated. Use PyErr_DisplayException() instead. (Contributed by Irit Katriel in gh-102755).

• _PyErr_ChainExceptions is deprecated. Use _PyErr_ChainExceptions1 instead. (Contributed by Irit Katriel in gh-102192.)

• Using PyType_FromSpec(), PyType_FromSpecWithBases() or PyType_FromModuleAndSpec() to create a class whose metaclass overrides tp_new is deprecated. Call the metaclass instead.

Removed¶

• Remove the token.h header file. There was never any public tokenizer C API. The token.h header file was only designed to be used by Python internals. (Contributed by Victor Stinner in gh-92651.)

• Legacy Unicode APIs have been removed. See PEP 623 for detail.

  • PyUnicode_WCHAR_KIND

  • PyUnicode_AS_UNICODE()

  • PyUnicode_AsUnicode()

  • PyUnicode_AsUnicodeAndSize()

  • PyUnicode_AS_DATA()

  • PyUnicode_FromUnicode()

  • PyUnicode_GET_SIZE()

  • PyUnicode_GetSize()

  • PyUnicode_GET_DATA_SIZE()

• Remove the PyUnicode_InternImmortal() function macro. (Contributed by Victor Stinner in gh-85858.)

ipaddress¶

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

email¶

• Headers with embedded newlines are now quoted on output.

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

email¶

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

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.

os.path¶

• The strict parameter to os.path.realpath() accepts a new value, os.path.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.)

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.)

ssl¶

• The ssl module now rejects TLS certificate chains that contain one of a set of compromised eMudhra intermediate CA certificates. The affected certificates are identified by their public key, so cross-signed copies that reuse the same key are blocked as well. It is a defense-in-depth backstop that applies even when an application supplies its own root CA bundle, and regardless of whether the platform trust store has removed trust. (Contributed by Christian Heimes in gh-160040 for CVE 2026-115557.)