Doc/whatsnew/3.15.rst
What's new in Python 3.15
:Editor: Hugo van Kemenade
.. Rules for maintenance:
Anyone can add text to this document. Do not spend very much time on the wording of your changes, because your text will probably get rewritten to some degree.
The maintainer will go through Misc/NEWS periodically and add changes; it's therefore more important to add your changes to Misc/NEWS than to this file.
This is not a complete list of every single change; completeness is the purpose of Misc/NEWS. Some changes I consider too small or esoteric to include. If such a change is added to the text, I'll just remove it. (This is another reason you shouldn't spend too much time on writing your addition.)
If you want to draw your new text to the attention of the maintainer, add 'XXX' to the beginning of the paragraph or section.
It's OK to just add a fragmentary note about a change. For example: "XXX Describe the transmogrify() function added to the socket module." The maintainer will research the change and write the necessary text.
You can comment out your additions if you like, but it's not necessary (especially when a final release is some months away).
Credit the author of a patch or bugfix. Just the name is sufficient; the e-mail address isn't necessary.
It's helpful to add the issue number as a comment:
XXX Describe the transmogrify() function added to the socket
module.
(Contributed by P.Y. Developer in :gh:12345.)
This saves the maintainer the effort of going through the VCS log when researching a change.
This article explains the new features in Python 3.15, compared to 3.14.
For full details, see the :ref:changelog <changelog>.
.. note::
Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.15 moves towards release, so it's worth checking back even after reading earlier versions.
.. This section singles out the most important changes in Python 3.15. Brevity is key.
.. PEP-sized items next.
810: :ref:Explicit lazy imports for faster startup times <whatsnew315-lazy-imports>814: :ref:Add frozendict built-in type <whatsnew315-frozendict>799: :ref:A dedicated profiling package for organizing Python profiling tools <whatsnew315-profiling-package>799: :ref:Tachyon: High frequency statistical sampling profiler <whatsnew315-sampling-profiler>798: :ref:Unpacking in comprehensions <whatsnew315-unpacking-in-comprehensions>686: :ref:Python now uses UTF-8 as the default encoding <whatsnew315-utf8-default>728: TypedDict with typed extra items747: :ref:Annotating type forms with TypeForm <whatsnew315-typeform>782: :ref:A new PyBytesWriter C API to create a Python bytes object <whatsnew315-pybyteswriter>The JIT compiler has been significantly upgraded <whatsnew315-jit>Improved error messages <whatsnew315-improved-error-messages>The official Windows 64-bit binaries now use the tail-calling interpreter <whatsnew315-windows-tail-calling-interpreter>.. _whatsnew315-lazy-imports:
810: Explicit lazy importsLarge Python applications often suffer from slow startup times. A significant contributor to this problem is the import system: when a module is imported, Python must locate the file, read it from disk, compile it to bytecode, and execute all top-level code. For applications with deep dependency trees, this process can take seconds, even when most of the imported code is never actually used during a particular run.
Developers have worked around this by moving imports inside functions, using
:mod:importlib to load modules on demand, or restructuring code to avoid
unnecessary dependencies. These approaches work but make code harder to read
and maintain, scatter import statements throughout the codebase, and require
discipline to apply consistently.
Python now provides a cleaner solution through explicit :keyword:lazy
imports using the new lazy soft keyword. When you mark an import as
lazy, Python defers the actual module loading until the imported name is
first used. This gives you the organizational benefits of declaring all
imports at the top of the file while only paying the loading cost for
modules you actually use.
The lazy keyword works with both import and from ... import
statements. When you write lazy import heavy_module, Python does not
immediately load the module. Instead, it creates a lightweight proxy object.
The actual module loading happens transparently when you first access the
name:
.. code-block:: python
lazy import json lazy from pathlib import Path
print("Starting up...") # json and pathlib not loaded yet
data = json.loads('{"key": "value"}') # json loads here p = Path(".") # pathlib loads here
This mechanism is particularly useful for applications that import many modules at the top level but may only use a subset of them in any given run. The deferred loading reduces startup latency without requiring code restructuring or conditional imports scattered throughout the codebase.
In the case where loading a lazily imported module fails (for example, if the module does not exist), Python raises the exception at the point of first use rather than at import time. The associated traceback includes both the location where the name was accessed and the original import statement, making it straightforward to diagnose & debug the failure.
For cases where you want to enable lazy loading globally without modifying
source code, Python provides the :option:-X lazy_imports <-X> command-line
option and the :envvar:PYTHON_LAZY_IMPORTS environment variable. Both
accept three values: all makes all imports lazy by default, none
disables lazy imports entirely (even explicit lazy statements become
eager), and normal (the default) respects the lazy keyword in source
code. The :func:sys.set_lazy_imports and :func:sys.get_lazy_imports
functions allow changing and querying this mode at runtime.
For more selective control, :func:sys.set_lazy_imports_filter accepts a
callable that determines whether a specific module should be loaded lazily.
The filter receives three arguments: the importing module's name (or
None), the imported module's name, and the fromlist (or None for
regular imports). It should return True to allow the import to be lazy,
or False to force eager loading. This allows patterns like making only
your own application's modules lazy while keeping third-party dependencies
eager:
.. code-block:: python
import sys
def myapp_filter(importing, imported, fromlist): return imported.startswith("myapp.") sys.set_lazy_imports_filter(myapp_filter) sys.set_lazy_imports("all")
import myapp.slow_module # lazy (matches filter) import json # eager (does not match filter)
The proxy type itself is available as :data:types.LazyImportType for code
that needs to detect lazy imports programmatically.
There are some restrictions on where the lazy keyword can be used. Lazy
imports are only permitted at module scope; using lazy inside a
function, class body, or try/except/finally block raises a
:exc:SyntaxError. Neither star imports nor future imports can be lazy
(lazy from module import * and lazy from __future__ import ... both
raise :exc:SyntaxError).
.. seealso:: :pep:810 for the full specification and rationale.
(Contributed by Pablo Galindo Salgado and Dino Viehland in :gh:142349.)
.. _whatsnew315-frozendict:
814: Add frozendict built-in typeA new :term:immutable type, :class:frozendict, is added to the :mod:builtins module.
It does not allow modification after creation. A :class:!frozendict is not a subclass of dict;
it inherits directly from object. A :class:!frozendict is :term:hashable
as long as all of its keys and values are hashable. A :class:!frozendict preserves
insertion order, but comparison does not take order into account.
For example::
>>> a = frozendict(x=1, y=2)
>>> a
frozendict({'x': 1, 'y': 2})
>>> a['z'] = 3
Traceback (most recent call last):
File "<python-input-2>", line 1, in <module>
a['z'] = 3
~^^^^^
TypeError: 'frozendict' object does not support item assignment
>>> b = frozendict(y=2, x=1)
>>> hash(a) == hash(b)
True
>>> a == b
True
The following standard library modules have been updated to accept
:class:!frozendict: :mod:copy, :mod:decimal, :mod:json, :mod:marshal,
:mod:plistlib (only for serialization), :mod:pickle, :mod:pprint and
:mod:xml.etree.ElementTree.
:func:eval and :func:exec accept :class:!frozendict for globals, and
:func:type and :meth:str.maketrans accept :class:!frozendict for dict.
Code checking for :class:dict type using isinstance(arg, dict) can be
updated to isinstance(arg, (dict, frozendict)) to accept also the
:class:!frozendict type, or to isinstance(arg, collections.abc.Mapping)
to accept also other mapping types such as :class:~types.MappingProxyType.
.. seealso:: :pep:814 for the full specification and rationale.
(Contributed by Victor Stinner and Donghee Na in :gh:141510.)
.. _whatsnew315-profiling-package:
799: A dedicated profiling packageA new :mod:profiling module has been added to organize Python's built-in
profiling tools under a single, coherent namespace. This module contains:
profiling.tracing: deterministic function-call tracing (relocated from
cProfile).profiling.sampling: a new statistical sampling profiler (named Tachyon).The cProfile module remains as an alias for backwards compatibility.
The :mod:profile module is deprecated and will be removed in Python 3.17.
.. seealso:: :pep:799 for further details.
(Contributed by Pablo Galindo and László Kiss Kollár in :gh:138122.)
.. _whatsnew315-sampling-profiler:
.. image:: ../library/tachyon-logo.png :alt: Tachyon profiler logo :align: center :width: 200px
A new statistical sampling profiler (Tachyon) has been added as
:mod:profiling.sampling. This profiler enables low-overhead performance analysis of
running Python processes without requiring code modification or process restart.
