What’s New In Python 3.12

Release

3.12.0a0

Date

July 05, 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.)

New Modules

• None yet.

Improved Modules

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 instrcutions. Use the new hasarg collection instead. (Contributed by Irit Katriel in gh-94216.)

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.)

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.)

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.)

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):

• 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 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

• 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)

• The --experimental-isolated-subinterpreters configure flag (and corresponding EXPERIMENTAL_ISOLATED_SUBINTERPRETERS) have been 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.)

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.

• 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

• 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.)

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.)

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.

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.)

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.)