What’s new in Python 3.15

Editor:

Hugo van Kemenade

This article explains the new features in Python 3.15, compared to 3.14.

For full details, see the 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.

Summary – Release highlights

New features

PEP 799: High frequency statistical sampling profiler

A new statistical sampling profiler has been added to the new profiling module as profiling.sampling. This profiler enables low-overhead performance analysis of running Python processes without requiring code modification or process restart.

Unlike deterministic profilers (cProfile and profile) 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.

Key features include:

  • Zero-overhead profiling: Attach to any running Python process without affecting its performance

  • No code modification required: Profile existing applications without restart

  • Real-time statistics: Monitor sampling quality during data collection

  • Multiple output formats: Generate both detailed statistics and flamegraph data

  • Thread-aware profiling: Option to profile all threads or just the main thread

Profile process 1234 for 10 seconds with default settings:

python -m profiling.sampling 1234

Profile with custom interval and duration, save to file:

python -m profiling.sampling -i 50 -d 30 -o profile.stats 1234

Generate collapsed stacks for flamegraph:

python -m profiling.sampling --collapsed 1234

Profile all threads and sort by total time:

python -m profiling.sampling -a --sort-tottime 1234

The profiler generates statistical estimates of where time is spent:

Real-time sampling stats: Mean: 100261.5Hz (9.97µs) Min: 86333.4Hz (11.58µs) Max: 118807.2Hz (8.42µs) Samples: 400001
Captured 498841 samples in 5.00 seconds
Sample rate: 99768.04 samples/sec
Error rate: 0.72%
Profile Stats:
      nsamples   sample%   tottime (s)    cumul%   cumtime (s)  filename:lineno(function)
      43/418858       0.0         0.000      87.9         4.189  case.py:667(TestCase.run)
    3293/418812       0.7         0.033      87.9         4.188  case.py:613(TestCase._callTestMethod)
  158562/158562      33.3         1.586      33.3         1.586  test_compile.py:725(TestSpecifics.test_compiler_recursion_limit.<locals>.check_limit)
  129553/129553      27.2         1.296      27.2         1.296  ast.py:46(parse)
      0/128129       0.0         0.000      26.9         1.281  test_ast.py:884(AST_Tests.test_ast_recursion_limit.<locals>.check_limit)
        7/67446       0.0         0.000      14.2         0.674  test_compile.py:729(TestSpecifics.test_compiler_recursion_limit)
        6/60380       0.0         0.000      12.7         0.604  test_ast.py:888(AST_Tests.test_ast_recursion_limit)
        3/50020       0.0         0.000      10.5         0.500  test_compile.py:727(TestSpecifics.test_compiler_recursion_limit)
        1/38011       0.0         0.000       8.0         0.380  test_ast.py:886(AST_Tests.test_ast_recursion_limit)
        1/25076       0.0         0.000       5.3         0.251  test_compile.py:728(TestSpecifics.test_compiler_recursion_limit)
    22361/22362       4.7         0.224       4.7         0.224  test_compile.py:1368(TestSpecifics.test_big_dict_literal)
        4/18008       0.0         0.000       3.8         0.180  test_ast.py:889(AST_Tests.test_ast_recursion_limit)
      11/17696       0.0         0.000       3.7         0.177  subprocess.py:1038(Popen.__init__)
    16968/16968       3.6         0.170       3.6         0.170  subprocess.py:1900(Popen._execute_child)
        2/16941       0.0         0.000       3.6         0.169  test_compile.py:730(TestSpecifics.test_compiler_recursion_limit)

Legend:
  nsamples: Direct/Cumulative samples (direct executing / on call stack)
  sample%: Percentage of total samples this function was directly executing
  tottime: Estimated total time spent directly in this function
  cumul%: Percentage of total samples when this function was on the call stack
  cumtime: Estimated cumulative time (including time in called functions)
  filename:lineno(function): Function location and name

Summary of Interesting Functions:

Functions with Highest Direct/Cumulative Ratio (Hot Spots):
  1.000 direct/cumulative ratio, 33.3% direct samples: test_compile.py:(TestSpecifics.test_compiler_recursion_limit.<locals>.check_limit)
  1.000 direct/cumulative ratio, 27.2% direct samples: ast.py:(parse)
  1.000 direct/cumulative ratio, 3.6% direct samples: subprocess.py:(Popen._execute_child)

