What’s New In Python 3.12

Release

3.12.0a0

Date

September 24, 2022

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

New Features

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.)

New Modules

  • None yet.

Improved Modules

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.)

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.)

os

sqlite3

threading

unicodedata

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

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.)

CPython bytecode changes

Deprecated

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):

APIs:

Pending Removal in Python 3.14

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 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.)

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.)

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.)

C API Changes

New Features

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.

Deprecated

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.)

  • Leagcy Unicode APIs has 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.)