Unlike deterministic profilers (such as :mod:profiling.tracing) that instrument
every function call, the sampling profiler periodically captures stack traces from
running processes. This approach provides virtually zero overhead while achieving
sampling rates of up to 1,000,000 Hz, making it the fastest sampling profiler
available for Python (at the time of its contribution) and ideal for debugging
performance issues in production environments. This capability is particularly
valuable for debugging performance issues in production systems where traditional
profiling approaches would be too intrusive.
Key features include:
Zero-overhead profiling: Attach to any running Python process without affecting its performance. Ideal for production debugging where you can't afford to restart or slow down your application.
No code modification required: Profile existing applications without restart. Simply point the profiler at a running process by PID and start collecting data.
Flexible target modes:
attach) - attach to already-running applicationsrun) - profile from the very start of executionrun -m) - profile packages run as python -m moduleMultiple profiling modes: Choose what to measure based on your performance investigation:
--mode wall, default): Measures real elapsed time including I/O,
network waits, and blocking operations. Use this to understand where your program spends
calendar time, including when waiting for external resources.--mode cpu): Measures only active CPU execution time, excluding I/O waits
and blocking. Use this to identify CPU-bound bottlenecks and optimize computational work.--mode gil): Measures time spent holding Python's Global Interpreter
Lock. Use this to identify which threads dominate GIL usage in multi-threaded applications.--mode exception): Captures samples only from threads with
an active exception. Use this to analyze exception handling overhead.Thread-aware profiling: Option to profile all threads (-a) or just the main thread,
essential for understanding multi-threaded application behavior.
Multiple output formats: Choose the visualization that best fits your workflow:
--pstats: Detailed tabular statistics compatible with :mod:pstats. Shows function-level
timing with direct and cumulative samples. Best for detailed analysis and integration with
existing Python profiling tools.--collapsed: Generates collapsed stack traces (one line per stack). This format is
specifically designed for creating flame graphs with external tools like Brendan Gregg's
FlameGraph scripts or speedscope.--flamegraph: Generates a self-contained interactive HTML flame graph using D3.js.
Opens directly in your browser for immediate visual analysis. Flame graphs show the call
hierarchy where width represents time spent, making it easy to spot bottlenecks at a glance.--gecko: Generates Gecko Profiler format compatible with Firefox Profiler <https://profiler.firefox.com>__. Upload the output to Firefox Profiler for advanced
timeline-based analysis with features like stack charts, markers, and network activity.--heatmap: Generates an interactive HTML heatmap visualization with line-level sample
counts. Creates a directory with per-file heatmaps showing exactly where time is spent
at the source code level.Live interactive mode: Real-time TUI profiler with a top-like interface (--live).
Monitor performance as your application runs with interactive sorting and filtering.
Async-aware profiling: Profile async/await code with task-based stack reconstruction
(--async-aware). See which coroutines are consuming time, with options to show only
running tasks or all tasks including those waiting.
Opcode-level profiling: Gather bytecode opcode information for instruction-level
profiling (--opcodes). Shows which bytecode instructions are executing, including
specializations from the adaptive interpreter.
See :mod:profiling.sampling for the complete documentation, including all
available output formats, profiling modes, and configuration options.
(Contributed by Pablo Galindo and László Kiss Kollár in :gh:135953 and :gh:138122.)
.. _whatsnew315-unpacking-in-comprehensions:
798: Unpacking in ComprehensionsList, set, and dictionary comprehensions, as well as generator expressions, now
support unpacking with * and **. This extends the unpacking syntax
from :pep:448 to comprehensions, providing a new syntax for combining an
arbitrary number of iterables or dictionaries into a single flat structure.
This new syntax is a direct alternative to nested comprehensions,
:func:itertools.chain, and :meth:itertools.chain.from_iterable. For
example::
>>> lists = [[1, 2], [3, 4], [5]]
>>> [*L for L in lists] # equivalent to [x for L in lists for x in L]
[1, 2, 3, 4, 5]
>>> sets = [{1, 2}, {2, 3}, {3, 4}]
>>> {*s for s in sets} # equivalent to {x for s in sets for x in s}
{1, 2, 3, 4}
>>> dicts = [{'a': 1}, {'b': 2}, {'a': 3}]
>>> {**d for d in dicts} # equivalent to {k: v for d in dicts for k,v in d.items()}
{'a': 3, 'b': 2}
Generator expressions can similarly use unpacking to yield values from multiple iterables::
>>> gen = (*L for L in lists) # equivalent to (x for L in lists for x in L)
>>> list(gen)
[1, 2, 3, 4, 5]
This change also extends to asynchronous generator expressions, such that, for
example, (*a async for a in agen()) is equivalent to (x async for a in agen() for x in a).
.. seealso:: :pep:798 for further details.
(Contributed by Adam Hartz in :gh:143055.)
.. _whatsnew315-improved-error-messages:
The interpreter now provides more helpful suggestions in :exc:AttributeError
exceptions when accessing an attribute on an object that does not exist, but
a similar attribute is available through one of its members.
For example, if the object has an attribute that itself exposes the requested name, the error message will suggest accessing it via that inner attribute:
.. code-block:: python
@dataclass class Circle: radius: float
@property
def area(self) -> float:
return pi * self.radius**2
class Container: def init(self, inner: Circle) -> None: self.inner = inner
circle = Circle(radius=4.0) container = Container(circle) print(container.area)
Running this code now produces a clearer suggestion:
.. code-block:: pycon
Traceback (most recent call last): File "/home/pablogsal/github/python/main/lel.py", line 42, in <module> print(container.area) ^^^^^^^^^^^^^^ AttributeError: 'Container' object has no attribute 'area'. Did you mean '.inner.area' instead of '.area'?
.. _whatsnew315-utf8-default:
Python now uses UTF-8_ as the default encoding, independent of the system's
environment. This means that I/O operations without an explicit encoding,
for example, open('flying-circus.txt'), will use UTF-8.
UTF-8 is a widely-supported Unicode_ character encoding that has become a
de facto standard for representing text, including nearly every webpage
on the internet, many common file formats, programming languages, and more.
This only applies when no encoding argument is given. For best
compatibility between versions of Python, ensure that an explicit encoding
argument is always provided. The :ref:opt-in encoding warning <io-encoding-warning>
can be used to identify code that may be affected by this change.
The special encoding='locale' argument uses the current locale
encoding, and has been supported since Python 3.10.
To retain the previous behaviour, Python's UTF-8 mode may be disabled with
the :envvar:PYTHONUTF8=0 <PYTHONUTF8> environment variable or the
:option:-X utf8=0 <-X> command-line option.
.. seealso:: :pep:686 for further details.
.. _UTF-8: https://en.wikipedia.org/wiki/UTF-8 .. _Unicode: https://home.unicode.org/
(Contributed by Adam Turner in :gh:133711; PEP 686 written by Inada Naoki.)
Several error messages incorrectly using the term "argument" have been corrected.
(Contributed by Stan Ulbrych in :gh:133382.)
The interpreter now tries to provide a suggestion when
:func:delattr fails due to a missing attribute.
When an attribute name that closely resembles an existing attribute is used,
the interpreter will suggest the correct attribute name in the error message.
For example:
.. doctest::
class A: ... pass a = A() a.abcde = 1 del a.abcdf # doctest: +ELLIPSIS Traceback (most recent call last): ... AttributeError: 'A' object has no attribute 'abcdf'. Did you mean: 'abcde'?
(Contributed by Nikita Sobolev and Pranjal Prajapati in :gh:136588.)
Unraisable exceptions are now highlighted with color by default. This can be
controlled by :ref:environment variables <using-on-controlling-color>.
(Contributed by Peter Bierma in :gh:134170.)
The :meth:~object.__repr__ of :class:ImportError and :class:ModuleNotFoundError
now shows "name" and "path" as name=<name> and path=<path> if they were given
as keyword arguments at construction time.
(Contributed by Serhiy Storchaka, Oleg Iarygin, and Yoav Nir in :gh:74185.)
The :attr:~object.__dict__ and :attr:!__weakref__ descriptors now use a
single descriptor instance per interpreter, shared across all types that
need them.
This speeds up class creation, and helps avoid reference cycles.
(Contributed by Petr Viktorin in :gh:135228.)
