What's New In Python 3.12
*************************

Release:
   3.12.0a4

Date:
   February 07, 2023

This article explains the new features in Python 3.12, compared to
3.11.

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 3.12 moves
  towards release, so it's worth checking back even after reading
  earlier versions.


Summary -- Release highlights
=============================

Important deprecations, removals or restrictions:

* **PEP 623**, Remove wstr from Unicode

* **PEP 632**, Remove the "distutils" package.


Improved Error Messages
=======================

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

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

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

  >>> class A:
  ...    def __init__(self):
  ...        self.blech = 1
  ...
  ...    def foo(self):
  ...        somethin = blech

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

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

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

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

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


New Features
============

* Add Python support for the Linux perf profiler through the new
  environment variable "PYTHONPERFSUPPORT", the new command-line
  option "-X perf", as well as the new
  "sys.activate_stack_trampoline()",
  "sys.deactivate_stack_trampoline()", and
  "sys.is_stack_trampoline_active()" APIs. (Design by Pablo Galindo.
  Contributed by Pablo Galindo and Christian Heimes with contributions
  from Gregory P. Smith [Google] and Mark Shannon in gh-96123.)


Other Language Changes
======================

* "types.MappingProxyType" instances are now hashable if the
  underlying mapping is hashable. (Contributed by Serhiy Storchaka in
  gh-87995.)

* "memoryview" now supports the half-float type (the "e" format code).
  (Contributed by Dong-hee Na and Antoine Pitrou in gh-90751.)

* The parser now raises "SyntaxError" when parsing source code
  containing null bytes. (Contributed by Pablo Galindo in gh-96670.)

* "ast.parse()" now raises "SyntaxError" instead of "ValueError" when
  parsing source code containing null bytes. (Contributed by Pablo
  Galindo in gh-96670.)

* The Garbage Collector now runs only on the eval breaker mechanism of
  the Python bytecode evaluation loop instead of object allocations.
  The GC can also run when "PyErr_CheckSignals()" is called so C
  extensions that need to run for a long time without executing any
  Python code also have a chance to execute the GC periodically.
  (Contributed by Pablo Galindo in gh-97922.)

* A backslash-character pair that is not a valid escape sequence now
  generates a "SyntaxWarning", instead of "DeprecationWarning". For
  example, "re.compile("\d+\.\d+")" now emits a "SyntaxWarning"
  (""\d"" is an invalid escape sequence), use raw strings for regular
  expression: "re.compile(r"\d+\.\d+")". In a future Python version,
  "SyntaxError" will eventually be raised, instead of "SyntaxWarning".
  (Contributed by Victor Stinner in gh-98401.)

* Octal escapes with value larger than "0o377" (ex: ""\477""),
  deprecated in Python 3.11, now produce a "SyntaxWarning", instead of
  "DeprecationWarning". In a future Python version they will be
  eventually a "SyntaxError". (Contributed by Victor Stinner in
  gh-98401.)

* All builtin and extension callables expecting boolean parameters now
  accept arguments of any type instead of just "bool" and "int".
  (Contributed by Serhiy Storchaka in gh-60203.)

* Variables used in the target part of comprehensions that are not
  stored to can now be used in assignment expressions (":="). For
  example, in "[(b := 1) for a, b.prop in some_iter]", the assignment
  to "b" is now allowed. Note that assigning to variables stored to in
  the target part of comprehensions (like "a") is still disallowed, as
  per **PEP 572**. (Contributed by Nikita Sobolev in gh-100581.)


New Modules
===========

* None yet.


Improved Modules
================


array
-----

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


asyncio
-------

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

* The child watcher classes "MultiLoopChildWatcher",
  "FastChildWatcher", "AbstractChildWatcher" and "SafeChildWatcher"
  are deprecated and will be removed in Python 3.14. It is recommended
  to not manually configure a child watcher as the event loop now uses
  the best available child watcher for each platform
  ("PidfdChildWatcher" if supported and "ThreadedChildWatcher"
  otherwise). (Contributed by Kumar Aditya in gh-94597.)

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

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

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


inspect
-------

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


pathlib
-------

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

* Add *walk_up* optional parameter to "pathlib.PurePath.relative_to()"
  to allow the insertion of ".." entries in the result; this behavior
  is more consistent with "os.path.relpath()". (Contributed by
  Domenico Ragusa in bpo-40358.)

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


dis
---

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


fractions
---------

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


math
----

* Added "math.sumprod()" for computing a sum of products. (Contributed
  by Raymond Hettinger in gh-100485.)


os
--

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

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


os.path
-------

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

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


shutil
------

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


sqlite3
-------

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

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


threading
---------

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


unicodedata
-----------

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


uuid
----

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


tempfile
--------

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


sys
---

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


Optimizations
=============

* Removed "wstr" and "wstr_length" members from Unicode objects. It
  reduces object size by 8 or 16 bytes on 64bit platform. (**PEP
  623**) (Contributed by Inada Naoki in gh-92536.)

* Added experimental support for using the BOLT binary optimizer in
  the build process, which improves performance by 1-5%. (Contributed
  by Kevin Modzelewski in gh-90536.)