Functions with Highest Call Frequency (Indirect Calls):
  418815 indirect calls, 87.9% total stack presence: case.py:(TestCase.run)
  415519 indirect calls, 87.9% total stack presence: case.py:(TestCase._callTestMethod)
  159470 indirect calls, 33.5% total stack presence: test_compile.py:(TestSpecifics.test_compiler_recursion_limit)

Functions with Highest Call Magnification (Cumulative/Direct):
  12267.9x call magnification, 159470 indirect calls from 13 direct: test_compile.py:(TestSpecifics.test_compiler_recursion_limit)
  10581.7x call magnification, 116388 indirect calls from 11 direct: test_ast.py:(AST_Tests.test_ast_recursion_limit)
  9740.9x call magnification, 418815 indirect calls from 43 direct: case.py:(TestCase.run)

The profiler automatically identifies performance bottlenecks through statistical analysis, highlighting functions with high CPU usage and call frequency patterns.

This capability is particularly valuable for debugging performance issues in production systems where traditional profiling approaches would be too intrusive.

See also

PEP 799 for further details.

(Contributed by Pablo Galindo and László Kiss Kollár in gh-135953.)

Improved error messages

  • The interpreter now provides more helpful suggestions in 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:

    @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:

    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'?

Other language changes

  • 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 opt-in 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 PYTHONUTF8=0 environment variable or the -X utf8=0 command-line option.

    See also

    PEP 686 for further details.

    (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 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:

    >>> class A:
...     pass
>>> a = A()
>>> a.abcde = 1
>>> del a.abcdf
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 environment variables. (Contributed by Peter Bierma in gh-134170.)

  • The __repr__() of ImportError and 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 __dict__ and __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 -W option and the 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 Decimal and Fraction), not only integers or floats, although this does not improve precision. (Contributed by Serhiy Storchaka in gh-67795.)

New modules

  • None yet.

Improved modules

calendar

  • Calendar pages generated by the 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.)

collections

  • Added collections.Counter.__xor__() and collections.Counter.__ixor__() to compute the symmetric difference between Counter objects. (Contributed by Raymond Hettinger in gh-138682.)

collections.abc

  • collections.abc.ByteString has been removed from collections.abc.__all__. collections.abc.ByteString has been deprecated since Python 3.12, and is scheduled for removal in Python 3.17.

  • The following statements now cause DeprecationWarnings to be emitted at runtime:

    • from collections.abc import ByteString

    • import collections.abc; collections.abc.ByteString.

    DeprecationWarnings were already emitted if collections.abc.ByteString was subclassed or used as the second argument to isinstance() or issubclass(), but warnings were not previously emitted if it was merely imported or accessed from the collections.abc module.

dbm

  • Added new reorganize() methods to dbm.dumb and dbm.sqlite3 which allow to recover unused free space previously occupied by deleted entries. (Contributed by Andrea Oliveri in gh-134004.)

difflib

hashlib

  • Ensure that hash functions guaranteed to be always available exist as attributes of hashlib even if they will not work at runtime due to missing backend implementations. For instance, hashlib.md5 will no longer raise AttributeError if OpenSSL is not available and Python has been built without MD5 support. (Contributed by Bénédikt Tran in gh-136929.)

http.client

  • A new max_response_headers keyword-only parameter has been added to HTTPConnection and HTTPSConnection constructors. This parameter overrides the default maximum number of allowed response headers. (Contributed by Alexander Enrique Urieles Nieto in gh-131724.)

http.cookies

  • Allow ‘"’ double quotes in cookie values. (Contributed by Nick Burns and Senthil Kumaran in gh-92936.)

locale

  • setlocale() now supports language codes with @-modifiers. @-modifiers are no longer silently removed in getlocale(), but included in the language code. (Contributed by Serhiy Storchaka in gh-137729.)

math

mmap

  • 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.)

os

  • Add os.statx() on Linux kernel versions 4.11 and later with glibc versions 2.28 and later. (Contributed by Jeffrey Bosboom in gh-83714.)