The :option:-W option and the :envvar:PYTHONWARNINGS environment variable
can now specify regular expressions instead of literal strings to match
the warning message and the module name, if the corresponding field starts
and ends with a forward slash (/).
(Contributed by Serhiy Storchaka in :gh:134716.)
Functions that take timestamp or timeout arguments now accept any real
numbers (such as :class:~decimal.Decimal and :class:~fractions.Fraction),
not only integers or floats, although this does not improve precision.
(Contributed by Serhiy Storchaka in :gh:67795.)
.. _whatsnew315-bytearray-take-bytes:
Added :meth:bytearray.take_bytes(n=None, /) <bytearray.take_bytes> to take
bytes out of a :class:bytearray without copying. This enables optimizing code
which must return :class:bytes after working with a mutable buffer of bytes
such as data buffering, network protocol parsing, encoding, decoding,
and compression. Common code patterns which can be optimized with
:func:~bytearray.take_bytes are listed below.
.. list-table:: Suggested optimizing refactors :header-rows: 1
* - Description
- Old
- New
* - Return :class:`bytes` after working with :class:`bytearray`
- .. code:: python
def read() -> bytes:
buffer = bytearray(1024)
...
return bytes(buffer)
- .. code:: python
def read() -> bytes:
buffer = bytearray(1024)
...
return buffer.take_bytes()
* - Empty a buffer getting the bytes
- .. code:: python
buffer = bytearray(1024)
...
data = bytes(buffer)
buffer.clear()
- .. code:: python
buffer = bytearray(1024)
...
data = buffer.take_bytes()
* - Split a buffer at a specific separator
- .. code:: python
buffer = bytearray(b'abc\ndef')
n = buffer.find(b'\n')
data = bytes(buffer[:n + 1])
del buffer[:n + 1]
assert data == b'abc'
assert buffer == bytearray(b'def')
- .. code:: python
buffer = bytearray(b'abc\ndef')
n = buffer.find(b'\n')
data = buffer.take_bytes(n + 1)
* - Split a buffer at a specific separator; discard after the separator
- .. code:: python
buffer = bytearray(b'abc\ndef')
n = buffer.find(b'\n')
data = bytes(buffer[:n])
buffer.clear()
assert data == b'abc'
assert len(buffer) == 0
- .. code:: python
buffer = bytearray(b'abc\ndef')
n = buffer.find(b'\n')
buffer.resize(n)
data = buffer.take_bytes()
(Contributed by Cody Maloney in :gh:139871.)
Many functions related to compiling or parsing Python code, such as
:func:compile, :func:ast.parse, :func:symtable.symtable,
and :func:importlib.abc.InspectLoader.source_to_code, now allow the module
name to be passed. It is needed to unambiguously :ref:filter <warning-filter>
syntax warnings by module name.
(Contributed by Serhiy Storchaka in :gh:135801.)
Allowed defining the dict and weakref :ref:__slots__ <slots>
for any class.
(Contributed by Serhiy Storchaka in :gh:41779.)
Allowed defining any :ref:__slots__ <slots> for a class derived from
:class:tuple (including classes created by :func:collections.namedtuple).
(Contributed by Serhiy Storchaka in :gh:41779.)
The :class:slice type now supports subscription,
making it a :term:generic type.
(Contributed by James Hilton-Balfe in :gh:128335.)
The class :class:memoryview now supports the :c:expr:float complex and
:c:expr:double complex C types: formatting characters 'F' and 'D'
respectively.
(Contributed by Sergey B Kirpichev in :gh:146151.)
Allow the count argument of :meth:bytes.replace to be a keyword.
(Contributed by Stan Ulbrych in :gh:147856.)
This module provides access to the mathematical functions for integer
arguments (:pep:791).
(Contributed by Serhiy Storchaka in :gh:81313.)
The :class:~argparse.BooleanOptionalAction action supports now single-dash
long options and alternate prefix characters.
(Contributed by Serhiy Storchaka in :gh:138525.)
Changed the suggest_on_error parameter of :class:argparse.ArgumentParser to
default to True. This enables suggestions for mistyped arguments by default.
(Contributed by Jakob Schluse in :gh:140450.)
Added backtick markup support in description and epilog text to highlight
inline code when color output is enabled.
(Contributed by Savannah Ostrowski in :gh:142390.)
Support the :c:expr:float complex and :c:expr:double complex C types:
formatting characters 'F' and 'D' respectively.
(Contributed by Sergey B Kirpichev in :gh:146151.)
Support half-floats (16-bit IEEE 754 binary interchange format): formatting
character 'e'.
(Contributed by Sergey B Kirpichev in :gh:146238.)
Added the pad parameter in :func:~base64.z85encode.
(Contributed by Hauke Dämpfling in :gh:143103.)
Added the padded parameter in
:func:~base64.b32encode, :func:~base64.b32decode,
:func:~base64.b32hexencode, :func:~base64.b32hexdecode,
:func:~base64.b64encode, :func:~base64.b64decode,
:func:~base64.urlsafe_b64encode, and :func:~base64.urlsafe_b64decode.
(Contributed by Serhiy Storchaka in :gh:73613.)
Added the wrapcol parameter in :func:~base64.b16encode,
:func:~base64.b32encode, :func:~base64.b32hexencode,
:func:~base64.b64encode, :func:~base64.b85encode, and
:func:~base64.z85encode.
(Contributed by Serhiy Storchaka in :gh:143214 and :gh:146431.)
Added the ignorechars parameter in :func:~base64.b16decode,
:func:~base64.b32decode, :func:~base64.b32hexdecode,
:func:~base64.b64decode, :func:~base64.b85decode, and
:func:~base64.z85decode.
(Contributed by Serhiy Storchaka in :gh:144001 and :gh:146431.)
Added functions for Base32 encoding:
~binascii.b2a_base32 and :func:~binascii.a2b_base32(Contributed by James Seo in :gh:146192.)
Added functions for Ascii85, Base85, and Z85 encoding:
~binascii.b2a_ascii85 and :func:~binascii.a2b_ascii85~binascii.b2a_base85 and :func:~binascii.a2b_base85(Contributed by James Seo and Serhiy Storchaka in :gh:101178.)
Added the padded parameter in
:func:~binascii.b2a_base32, :func:~binascii.a2b_base32,
:func:~binascii.b2a_base64, and :func:~binascii.a2b_base64.
(Contributed by Serhiy Storchaka in :gh:73613.)
Added the wrapcol parameter in :func:~binascii.b2a_base64.
(Contributed by Serhiy Storchaka in :gh:143214.)
Added the alphabet parameter in :func:~binascii.b2a_base64 and
:func:~binascii.a2b_base64.
(Contributed by Serhiy Storchaka in :gh:145980.)
Added the ignorechars parameter in :func:~binascii.a2b_hex,
:func:~binascii.unhexlify, and :func:~binascii.a2b_base64.
(Contributed by Serhiy Storchaka in :gh:144001 and :gh:146431.)
Calendar pages generated by the :class:calendar.HTMLCalendar class now support
dark mode and have been migrated to the HTML5 standard for improved accessibility.
(Contributed by Jiahao Li and Hugo van Kemenade in :gh:137634.)
The :mod:calendar's :ref:command-line <calendar-cli> HTML output now
accepts the year-month option: python -m calendar -t html 2009 06.
(Contributed by Pål Grønås Drange in :gh:140212.)
!collections.Counter.__xor__ and
:meth:!collections.Counter.__ixor__ to compute the symmetric difference
between :class:~collections.Counter objects.
(Contributed by Raymond Hettinger in :gh:138682.)concurrent.futures.ProcessPoolExecutor terminates abruptly.
The resulting traceback will now tell you the PID and exit code of the
terminated process.
(Contributed by Jonathan Berg in :gh:139486.)!__enter__,
:meth:!__exit__, :meth:!__aenter__, and :meth:!__aexit__ in
:class:~contextlib.ExitStack and :class:contextlib.AsyncExitStack, for
consistency with the :keyword:with and :keyword:async with statements.
(Contributed by Serhiy Storchaka in :gh:144386.)__init__ methods no longer include internal
type names.!reorganize methods to :mod:dbm.dumb and :mod:dbm.sqlite3
which allow to recover unused free space previously occupied by deleted entries.
(Contributed by Andrea Oliveri in :gh:134004.).. _whatsnew315-color-difflib:
Introduced the optional color parameter to :func:difflib.unified_diff,
enabling color output similar to :program:git diff.
This can be controlled by :ref:environment variables <using-on-controlling-color>.