* Speed up the regular expression substitution (functions "re.sub()"
  and "re.subn()" and corresponding "re.Pattern" methods) for
  replacement strings containing group references by 2--3 times.
  (Contributed by Serhiy Storchaka in gh-91524.)


CPython bytecode changes
========================

* Removed the "LOAD_METHOD" instruction. It has been merged into
  "LOAD_ATTR". "LOAD_ATTR" will now behave like the old "LOAD_METHOD"
  instruction if the low bit of its oparg is set. (Contributed by Ken
  Jin in gh-93429.)


Demos and Tools
===============

* Remove the "Tools/demo/" directory which contained old demo scripts.
  A copy can be found in the old-demos project. (Contributed by Victor
  Stinner in gh-97681.)

* Remove outdated example scripts of the "Tools/scripts/" directory. A
  copy can be found in the old-demos project. (Contributed by Victor
  Stinner in gh-97669.)


Deprecated
==========

* "typing.Hashable" and "typing.Sized" aliases for
  "collections.abc.Hashable" and "collections.abc.Sized". (gh-94309.)

* The "sqlite3" default adapters and converters are now deprecated.
  Instead, use the Adapter and converter recipes and tailor them to
  your needs. (Contributed by Erlend E. Aasland in gh-90016.)

* The 3-arg signatures (type, value, traceback) of "throw()",
  "throw()" and "athrow()" are deprecated and may be removed in a
  future version of Python. Use the single-arg versions of these
  functions instead. (Contributed by Ofey Chan in gh-89874.)

* "DeprecationWarning" is now raised when "__package__" on a module
  differs from "__spec__.parent" (previously it was "ImportWarning").
  (Contributed by Brett Cannon in gh-65961.)

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

* The "xml.etree.ElementTree" module now emits "DeprecationWarning"
  when testing the truth value of an "xml.etree.ElementTree.Element".
  Before, the Python implementation emitted "FutureWarning", and the C
  implementation emitted nothing.

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


Pending Removal in Python 3.13
------------------------------

The following modules and APIs have been deprecated in earlier Python
releases, and will be removed in Python 3.13.

Modules (see **PEP 594**):

* "aifc"

* "audioop"

* "cgi"

* "cgitb"

* "chunk"

* "crypt"

* "imghdr"

* "mailcap"

* "msilib"

* "nis"

* "nntplib"

* "ossaudiodev"

* "pipes"

* "sndhdr"

* "spwd"

* "sunau"

* "telnetlib"

* "uu"

* "xdrlib"

APIs:

* "configparser.LegacyInterpolation" (gh-90765)

* "locale.getdefaultlocale()" (gh-90817)

* "turtle.RawTurtle.settiltangle()" (gh-50096)

* "unittest.findTestCases()" (gh-50096)

* "unittest.makeSuite()" (gh-50096)

* "unittest.getTestCaseNames()" (gh-50096)

* "webbrowser.MacOSX" (gh-86421)


Pending Removal in Python 3.14
==============================

* Deprecated the following "importlib.abc" classes, scheduled for
  removal in Python 3.14:

  * "importlib.abc.ResourceReader"

  * "importlib.abc.Traversable"

  * "importlib.abc.TraversableResources"

  Use "importlib.resources.abc" classes instead:

  * "importlib.resources.abc.Traversable"

  * "importlib.resources.abc.TraversableResources"

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

* Creating "immutable types" with mutable bases using the C API.

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

* Testing the truth value of an "xml.etree.ElementTree.Element" is
  deprecated and will raise an exception in Python 3.14.

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


Pending Removal in Future Versions
----------------------------------

The following APIs were deprecated in earlier Python versions and will
be removed, although there is currently no date scheduled for their
removal.

* "typing.Text" (gh-92332)

* 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)


Removed
=======

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

* Removed many old deprecated "unittest" features:

  * A number of "TestCase" method aliases:

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

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

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

  * Undocumented "TestLoader.loadTestsFromModule" parameter
    *use_load_tests* (deprecated and ignored since Python 3.2).

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

  (Contributed by Serhiy Storchaka in bpo-45162.)

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

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

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

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

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

  * "sqlite3.enable_shared_cache()"

  * "sqlite3.OptimizedUnicode"

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

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

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

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

* "asynchat" and "asyncore" have been removed according to the
  schedule in **PEP 594**, having been deprecated in Python 3.6. Use
  "asyncio" instead. (Contributed by Nikita Sobolev in gh-96580.)

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

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

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

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

* Remove the "locale.format()" function, deprecated in Python 3.7: use
  "locale.format_string()" instead. (Contributed by Victor Stinner in
  gh-94226.)

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

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

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

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

* Many previously deprecated cleanups in "importlib" have now been
  completed:

  * References to, and support for "module_repr()" has been
    eradicated.

* "importlib.util.set_package" has been removed. (Contributed by Brett
  Cannon in gh-65961.)