os.path

resource

shelve

  • Added new reorganize() method to shelve used to recover unused free space previously occupied by deleted entries. (Contributed by Andrea Oliveri in gh-134004.)

socket

  • Add constants for the ISO-TP CAN protocol. (Contributed by Patrick Menschel and Stefan Tatschner in gh-86819.)

sqlite3

  • The command-line interface 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 Controlling color for details. (Contributed by Stan Ulbrych and Łukasz Langa in gh-133461.)

ssl

  • Indicate through ssl.HAS_PSK_TLS13 whether the 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 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 ssl.SSLContext.set_ciphersuites() for setting TLS 1.3 ciphers. For TLS 1.2 or earlier, 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:

    (Contributed by Ron Frederick in gh-138252.)

sys

  • Add sys.abi_info namespace to improve access to ABI information. (Contributed by Klaus Zimmermann in gh-137476.)

tarfile

timeit

  • The command-line interface now colorizes error tracebacks by default. This can be controlled with environment variables. (Contributed by Yi Hong in gh-139374.)

types

unittest

xml.parsers.expat

zlib

Optimizations

module_name

  • TODO

Removed

ctypes

  • Removed the undocumented function ctypes.SetPointerType(), which has been deprecated since Python 3.13. (Contributed by Bénédikt Tran in gh-133866.)

glob

  • Removed the undocumented glob.glob0() and glob.glob1() functions, which have been deprecated since Python 3.13. Use glob.glob() and pass a directory to its root_dir argument instead. (Contributed by Barney Gale in gh-137466.)

http.server

  • Removed the CGIHTTPRequestHandler class and the --cgi flag from the python -m http.server command-line interface. They were deprecated in Python 3.13. (Contributed by Bénédikt Tran in gh-133810.)

importlib.resources

mimetypes

  • Add application/toml. (Contributed by Gil Forcada in gh-139959.)

  • Rename application/x-texinfo to application/texinfo. (Contributed by Charlie Lin in gh-140165)

pathlib

  • Removed deprecated pathlib.PurePath.is_reserved(). Use os.path.isreserved() to detect reserved paths on Windows. (Contributed by Nikita Sobolev in gh-133875.)

platform

  • Removed the platform.java_ver() function, which was deprecated since Python 3.13. (Contributed by Alexey Makridenko in gh-133604.)

sre_*

  • Removed sre_compile, sre_constants and sre_parse modules. (Contributed by Stan Ulbrych in gh-135994.)

sysconfig

threading

  • Remove support for arbitrary positional or keyword arguments in the C implementation of RLock objects. This was deprecated in Python 3.14. (Contributed by Bénédikt Tran in gh-134087.)

typing

  • The undocumented keyword argument syntax for creating 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 TypedDict type with zero field is no longer supported. Use class TD(TypedDict): pass or TD = TypedDict("TD", {}) instead. (Contributed by Bénédikt Tran in gh-133823.)

  • Code like class ExtraTypeVars(P1[S], Protocol[T, T2]): ... now raises a 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.)

  • typing.ByteString has been removed from typing.__all__. typing.ByteString has been deprecated since Python 3.9, and is scheduled for removal in Python 3.17.

  • The following statements now cause DeprecationWarnings to be emitted at runtime:

    • from typing import ByteString

    • import typing; typing.ByteString.

    DeprecationWarnings were already emitted if typing.ByteString was subclassed or used as the second argument to isinstance() or issubclass(), but warnings were not previously emitted if it was merely imported or accessed from the typing module.

  • Deprecated typing.no_type_check_decorator() has been removed. (Contributed by Nikita Sobolev in gh-133601.)

unicodedata

  • The Unicode database has been updated to Unicode 17.0.0.

wave

  • Removed the getmark(), setmark() and getmarkers() methods of the Wave_read and Wave_write classes, which were deprecated since Python 3.13. (Contributed by Bénédikt Tran in gh-133873.)

zipimport

Deprecated

New deprecations

  • CLI:

    • Deprecate -b and -bb command-line options and schedule them to become no-op in Python 3.17. These were primarily helpers for the Python 2 -> 3 transition. Starting with Python 3.17, no BytesWarning will be raised for these cases; use a type checker instead.

      (Contributed by Nikita Sobolev in gh-136355.)