(Contributed by Douglas Thor in :gh:133725.)
Improved the styling of HTML diff pages generated by the :class:difflib.HtmlDiff
class, and migrated the output to the HTML5 standard.
(Contributed by Jiahao Li in :gh:134580.)
:func:~functools.singledispatchmethod now supports non-:term:descriptor
callables.
(Contributed by Serhiy Storchaka in :gh:140873.)
:func:~functools.singledispatchmethod now dispatches on the second argument
if it wraps a regular method and is called as a class attribute.
(Contributed by Bartosz Sławecki in :gh:143535.)
hashlib even if they will not work at runtime due to
missing backend implementations. For instance, hashlib.md5 will no
longer raise :exc:AttributeError if OpenSSL is not available and Python
has been built without MD5 support.
(Contributed by Bénédikt Tran in :gh:136929.)~http.client.HTTPConnection and :class:~http.client.HTTPSConnection
constructors. This parameter overrides the default maximum number of allowed
response headers.
(Contributed by Alexander Enrique Urieles Nieto in :gh:131724.)"' double quotes in cookie values.
(Contributed by Nick Burns and Senthil Kumaran in :gh:92936.)~inspect.getdoc.
(Contributed by Serhiy Storchaka in :gh:132686.)~json.load and
:func:~json.loads functions:
allow a callback for JSON literal array types to customize Python lists in
the resulting decoded object. Passing combined :class:frozendict to
object_pairs_hook param and :class:tuple to array_hook will yield a
deeply nested immutable Python structure representing the JSON data.
(Contributed by Joao S. O. Bueno in :gh:146440):func:~locale.setlocale now supports language codes with @-modifiers.
@-modifiers are no longer silently removed in :func:~locale.getlocale,
but included in the language code.
(Contributed by Serhiy Storchaka in :gh:137729.)
Undeprecate the :func:locale.getdefaultlocale function.
(Contributed by Victor Stinner in :gh:130796.)
Add :func:math.isnormal and :func:math.issubnormal functions.
(Contributed by Sergey B Kirpichev in :gh:132908.)
Add :func:math.fmax, :func:math.fmin and :func:math.signbit functions.
(Contributed by Bénédikt Tran in :gh:135853.)
Add application/dicom MIME type for .dcm extension.
(Contributed by Benedikt Johannes in :gh:144217.)
Add application/efi. (Contributed by Charlie Lin in :gh:145720.)
Add application/node MIME type for .cjs extension.
(Contributed by John Franey in :gh:140937.)
Add application/toml. (Contributed by Gil Forcada in :gh:139959.)
Add application/sql and application/vnd.sqlite3.
(Contributed by Charlie Lin in :gh:145698.)
Add the following MIME types:
application/vnd.ms-cab-compressed for .cab extensionapplication/vnd.ms-htmlhelp for .chm extensionapplication/vnd.ms-officetheme for .thmx extension(Contributed by Charlie Lin in :gh:145718.)
Add image/jxl. (Contributed by Foolbar in :gh:144213.)
Rename application/x-texinfo to application/texinfo.
(Contributed by Charlie Lin in :gh:140165.)
Changed the MIME type for .ai files to application/pdf.
(Contributed by Stan Ulbrych in :gh:141239.)
:class:mmap.mmap now has a trackfd parameter on Windows;
if it is False, the file handle corresponding to fileno will
not be duplicated.
(Contributed by Serhiy Storchaka in :gh:78502.)
Added the :meth:mmap.mmap.set_name method
to annotate an anonymous memory mapping
if Linux kernel supports :manpage:PR_SET_VMA_ANON_NAME <PR_SET_VMA(2const)> (Linux 5.17 or newer).
(Contributed by Donghee Na in :gh:142419.)
os.statx on Linux kernel versions 4.11 and later with
glibc versions 2.28 and later.
(Contributed by Jeffrey Bosboom and Victor Stinner in :gh:83714.)Add support of the all-but-last mode in :func:~os.path.realpath.
(Contributed by Serhiy Storchaka in :gh:71189.)
The strict parameter to :func:os.path.realpath accepts a new value,
:data:os.path.ALLOW_MISSING.
If used, errors other than :exc: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.)
77188.)re.prefixmatch and a corresponding :meth:~re.Pattern.prefixmatch
have been added as alternate more explicit names for the existing
:func:re.match and :meth:~re.Pattern.match APIs. These are intended
to be used to alleviate confusion around what match means by following the
Zen of Python's "Explicit is better than implicit" mantra. Most other
language regular expression libraries use an API named match to mean what
Python has always called search.
(Contributed by Gregory P. Smith in :gh:86519.)~resource.RLIMIT_NTHR,
:data:~resource.RLIMIT_UMTXP, :data:~resource.RLIMIT_THREADS,
:data:~resource.RLIM_SAVED_CUR, and :data:~resource.RLIM_SAVED_MAX.
(Contributed by Serhiy Storchaka in :gh:137512.)!reorganize method to :mod:shelve used to recover unused free
space previously occupied by deleted entries.
(Contributed by Andrea Oliveri in :gh:134004.)shelve module.
(Contributed by Furkan Onder in :gh:99631.)86819.)The :ref:command-line interface <sqlite3-cli> has several new features:
SQL keyword completion on <tab>.
(Contributed by Long Tan in :gh:133393.)
Prompts, error messages, and help text are now colored.
This is enabled by default, see :ref:using-on-controlling-color for
details.
(Contributed by Stan Ulbrych and Łukasz Langa in :gh:133461.)
Table, index, trigger, view, column, function, and schema completion on <tab>.
(Contributed by Long Tan in :gh:136101.)
Indicate through :data:ssl.HAS_PSK_TLS13 whether the :mod:ssl module
supports "External PSKs" in TLSv1.3, as described in :rfc:9258.
(Contributed by Will Childs-Klein in :gh:133624.)
Added new methods for managing groups used for SSL key agreement
ssl.SSLContext.set_groups sets the groups allowed for doing
key agreement, extending the previous
:meth:ssl.SSLContext.set_ecdh_curve method.
This new API provides the ability to list multiple groups and
supports fixed-field and post-quantum groups in addition to ECDH
curves. This method can also be used to control what key shares
are sent in the TLS handshake.ssl.SSLSocket.group returns the group selected for doing key
agreement on the current connection after the TLS handshake completes.
This call requires OpenSSL 3.2 or later.ssl.SSLContext.get_groups returns a list of all available key
agreement groups compatible with the minimum and maximum TLS versions
currently set in the context. This call requires OpenSSL 3.5 or later.(Contributed by Ron Frederick in :gh:136306.)
Added a new method :meth:ssl.SSLContext.set_ciphersuites for setting TLS 1.3
ciphers. For TLS 1.2 or earlier, :meth:ssl.SSLContext.set_ciphers should
continue to be used. Both calls can be made on the same context and the
selected cipher suite will depend on the TLS version negotiated when a
connection is made.
(Contributed by Ron Frederick in :gh:137197.)
Added new methods for managing signature algorithms:
ssl.get_sigalgs returns a list of all available TLS signature
algorithms. This call requires OpenSSL 3.4 or later.ssl.SSLContext.set_client_sigalgs sets the signature algorithms
allowed for certificate-based client authentication.ssl.SSLContext.set_server_sigalgs sets the signature algorithms
allowed for the server to complete the TLS handshake.ssl.SSLSocket.client_sigalg returns the signature algorithm
selected for client authentication on the current connection. This call
requires OpenSSL 3.5 or later.ssl.SSLSocket.server_sigalg returns the signature algorithm
selected for the server to complete the TLS handshake on the current
connection. This call requires OpenSSL 3.5 or later.(Contributed by Ron Frederick in :gh:138252.)
:meth:subprocess.Popen.wait: when timeout is not None and the
platform supports it, an efficient event-driven mechanism is used to wait for
process termination:
os.pidfd_open + :func:select.poll.select.kqueue + KQ_FILTER_PROC + KQ_NOTE_EXIT.WaitForSingleObject (unchanged).If none of these mechanisms are available, the function falls back to the
traditional busy loop (non-blocking call and short sleeps).
(Contributed by Giampaolo Rodola in :gh:83069).
symtable.Function.get_cells and :meth:symtable.Symbol.is_cell methods.
(Contributed by Yashp002 in :gh:143504.)sys.abi_info namespace to improve access to ABI information.
