Other Language Changes

* Add:ref:`support for the perf profiler<perf_profiling>` through the new

environment variable:envvar:`PYTHONPERFSUPPORT`

and command-line option:option:`-X perf <-X>`,

as well as the new:func:`sys.activate_stack_trampoline`,

:func:`sys.deactivate_stack_trampoline`,

and:func:`sys.is_stack_trampoline_active` functions.

(Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes

with contributions from Gregory P. Smith [Google] and Mark Shannon

in:gh:`96123`.)

* The extraction methods in:mod:`tarfile`, and:func:`shutil.unpack_archive`,

have a new a *filter* argument that allows limiting tar features than may be

surprising or dangerous, such as creating files outside the destination

directory.

See:ref:`tarfile extraction filters<tarfile-extraction-filter>` for details.

In Python 3.14, the default will switch to ``'data'``.

(Contributed by Petr Viktorin in:pep:`706`.)

*:class:`types.MappingProxyType` instances are now hashable if the underlying

mapping is hashable.

(Contributed by Serhiy Storchaka in:gh:`87995`.)

*:class:`memoryview` now supports the half-float type (the "e" format code).

(Contributed by Donghee Na and Antoine Pitrou in:gh:`90751`.)

* The parser now raises:exc:`SyntaxError` when parsing source code containing

null bytes. (Contributed by Pablo Galindo in:gh:`96670`.)

*:func:`ast.parse` now raises:exc:`SyntaxError` instead of:exc:`ValueError`

when parsing source code containing null bytes. (Contributed by Pablo Galindo

in:gh:`96670`.)

* The Garbage Collector now runs only on the eval breaker mechanism of the

Python bytecode evaluation loop instead of object allocations. The GC can

also run when:c:func:`PyErr_CheckSignals` is called so C extensions that

need to run for a long time without executing any Python code also have a

chance to execute the GC periodically. (Contributed by Pablo Galindo in

:gh:`97922`.)

* A backslash-character pair that is not a valid escape sequence now generates

a:exc:`SyntaxWarning`, instead of:exc:`DeprecationWarning`.

For example, ``re.compile("\d+\.\d+")`` now emits a:exc:`SyntaxWarning`

In a future Python version they will be eventually a:exc:`SyntaxError`.

(Contributed by Victor Stinner in:gh:`98401`.)

* All builtin and extension callables expecting boolean parameters now accept

arguments of any type instead of just:class:`bool` and:class:`int`.

(Contributed by Serhiy Storchaka in:gh:`60203`.)

* Variables used in the target part of comprehensions that are not stored to

can now be used in assignment expressions (``:=``).

For example, in ``[(b := 1) for a, b.prop in some_iter]``, the assignment to

``b`` is now allowed. Note that assigning to variables stored to in the target

part of comprehensions (like ``a``) is still disallowed, as per:pep:`572`.

(Contributed by Nikita Sobolev in:gh:`100581`.)

*:class:`slice` objects are now hashable, allowing them to be used as dict keys and

set items. (Contributed by Will Bradshaw, Furkan Onder, and Raymond Hettinger in:gh:`101264`.)

*:func:`sum` now uses Neumaier summation to improve accuracy when summing

floats or mixed ints and floats.

(Contributed by Raymond Hettinger in:gh:`100425`.)

* Exceptions raised in a class or type's ``__set_name__`` method are no longer

wrapped by a:exc:`RuntimeError`. Context information is added to the

exception as a:pep:`678` note. (Contributed by Irit Katriel in:gh:`77757`.)

:exc:`ExceptionGroup`. Also changed in version 3.11.4. (Contributed by Irit

Katriel in:gh:`103590`.)

* The Garbage Collector now runs only on the eval breaker mechanism of the

Python bytecode evaluation loop instead of object allocations. The GC can

also run when:c:func:`PyErr_CheckSignals` is called so C extensions that

need to run for a long time without executing any Python code also have a

chance to execute the GC periodically. (Contributed by Pablo Galindo in

:gh:`97922`.)

* All builtin and extension callables expecting boolean parameters now accept

arguments of any type instead of just:class:`bool` and:class:`int`.

(Contributed by Serhiy Storchaka in:gh:`60203`.)

*:class:`memoryview` now supports the half-float type (the "e" format code).

(Contributed by Donghee Na and Antoine Pitrou in:gh:`90751`.)

*:class:`slice` objects are now hashable, allowing them to be used as dict keys and

set items. (Contributed by Will Bradshaw, Furkan Onder, and Raymond Hettinger in:gh:`101264`.)

*:func:`sum` now uses Neumaier summation to improve accuracy and commutativity

when summing floats or mixed ints and floats.

(Contributed by Raymond Hettinger in:gh:`100425`.)

*:func:`ast.parse` now raises:exc:`SyntaxError` instead of:exc:`ValueError`

when parsing source code containing null bytes. (Contributed by Pablo Galindo

in:gh:`96670`.)

* The extraction methods in:mod:`tarfile`, and:func:`shutil.unpack_archive`,

have a new a *filter* argument that allows limiting tar features than may be

surprising or dangerous, such as creating files outside the destination

directory.

See:ref:`tarfile extraction filters<tarfile-extraction-filter>` for details.

In Python 3.14, the default will switch to ``'data'``.

(Contributed by Petr Viktorin in:pep:`706`.)

*:class:`types.MappingProxyType` instances are now hashable if the underlying

mapping is hashable.

(Contributed by Serhiy Storchaka in:gh:`87995`.)

* Add:ref:`support for the perf profiler<perf_profiling>` through the new

environment variable:envvar:`PYTHONPERFSUPPORT`

and command-line option:option:`-X perf <-X>`,

as well as the new:func:`sys.activate_stack_trampoline`,

:func:`sys.deactivate_stack_trampoline`,

and:func:`sys.is_stack_trampoline_active` functions.

(Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes

with contributions from Gregory P. Smith [Google] and Mark Shannon

in:gh:`96123`.)

New Modules