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

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

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


Porting to Python 3.12
======================

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


Changes in the Python API
-------------------------

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

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

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

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

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

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

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


Build Changes
=============

* Python no longer uses "setup.py" to build shared C extension
  modules. Build parameters like headers and libraries are detected in
  "configure" script. Extensions are built by "Makefile". Most
  extensions use "pkg-config" and fall back to manual detection.
  (Contributed by Christian Heimes in gh-93939.)

* "va_start()" with two parameters, like "va_start(args, format)," is
  now required to build Python. "va_start()" is no longer called with
  a single parameter. (Contributed by Kumar Aditya in gh-93207.)

* CPython now uses the ThinLTO option as the default link time
  optimization policy if the Clang compiler accepts the flag.
  (Contributed by Dong-hee Na in gh-89536.)

* Add "COMPILEALL_OPTS" variable in Makefile to override "compileall"
  options (default: "-j0") in "make install". Also merged the 3
  "compileall" commands into a single command to build .pyc files for
  all optimization levels (0, 1, 2) at once. (Contributed by Victor
  Stinner in gh-99289.)


C API Changes
=============


New Features
------------

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

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

  * "Py_TPFLAGS_HAVE_VECTORCALL"

  * "PyVectorcall_NARGS()"

  * "PyVectorcall_Call()"

  * "vectorcallfunc"

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

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

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

  * "PyObject_Vectorcall()"

  * "PyObject_VectorcallMethod()"

  * "PY_VECTORCALL_ARGUMENTS_OFFSET"

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

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

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

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

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

* Added "PyCode_AddWatcher()" and "PyCode_ClearWatcher()" APIs to
  register callbacks to receive notification on creation and
  destruction of code objects. (Contributed by Itamar Ostricher in
  gh-91054.)

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


Porting to Python 3.12
----------------------

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

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

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

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

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

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

* Fixed wrong sign placement in "PyUnicode_FromFormat()" and
  "PyUnicode_FromFormatV()". (Contributed by Philip Georgi in
  gh-95504.)

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

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

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


Deprecated
----------

* Deprecate global configuration variable:

  * "Py_DebugFlag": use "PyConfig.parser_debug"

  * "Py_VerboseFlag": use "PyConfig.verbose"

  * "Py_QuietFlag": use "PyConfig.quiet"

  * "Py_InteractiveFlag": use "PyConfig.interactive"

  * "Py_InspectFlag": use "PyConfig.inspect"

  * "Py_OptimizeFlag": use "PyConfig.optimization_level"

  * "Py_NoSiteFlag": use "PyConfig.site_import"

  * "Py_BytesWarningFlag": use "PyConfig.bytes_warning"

  * "Py_FrozenFlag": use "PyConfig.pathconfig_warnings"

  * "Py_IgnoreEnvironmentFlag": use "PyConfig.use_environment"

  * "Py_DontWriteBytecodeFlag": use "PyConfig.write_bytecode"

  * "Py_NoUserSiteDirectory": use "PyConfig.user_site_directory"

  * "Py_UnbufferedStdioFlag": use "PyConfig.buffered_stdio"

  * "Py_HashRandomizationFlag": use "PyConfig.use_hash_seed" and
    "PyConfig.hash_seed"

  * "Py_IsolatedFlag": use "PyConfig.isolated"

  * "Py_LegacyWindowsFSEncodingFlag": use
    "PyConfig.legacy_windows_fs_encoding"

  * "Py_LegacyWindowsStdioFlag": use "PyConfig.legacy_windows_stdio"

  * "Py_FileSystemDefaultEncoding": use "PyConfig.filesystem_encoding"

  * "Py_FileSystemDefaultEncodeErrors": use
    "PyConfig.filesystem_errors"

  * "Py_UTF8Mode": use "PyPreConfig.utf8_mode" (see
    "Py_PreInitialize()")

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

* Creating "immutable types" with mutable bases is deprecated and will
  be disabled in Python 3.14.

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

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

  * "PyMemberDef", "PyMember_GetOne()" and "PyMember_SetOne()"

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

  * The flags "Py_READONLY" (previously "READONLY") and
    "Py_AUDIT_READ" (previously all uppercase)

  Several items are not exposed from "Python.h":

  * "T_OBJECT" (use "Py_T_OBJECT_EX")

  * "T_NONE" (previously undocumented, and pretty quirky)

  * The macro "WRITE_RESTRICTED" which does nothing.

  * The macros "RESTRICTED" and "READ_RESTRICTED", equivalents of
    "Py_AUDIT_READ".

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

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

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


Removed
-------

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

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

     * "PyUnicode_WCHAR_KIND"

     * "PyUnicode_AS_UNICODE()"

     * "PyUnicode_AsUnicode()"

     * "PyUnicode_AsUnicodeAndSize()"

     * "PyUnicode_AS_DATA()"

     * "PyUnicode_FromUnicode()"

     * "PyUnicode_GET_SIZE()"

     * "PyUnicode_GetSize()"

     * "PyUnicode_GET_DATA_SIZE()"

* Remove the "PyUnicode_InternImmortal()" function and the
  "SSTATE_INTERNED_IMMORTAL" macro. (Contributed by Victor Stinner in
  gh-85858.)

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

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