(Contributed by Klaus Zimmermann in :gh:137476.)~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.)~tarfile.TarFile.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.)~tarfile.TarFile.extract and :func:~tarfile.TarFile.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, :exc:~tarfile.LinkFallbackError.
(Contributed by Petr Viktorin for :cve:2025-4330 and :cve:2024-12718.)~tarfile.TarFile.extract and :func:~tarfile.TarFile.extractall
no longer extract rejected members when
:func:~tarfile.TarFile.errorlevel is zero.
(Contributed by Matt Prodani and Petr Viktorin in :gh:112887
and :cve:2025-4435.)~tarfile.TarFile.extract and :func:~tarfile.TarFile.extractall
now replace slashes by backslashes in symlink targets on Windows to prevent
creation of corrupted links.
(Contributed by Christoph Walcher in :gh:57911.)The command-line interface now colorizes error tracebacks
by default. This can be controlled with
:ref:environment variables <using-on-controlling-color>.
(Contributed by Yi Hong in :gh:139374.)
Make the target time of :meth:timeit.Timer.autorange configurable
and add --target-time option to the command-line interface.
(Contributed by Alessandro Cucci and Miikka Koskinen in :gh:140283.)
The :meth:!tkinter.Text.search method now supports two additional
arguments: nolinestop which allows the search to
continue across line boundaries;
and strictlimits which restricts the search to within the specified range.
(Contributed by Rihaan Meher in :gh:130848.)
A new method :meth:!tkinter.Text.search_all has been introduced.
This method allows for searching for all matches of a pattern
using Tcl's -all and -overlap options.
(Contributed by Rihaan Meher in :gh:130848.)
Added new methods :meth:!pack_content, :meth:!place_content and
:meth:!grid_content which use Tk commands with new names (introduced
in Tk 8.6) instead of :meth:!*_slaves methods which use Tk commands
with outdated names.
(Contributed by Serhiy Storchaka in :gh:143754.)
Added :class:!Event attributes :attr:!user_data for Tk virtual events
and :attr:!detail for Enter, Leave, FocusIn, FocusOut,
and ConfigureRequest events.
(Contributed by Matthias Kievernagel and Serhiy Storchaka in :gh:47655.)
.. _whatsnew315-tomllib-1-1-0:
The :mod:tomllib module now supports TOML 1.1.0.
This is a backwards compatible update, meaning that all valid TOML 1.0.0
documents are parsed the same way.
The changes, according to the official TOML changelog_, are:
Allow newlines and trailing commas in inline tables.
Previously an inline table had to be on a single line and couldn't end with a trailing comma. This is now relaxed so that the following is valid:
.. syntax highlighting needs TOML 1.1.0 support in Pygments, see https://github.com/pygments/pygments/issues/3026
.. code-block:: text
tbl = { key = "a string", moar-tbl = { key = 1, }, }
Add \xHH notation to basic strings for codepoints under 255,
and the \e escape for the escape character:
.. code-block:: text
null = "null byte: \x00; letter a: \x61" csi = "\e["
Seconds in datetime and time values are now optional. The following are now valid:
.. code-block:: text
dt = 2010-02-03 14:15 t = 14:15
(Contributed by Taneli Hukkinen in :gh:142956.)
.. _official TOML changelog: https://github.com/toml-lang/toml/blob/main/CHANGELOG.md
locals proxy type
as :data:types.FrameLocalsProxyType.
This represents the type of the :attr:frame.f_locals attribute,
as described in :pep:667... _whatsnew315-typeform:
:pep:747: Add :data:~typing.TypeForm, a new special form for annotating
values that are themselves type expressions.
TypeForm[T] means "a type form object describing T (or a type
assignable to T)". At runtime, TypeForm(x) simply returns x,
which allows explicit annotation of type-form values without changing
behavior.
This helps libraries that accept user-provided type expressions
(for example int, str | None, :class:~typing.TypedDict
classes, or list[int]) expose precise signatures:
.. code-block:: python
from typing import Any, TypeForm
def cast[T](typ: TypeForm[T], value: Any) -> T: ...
(Contributed by Jelle Zijlstra in :gh:145033.)
Code like class ExtraTypeVars(P1[S], Protocol[T, T2]): ... now raises
a :exc:TypeError, because S is not listed in Protocol parameters.
(Contributed by Nikita Sobolev in :gh:137191.)
Code like class B2(A[T2], Protocol[T1, T2]): ... now correctly handles
type parameters order: it is (T1, T2), not (T2, T1)
as it was incorrectly inferred in runtime before.
(Contributed by Nikita Sobolev in :gh:137191.)
The Unicode database has been updated to Unicode 17.0.0.
Add :func:unicodedata.isxidstart and :func:unicodedata.isxidcontinue
functions to check whether a character can start or continue a
Unicode Standard Annex #31 <https://www.unicode.org/reports/tr31/>_ identifier.
(Contributed by Stan Ulbrych in :gh:129117.)
Add the :func:~unicodedata.iter_graphemes
function to iterate over grapheme clusters according to rules defined in
Unicode Standard Annex #29, "Unicode Text Segmentation" <https://www.unicode.org/reports/tr29/>_.
Add :func:~unicodedata.grapheme_cluster_break,
:func:~unicodedata.indic_conjunct_break and
:func:~unicodedata.extended_pictographic functions to get the properties
of the character which are related to the above algorithm.
(Contributed by Serhiy Storchaka and Guillaume Sanchez in :gh:74902.)
Add :func:~unicodedata.block function to return the Unicode block <https://www.unicode.org/versions/Unicode17.0.0/core-spec/chapter-3/#G64189>_
assigned to a character.
(Contributed by Stan Ulbrych in :gh:66802.)
unittest.TestCase.assertLogs will now accept a formatter
to control how messages are formatted.
(Contributed by Garry Cairns in :gh:134567.)~urllib.parse.urlsplit,
:func:~urllib.parse.urlparse and :func:~urllib.parse.urldefrag functions.
Add the keep_empty parameter to :func:~urllib.parse.urlunsplit and
:func:~urllib.parse.urlunparse functions.
This allows to distinguish between empty and not defined URI components
and preserve empty components.
(Contributed by Serhiy Storchaka in :gh:67041.)lib64 -> lib symlink.
This means purelib and platlib of virtual environments no longer share the
same lib directory on platforms where :data:sys.platlibdir is not
equal to lib.
(Contributed by Rui Xi in :gh:133951.)warnings.warn_explicit if no module
argument is passed.
It now tests the module regular expression in the warnings filter not only
against the filename with .py stripped, but also against module names
constructed starting from different parent directories of the filename
(with /__init__.py, .py and, on Windows, .pyw stripped).
(Contributed by Serhiy Storchaka in :gh:135801.)Add :meth:~xml.parsers.expat.xmlparser.SetAllocTrackerActivationThreshold
and :meth:~xml.parsers.expat.xmlparser.SetAllocTrackerMaximumAmplification
to :ref:xmlparser <xmlparser-objects> objects to tune protections against
disproportional amounts of dynamic memory usage from within an Expat parser.
(Contributed by Bénédikt Tran in :gh:90949.)
Add :meth:~xml.parsers.expat.xmlparser.SetBillionLaughsAttackProtectionActivationThreshold
and :meth:~xml.parsers.expat.xmlparser.SetBillionLaughsAttackProtectionMaximumAmplification
to :ref:xmlparser <xmlparser-objects> objects to tune protections against
billion laughs_ attacks.
(Contributed by Bénédikt Tran in :gh:90949.)
.. _billion laughs: https://en.wikipedia.org/wiki/Billion_laughs_attack
Allow combining two Adler-32 checksums via :func:~zlib.adler32_combine.
(Contributed by Callum Attryde and Bénédikt Tran in :gh:134635.)
Allow combining two CRC-32 checksums via :func:~zlib.crc32_combine.
(Contributed by Bénédikt Tran in :gh:134635.)
.. Add improved modules above alphabetically, not here at the end.
mimalloc is now used as the default allocator for
for raw memory allocations such as via :c:func:PyMem_RawMalloc
for better performance on :term:free-threaded builds <free-threaded build>.
(Contributed by Kumar Aditya in :gh:144914.)CPython's underlying base64 implementation now encodes 2x faster and decodes 3x
faster thanks to simple CPU pipelining optimizations.
(Contributed by Gregory P. Smith and Serhiy Storchaka in :gh:143262.)
Implementation for Ascii85, Base85, and Z85 encoding has been rewritten in C.
Encoding and decoding is now two orders of magnitude faster and consumes
two orders of magnitude less memory.