  • hashlib:

    • In hash function constructors such as new() or the direct hash-named constructors such as md5() and sha256(), their optional initial data parameter could also be passed a keyword argument named data= or string= in various 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.)

  • __version__

Pending removal in Python 3.16

Pending removal in Python 3.17

  • collections.abc:

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

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

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

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

  • typing:

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

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

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

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

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

Pending removal in Python 3.19

  • ctypes:

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

  • hashlib:

    • In hash function constructors such as new() or the direct hash-named constructors such as md5() and sha256(), their optional initial data parameter could also be passed a keyword argument named data= or string= in various hashlib implementations.

      Support for the string keyword argument name is now deprecated and slated for removal in Python 3.19.

      Before Python 3.13, the string keyword parameter was not correctly supported depending on the backend implementation of hash functions. Prefer passing the initial data as a positional argument for maximum backwards compatibility.

Pending removal in Python 3.20

Pending removal in future versions

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

  • argparse:

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

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

    • The argparse.FileType type converter is deprecated.

  • builtins:

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

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

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

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

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

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

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

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

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

  • codeobject.co_lnotab: use the codeobject.co_lines() method instead.

  • datetime:

    • utcnow(): use datetime.datetime.now(tz=datetime.UTC).

    • utcfromtimestamp(): use datetime.datetime.fromtimestamp(timestamp, tz=datetime.UTC).

  • gettext: Plural value must be an integer.

  • importlib:

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

  • importlib.metadata:

    • EntryPoints tuple interface.

    • Implicit None on return values.

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

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

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

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

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

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

  • ssl options and protocols:

    • ssl.SSLContext without protocol argument is deprecated.

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

    • ssl.OP_NO_SSL* options

    • ssl.OP_NO_TLS* options

    • ssl.PROTOCOL_SSLv3

    • ssl.PROTOCOL_TLS

    • ssl.PROTOCOL_TLSv1

    • ssl.PROTOCOL_TLSv1_1

    • ssl.PROTOCOL_TLSv1_2

    • ssl.TLSVersion.SSLv3

    • ssl.TLSVersion.TLSv1

    • ssl.TLSVersion.TLSv1_1

  • threading methods:

  • typing.Text (gh-92332).

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

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

  • urllib.parse deprecated functions: urlparse() instead

    • splitattr()

    • splithost()

    • splitnport()

    • splitpasswd()

    • splitport()

    • splitquery()

    • splittag()

    • splittype()

    • splituser()

    • splitvalue()

    • to_bytes()

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

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

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

C API changes

New features

Porting to Python 3.15

Removed C APIs

  • Remove deprecated PyUnicode functions:

    • PyUnicode_AsDecodedObject(): Use PyCodec_Decode() instead.

    • PyUnicode_AsDecodedUnicode(): Use PyCodec_Decode() instead; Note that some codecs (for example, “base64”) may return a type other than str, such as bytes.

    • PyUnicode_AsEncodedObject(): Use PyCodec_Encode() instead.

    • PyUnicode_AsEncodedUnicode(): Use PyCodec_Encode() instead; Note that some codecs (for example, “base64”) may return a type other than bytes, such as str.

    (Contributed by Stan Ulbrych in gh-133612.)

  • PyImport_ImportModuleNoBlock(): deprecated alias of PyImport_ImportModule(). (Contributed by Bénédikt Tran in gh-133644.)

  • PyWeakref_GetObject() and PyWeakref_GET_OBJECT: use PyWeakref_GetRef() instead. The pythoncapi-compat project can be used to get PyWeakref_GetRef() on Python 3.12 and older. (Contributed by Bénédikt Tran in gh-133644.)

  • Remove deprecated PySys_ResetWarnOptions(). Clear sys.warnoptions and warnings.filters instead.

    (Contributed by Nikita Sobolev in gh-138886.)

The following functions are removed in favor of PyConfig_Get(). The pythoncapi-compat project can be used to get PyConfig_Get() on Python 3.13 and older.

Deprecated C APIs

Build changes

  • Removed implicit fallback to the bundled copy of the libmpdec library. Now this should be explicitly enabled with --with-system-libmpdec set to no or with --without-system-libmpdec. (Contributed by Sergey B Kirpichev in gh-115119.)

Porting to Python 3.15

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