(Contributed by James Seo and Serhiy Storchaka in :gh:101178.)
Implementation for Base32 has been rewritten in C.
Encoding and decoding is now two orders of magnitude faster.
(Contributed by James Seo in :gh:146192)
csv.Sniffer.sniff delimiter detection is now up to 1.6x faster.
(Contributed by Maurycy Pawłowski-Wieroński in :gh:137628.).. _whatsnew315-jit:
Results from the pyperformance <https://github.com/python/pyperformance>__
benchmark suite report
6-7% <https://www.doesjitgobrrr.com/run/2026-04-01>__
geometric mean performance improvement for the JIT over the standard CPython
interpreter built with all optimizations enabled on x86-64 Linux. On AArch64
macOS, the JIT has a
12-13% <https://www.doesjitgobrrr.com/run/2026-04-01>__
speedup over the :ref:tail calling interpreter <whatsnew314-tail-call-interpreter>
with all optimizations enabled. The speedups for JIT
builds versus no JIT builds range from roughly 15% slowdown to over
100% speedup (ignoring the unpack_sequence microbenchmark) on
x86-64 Linux and AArch64 macOS systems.
.. attention:: These results are not yet final.
The major upgrades to the JIT are:
.. rubric:: LLVM 21 build-time dependency
The JIT compiler now uses LLVM 21 for build-time stencil generation. As
always, LLVM is only needed when building CPython with the JIT enabled;
end users running Python do not need LLVM installed. Instructions for
installing LLVM can be found in the JIT compiler documentation <https://github.com/python/cpython/blob/main/Tools/jit/README.md>__
for all supported platforms.
(Contributed by Savannah Ostrowski in :gh:140973.)
.. rubric:: A new tracing frontend
The JIT compiler now supports significantly more bytecode operations and control flow than in Python 3.14, enabling speedups on a wider variety of code. For example, simple Python object creation is now understood by the 3.15 JIT compiler. Overloaded operations and generators are also partially supported. This was made possible by an overhauled JIT tracing frontend that records actual execution paths through code, rather than estimating them as the previous implementation did.
(Contributed by Ken Jin in :gh:139109. Support for Windows added by
Mark Shannon in :gh:141703.)
.. rubric:: Basic register allocation in the JIT
A basic form of register allocation has been added to the JIT compiler's optimizer. This allows the JIT compiler to avoid certain stack operations altogether and instead operate on registers. This allows the JIT to produce more efficient traces by avoiding reads and writes to memory.
(Contributed by Mark Shannon in :gh:135379.)
.. rubric:: More JIT optimizations
More constant-propagation <https://en.wikipedia.org/wiki/Constant_folding>__
is now performed. This means when the JIT compiler detects that certain user
code results in constants, the code can be simplified by the JIT.
(Contributed by Ken Jin and Savannah Ostrowski in :gh:132732.)
The JIT avoids :term:reference count\ s where possible. This generally
reduces the cost of most operations in Python.
(Contributed by Ken Jin, Donghee Na, Zheao Li, Hai Zhu, Savannah Ostrowski,
Reiden Ong, Noam Cohen, Tomas Roun, PuQing, Cajetan Rodrigues, and Sacul in :gh:134584.)
.. rubric:: Better machine code generation
The JIT compiler's machine code generator now produces better machine code for x86-64 and AArch64 macOS and Linux targets. In general, users should experience lower memory usage for generated machine code and more efficient machine code versus the old JIT.
(Contributed by Brandt Bucher in :gh:136528 and :gh:136528.
Implementation for AArch64 contributed by Mark Shannon in :gh:139855.
Additional optimizations for AArch64 contributed by Mark Shannon and
Diego Russo in :gh:140683 and :gh:142305.)
collections.abc.ByteString has been removed from
collections.abc.__all__. :class:!collections.abc.ByteString has been
deprecated since Python 3.12, and is scheduled for removal in Python 3.17.!ctypes.SetPointerType,
which has been deprecated since Python 3.13.
(Contributed by Bénédikt Tran in :gh:133866.)!glob.glob0 and :func:!glob.glob1
functions, which have been deprecated since Python 3.13. Use
:func:glob.glob and pass a directory to its root_dir argument instead.
(Contributed by Barney Gale in :gh:137466.)!CGIHTTPRequestHandler class
and the --cgi flag from the :program:python -m http.server
command-line interface. They were deprecated in Python 3.13.
(Contributed by Bénédikt Tran in :gh:133810.)package parameter
from :func:importlib.resources.files function.
(Contributed by Semyon Moroz in :gh:138044.)!pathlib.PurePath.is_reserved.
Use :func:os.path.isreserved to detect reserved paths on Windows.
(Contributed by Nikita Sobolev in :gh:133875.)!platform.java_ver function,
which was deprecated since Python 3.13.
(Contributed by Alexey Makridenko in :gh:133604.)pprint.pprint,
:func:pprint.pformat, :func:pprint.pp. If true, the output will be
formatted similar to pretty-printed :func:json.dumps when
indent is supplied.
(Contributed by Stefan Todoran and Semyon Moroz in :gh:112632.)!sre_compile, :mod:!sre_constants and :mod:!sre_parse modules.
(Contributed by Stan Ulbrych in :gh:135994.)sysconfig.is_python_build.
(Contributed by Filipe Laíns in :gh:92897.)~threading.RLock objects. This was deprecated
in Python 3.14.
(Contributed by Bénédikt Tran in :gh:134087.):class:typing.ByteString has been removed from typing.__all__.
:class:!typing.ByteString has been deprecated since Python 3.9, and is
scheduled for removal in Python 3.17.
The undocumented keyword argument syntax for creating
:class:~typing.NamedTuple classes (for example,
Point = NamedTuple("Point", x=int, y=int)) is no longer supported.
Use the class-based syntax or the functional syntax instead.
(Contributed by Bénédikt Tran in :gh:133817.)
Using TD = TypedDict("TD") or TD = TypedDict("TD", None) to
construct a :class:~typing.TypedDict type with zero fields is no
longer supported. Use class TD(TypedDict): pass
or TD = TypedDict("TD", {}) instead.
(Contributed by Bénédikt Tran in :gh:133823.)
Added support for IEEE floating-point WAVE audio
(WAVE_FORMAT_IEEE_FLOAT) in :mod:wave.
Added :meth:wave.Wave_read.getformat, :meth:wave.Wave_write.getformat,
and :meth:wave.Wave_write.setformat for explicit frame format handling.
:meth:wave.Wave_write.setparams accepts both 7-item tuples including
format and 6-item tuples for backwards compatibility (defaulting to
WAVE_FORMAT_PCM).
WAVE_FORMAT_IEEE_FLOAT output now includes a fact chunk,
as required for non-PCM WAVE formats.
(Contributed by Lionel Koenig and Michiel W. Beijen in :gh:60729.)
getmark(), setmark() and getmarkers() methods
of the :class:~wave.Wave_read and :class:~wave.Wave_write classes,
which were deprecated since Python 3.13.
(Contributed by Bénédikt Tran in :gh:133873.)!zipimport.zipimporter.load_module.
Use :meth:zipimport.zipimporter.exec_module instead.
(Contributed by Jiahao Li in :gh:133656.):mod:base64:
+ and / characters with an alternative alphabet in
:func:~base64.b64decode and :func:~base64.urlsafe_b64decode is now
deprecated.
In future Python versions they will be errors in the strict mode and
discarded in the non-strict mode.
(Contributed by Serhiy Storchaka in :gh:125346.)CLI:
Deprecate :option:-b and :option:!-bb command-line options
and schedule them to become no-ops in Python 3.17.
These were primarily helpers for the Python 2 -> 3 transition.
Starting with Python 3.17, no :exc:BytesWarning will be raised
for these cases; use a type checker instead.
(Contributed by Nikita Sobolev in :gh:136355.)
:mod:collections.abc
The following statements now cause DeprecationWarning\ s to be emitted
at runtime:
from collections.abc import ByteStringimport collections.abc; collections.abc.ByteString.DeprecationWarning\ s were already emitted if
:class:collections.abc.ByteString was subclassed or used as the second
argument to :func:isinstance or :func:issubclass, but warnings were not
previously emitted if it was merely imported or accessed from the
:mod:!collections.abc module.
:mod:hashlib:
In hash function constructors such as :func:~hashlib.new or the
direct hash-named constructors such as :func:~hashlib.md5 and
:func:~hashlib.sha256, the optional initial data parameter could
also be passed as a keyword argument named data= or string= in
various :mod:hashlib implementations.
Support for the string keyword argument name is now deprecated and
is slated for removal in Python 3.19. Prefer passing the initial data as
a positional argument for maximum backwards compatibility.
(Contributed by Bénédikt Tran in :gh:134978.)
:mod:struct:
Calling the Struct.__new__() without required argument now is
deprecated and will be removed in Python 3.20. Calling
:meth:~object.__init__ method on initialized :class:~struct.Struct
objects is deprecated and will be removed in Python 3.20.
(Contributed by Sergey B Kirpichev and Serhiy Storchaka in :gh:143715.)
:mod:typing:
The following statements now cause DeprecationWarning\ s to be emitted
at runtime:
from typing import ByteStringimport typing; typing.ByteString.DeprecationWarning\ s were already emitted if :class:typing.ByteString
was subclassed or used as the second argument to :func:isinstance or
:func:issubclass, but warnings were not previously emitted if it was
merely imported or accessed from the :mod:!typing module.
Deprecated :func:!typing.no_type_check_decorator has been removed.
(Contributed by Nikita Sobolev in :gh:133601.)
__version__
The __version__, version and VERSION attributes have been
deprecated in these standard library modules and will be removed in
Python 3.20. Use :py:data:sys.version_info instead.
argparsecsvctypes!ctypes.macholibdecimal (use :data:decimal.SPEC_VERSION instead)http.serverimaplibipaddressjsonlogging (__date__ also deprecated)optparsepickleplatformresocketservertabnannytarfiletkinter.fonttkinter.ttkwsgiref.simple_serverxml.etree.ElementTree!xml.sax.expatreaderxml.sax.handlerzlib(Contributed by Hugo van Kemenade and Stan Ulbrych in :gh:76007.)
.. Add deprecations above alphabetically, not here at the end.
.. include:: ../deprecations/pending-removal-in-3.16.rst
.. include:: ../deprecations/pending-removal-in-3.17.rst
.. include:: ../deprecations/pending-removal-in-3.18.rst
.. include:: ../deprecations/pending-removal-in-3.19.rst
.. include:: ../deprecations/pending-removal-in-3.20.rst
.. include:: ../deprecations/pending-removal-in-future.rst
Add :c:func:PyArg_ParseArray and :c:func:PyArg_ParseArrayAndKeywords
functions to parse arguments of functions using the :c:macro:METH_FASTCALL
calling convention.
(Contributed by Victor Stinner in :gh:144175.)
Add the following functions for the new :class:frozendict type:
PyAnyDict_CheckPyAnyDict_CheckExactPyFrozenDict_CheckPyFrozenDict_CheckExactPyFrozenDict_New(Contributed by Victor Stinner in :gh:141510.)
Add :c:func:PySys_GetAttr, :c:func:PySys_GetAttrString,
:c:func:PySys_GetOptionalAttr, and :c:func:PySys_GetOptionalAttrString
functions as replacements for :c:func:PySys_GetObject.
(Contributed by Serhiy Storchaka in :gh:108512.)
Add :c:type:PyUnstable_Unicode_GET_CACHED_HASH to get the cached hash of
a string. See the documentation for caveats.
(Contributed by Petr Viktorin in :gh:131510.)
Add API for checking an extension module's ABI compatibility:
:c:data:Py_mod_abi, :c:func:PyABIInfo_Check, :c:macro:PyABIInfo_VAR
and :c:data:Py_mod_abi.
(Contributed by Petr Viktorin in :gh:137210.)
.. _whatsnew315-pybyteswriter:
Implement :pep:782, the :ref:PyBytesWriter API <pybyteswriter>.
Add functions:
PyBytesWriter_CreatePyBytesWriter_DiscardPyBytesWriter_FinishWithPointerPyBytesWriter_FinishWithSizePyBytesWriter_FinishPyBytesWriter_FormatPyBytesWriter_GetDataPyBytesWriter_GetSizePyBytesWriter_GrowAndUpdatePointerPyBytesWriter_GrowPyBytesWriter_ResizePyBytesWriter_WriteBytes(Contributed by Victor Stinner in :gh:129813.)
Add a new :c:func:PyImport_CreateModuleFromInitfunc C-API for creating
a module from a spec and initfunc.
(Contributed by Itamar Oren in :gh:116146.)
Add :c:func:PyTuple_FromArray to create a :class:tuple from an array.
(Contributed by Victor Stinner in :gh:111489.)
Add :c:func:PyObject_Dump to dump an object to stderr.
It should only be used for debugging.
(Contributed by Victor Stinner in :gh:141070.)
Add :c:func:PyUnstable_ThreadState_SetStackProtection and
:c:func:PyUnstable_ThreadState_ResetStackProtection functions to set
the stack protection base address and stack protection size of a Python
thread state.
(Contributed by Victor Stinner in :gh:139653.)
Add :c:func:PyUnstable_SetImmortal C-API function to mark objects as :term:immortal.
(Contributed by Kumar Aditya in :gh:143300.)
Restore private provisional _Py_InitializeMain() function removed in
Python 3.14.
(Contributed by Victor Stinner in :gh:142417.)
If the :c:macro:Py_TPFLAGS_MANAGED_DICT or :c:macro:Py_TPFLAGS_MANAGED_WEAKREF
flag is set then :c:macro:Py_TPFLAGS_HAVE_GC must be set too.
(Contributed by Sergey Miryanov in :gh:134786.)
:c:macro:PyDateTime_IMPORT is now thread safe. Code that directly checks PyDateTimeAPI
for NULL should be updated to call :c:macro:PyDateTime_IMPORT instead.
(Contributed by Kumar Aditya in :gh:141563.)
Private functions promoted to public C APIs:
The |pythoncapi_compat_project| can be used to get most of these new functions on Python 3.14 and older.
Remove deprecated PyUnicode functions:
!PyUnicode_AsDecodedObject:
Use :c:func:PyCodec_Decode instead.!PyUnicode_AsDecodedUnicode:
Use :c:func:PyCodec_Decode instead; Note that some codecs (for example, "base64")
may return a type other than :class:str, such as :class:bytes.!PyUnicode_AsEncodedObject:
Use :c:func:PyCodec_Encode instead.!PyUnicode_AsEncodedUnicode:
Use :c:func:PyCodec_Encode instead; Note that some codecs (for example, "base64")
may return a type other than :class:bytes, such as :class:str.(Contributed by Stan Ulbrych in :gh:133612.)
:c:func:!PyImport_ImportModuleNoBlock: deprecated alias
of :c:func:PyImport_ImportModule.
(Contributed by Bénédikt Tran in :gh:133644.)
:c:func:!PyWeakref_GetObject and :c:macro:!PyWeakref_GET_OBJECT:
use :c:func:PyWeakref_GetRef instead. The |pythoncapi_compat_project|
can be used to get :c:func:!PyWeakref_GetRef on Python 3.12 and older.
(Contributed by Bénédikt Tran in :gh:133644.)
Remove deprecated :c:func:!PySys_ResetWarnOptions.
Clear :data:sys.warnoptions and :data:!warnings.filters instead.
(Contributed by Nikita Sobolev in :gh:138886.)
The following functions are removed in favor of :c:func:PyConfig_Get.
The |pythoncapi_compat_project| can be used to get :c:func:!PyConfig_Get
on Python 3.13 and older.
Python initialization functions:
!Py_GetExecPrefix:
use :c:func:PyConfig_Get("base_exec_prefix") <PyConfig_Get>
(:data:sys.base_exec_prefix) instead.
Use :c:func:PyConfig_Get("exec_prefix") <PyConfig_Get>
(:data:sys.exec_prefix) if :ref:virtual environments <venv-def>
need to be handled.!Py_GetPath:
use :c:func:PyConfig_Get("module_search_paths") <PyConfig_Get>
(:data:sys.path) instead.!Py_GetPrefix:
use :c:func:PyConfig_Get("base_prefix") <PyConfig_Get>
(:data:sys.base_prefix) instead.
Use :c:func:PyConfig_Get("prefix") <PyConfig_Get>
(:data:sys.prefix) if :ref:virtual environments <venv-def>
need to be handled.!Py_GetProgramFullPath:
use :c:func:PyConfig_Get("executable") <PyConfig_Get>
(:data:sys.executable) instead.!Py_GetProgramName:
use :c:func:PyConfig_Get("executable") <PyConfig_Get>
(:data:sys.executable) instead.!Py_GetPythonHome:
use :c:func:PyConfig_Get("home") <PyConfig_Get> or the
:envvar:PYTHONHOME environment variable instead.(Contributed by Bénédikt Tran in :gh:133644.)
.. |pythoncapi_compat_project| replace:: |pythoncapi_compat_project_link|_ .. |pythoncapi_compat_project_link| replace:: pythoncapi-compat project .. _pythoncapi_compat_project_link: https://github.com/python/pythoncapi-compat
Deprecate :pep:456 support for providing an external definition
of the string hashing scheme. Removal is scheduled for Python 3.19.
Previously, embedders could define :c:macro:Py_HASH_ALGORITHM to be
Py_HASH_EXTERNAL to indicate that the hashing scheme was provided
externally but this feature was undocumented, untested and most likely
unused.
(Contributed by Bénédikt Tran in :gh:141226.)
For unsigned integer formats in :c:func:PyArg_ParseTuple,
accepting Python integers with value that is larger than the maximal value
for the C type or less than the minimal value for the corresponding
signed integer type of the same size is now deprecated.
(Contributed by Serhiy Storchaka in :gh:132629.)
:c:func:PyBytes_FromStringAndSize(NULL, len) <PyBytes_FromStringAndSize>
and :c:func:_PyBytes_Resize are :term:soft deprecated,
use the :c:type:PyBytesWriter API instead.
(Contributed by Victor Stinner in :gh:129813.)
:c:func:!_PyObject_CallMethodId, :c:func:!_PyObject_GetAttrId and
:c:func:!_PyUnicode_FromId are deprecated since 3.15 and will be removed in
3.20. Instead, use :c:func:PyUnicode_InternFromString() and cache the result in
the module state, then call :c:func:PyObject_CallMethod or
:c:func:PyObject_GetAttr.
(Contributed by Victor Stinner in :gh:141049.)
Deprecate :c:member:~PyComplexObject.cval field of the
:c:type:PyComplexObject type.
Use :c:func:PyComplex_AsCComplex and :c:func:PyComplex_FromCComplex
to convert a Python complex number to/from the C :c:type:Py_complex
representation.
(Contributed by Sergey B Kirpichev in :gh:128813.)
Functions :c:func:_Py_c_sum, :c:func:_Py_c_diff, :c:func:_Py_c_neg,
:c:func:_Py_c_prod, :c:func:_Py_c_quot, :c:func:_Py_c_pow and
:c:func:_Py_c_abs are :term:soft deprecated.
(Contributed by Sergey B Kirpichev in :gh:128813.)
:c:member:~PyConfig.bytes_warning is deprecated
since 3.15 and will be removed in 3.17.
(Contributed by Nikita Sobolev in :gh:136355.)
:c:macro:!Py_INFINITY macro is :term:soft deprecated,
use the C11 standard <math.h> :c:macro:!INFINITY instead.
(Contributed by Sergey B Kirpichev in :gh:141004.)
The following macros are :term:soft deprecated:
Py_ALIGNED: Prefer alignas instead.PY_FORMAT_SIZE_T: Use "z" directly.Py_LL & :c:macro:Py_ULL:
Use standard suffixes, LL & ULL.PY_LONG_LONG, :c:macro:PY_LLONG_MIN, :c:macro:PY_LLONG_MAX,
:c:macro:PY_ULLONG_MAX, :c:macro:PY_INT32_T, :c:macro:PY_UINT32_T,
:c:macro:PY_INT64_T, :c:macro:PY_UINT64_T, :c:macro:PY_SIZE_MAX:
Use C99 types/limits.Py_UNICODE_SIZE: Use sizeof(wchar_t) directly.Py_VA_COPY: Use va_copy directly.The macro :c:macro:Py_UNICODE_WIDE, which was scheduled for removal,
is :term:soft deprecated instead.
(Contributed by Petr Viktorin in :gh:146175.)
:c:macro:!Py_MATH_El and :c:macro:!Py_MATH_PIl are deprecated
since 3.15 and will be removed in 3.20.
(Contributed by Sergey B Kirpichev in :gh:141004.)
.. Add C API deprecations above alphabetically, not here at the end.
Removed implicit fallback to the bundled copy of the libmpdec library.
Now this should be explicitly enabled with :option:--with-system-libmpdec
set to no or with :option:!--without-system-libmpdec.
(Contributed by Sergey B Kirpichev in :gh:115119.)
The new configure option :option:--with-missing-stdlib-config=FILE allows
distributors to pass a JSON <https://www.json.org/json-en.html>_
configuration file containing custom error messages for :term:standard library
modules that are missing or packaged separately.
(Contributed by Stan Ulbrych and Petr Viktorin in :gh:139707.)
The new configure option :option:--with-pymalloc-hugepages enables huge
page support for :ref:pymalloc <pymalloc> arenas. When enabled, arena size
increases to 2 MiB and allocation uses MAP_HUGETLB (Linux) or
MEM_LARGE_PAGES (Windows) with automatic fallback to regular pages.
On Windows, use build.bat --pymalloc-hugepages.
At runtime, huge pages must be explicitly enabled by setting the
:envvar:PYTHON_PYMALLOC_HUGEPAGES environment variable to 1.
Annotating anonymous mmap usage is now supported if Linux kernel supports
:manpage:PR_SET_VMA_ANON_NAME <PR_SET_VMA(2const)> (Linux 5.17 or newer).
Annotations are visible in /proc/<pid>/maps if the kernel supports the feature
and :option:-X dev <-X> is passed to the Python or Python is built in :ref:debug mode <debug-build>.
(Contributed by Donghee Na in :gh:141770.)
.. _whatsnew315-windows-tail-calling-interpreter:
64-bit builds using Visual Studio 2026 (MSVC 18) may now use the new
:ref:tail-calling interpreter <whatsnew314-tail-call-interpreter>.
Results on Visual Studio 18.1.1 report between
15-20% <https://github.com/faster-cpython/ideas/blob/main/results/5800X-msvc.pgo2-vs-msvc.pgo.tc.svg>__
speedup on the geometric mean of pyperformance on Windows x86-64 over
the switch-case interpreter on an AMD Ryzen 7 5800X. We have
observed speedups ranging from 14% for large pure-Python libraries
to 40% for long-running small pure-Python scripts on Windows.
This was made possible by a new feature introduced in MSVC 18,
which the official Windows 64-bit binaries on python.org__ now use.
(Contributed by Chris Eibl, Ken Jin, and Brandt Bucher in :gh:143068.
Special thanks to Steve Dower, and the MSVC team including Hulon Jenkins.)
This section lists previously described changes and other bugfixes that may require changes to your code.
:class:sqlite3.Connection APIs have been cleaned up.
sqlite3.connect except database are now keyword-only.~sqlite3.Connection.create_function
and :meth:~sqlite3.Connection.create_aggregate are now positional-only.~sqlite3.Connection.set_authorizer,
:meth:~sqlite3.Connection.set_progress_handler and
:meth:~sqlite3.Connection.set_trace_callback is now positional-only.(Contributed by Serhiy Storchaka in :gh:133595.)
:data:resource.RLIM_INFINITY is now always positive.
Passing a negative integer value that corresponded to its old value
(such as -1 or -3, depending on platform) to
:func:resource.setrlimit and :func:resource.prlimit is now deprecated.
(Contributed by Serhiy Storchaka in :gh:137044.)
:meth:mmap.mmap.resize has been removed on platforms that don't support the
underlying syscall, instead of raising a :exc:SystemError.
A resource warning is now emitted for an unclosed
:func:xml.etree.ElementTree.iterparse iterator if it opened a file.
Use its :meth:!close method or the :func:contextlib.closing context
manager to close it.
(Contributed by Osama Abdelkader and Serhiy Storchaka in :gh:140601.)
If a short option and a single-dash long option are passed to
:meth:argparse.ArgumentParser.add_argument, dest is now inferred from
the single-dash long option. For example, in add_argument('-f', '-foo'),
dest is now 'foo' instead of 'f'.
Pass an explicit dest argument to preserve the old behavior.
(Contributed by Serhiy Storchaka in :gh:138697.)
Padding of input no longer required in :func:base64.urlsafe_b64decode.
Pass a new argument padded=True or use :func:base64.b64decode
with argument altchars=b'-_' (this works with older Python versions)
to make padding required.
(Contributed by Serhiy Storchaka in :gh:73613.)