What’s New In Python 3.12¶
September 24, 2022
This article explains the new features in Python 3.12, compared to 3.11.
For full details, see the changelog.
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
Other Language Changes¶
Pseudo instruction opcodes (which are used by the compiler but do not appear in executable bytecode) are now exposed in the
HAVE_ARGUMENTis still relevant to real opcodes, but it is not useful for pseudo instructions. Use the new
hasargcollection instead. (Contributed by Irit Katriel in gh-94216.)
The Unicode database has been updated to version 15.0.0. (Contributed by Benjamin Peterson in gh-96734).
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¶
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):
Pending Removal in Python 3.14¶
Deprecated the following
importlib.abcclasses, scheduled for removal in Python 3.14:
(Contributed by Jason R. Coombs and Hugo van Kemenade in gh-93963.)
immutable typeswith mutable bases using the C API.
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.
Currently Python accepts numeric literals immediately followed by keywords, for example
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
or. In a future release it will be changed to a syntax error. (gh-87999)
Removed many old deprecated
A number of
You can use https://github.com/isidentical/teyit to automatically modernise your unit tests.
Undocumented and broken
assertDictContainsSubset(deprecated in Python 3.2).
TestLoader.loadTestsFromModuleparameter use_load_tests (deprecated and ignored since Python 3.2).
An alias of the
_TextTestResult(deprecated in Python 3.2).
(Contributed by Serhiy Storchaka in bpo-45162.)
The following undocumented
sqlite3features, deprecated in Python 3.10, are now removed:
If a shared cache must be used, open the database in URI mode using the
sqlite3.OptimizedUnicodetext factory has been an alias for
strsince Python 3.3. Code that previously set the text factory to
OptimizedUnicodecan either use
strexplicitly, or rely on the default value which is also
(Contributed by Erlend E. Aasland in gh-92548.)
--experimental-isolated-subinterpretersconfigure flag (and corresponding
EXPERIMENTAL_ISOLATED_SUBINTERPRETERS) have been removed.
smtpdhas 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.)
_pyio.OpenWrapper, deprecated in Python 3.10: just use
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.)
gzip: Remove the
gzip.GzipFile, deprecated since Python 2.6, use the
nameattribute instead. In write mode, the
'.gz'file extension if it was not present. (Contributed by Victor Stinner in gh-94196.)
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.)
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
copy()method, only a
__copy__()method. (Contributed by Victor Stinner in gh-94383.)
ssl.wrap_socket()function, deprecated in Python 3.7: instead, create a
ssl.SSLContextobject and call its
ssl.SSLContext.wrap_socketmethod. 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.ArgumentParserchanged encoding and error handler for reading arguments from file (e.g.
fromfile_prefix_charsoption) 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.
Python no longer uses
setup.pyto build shared C extension modules. Build parameters like headers and libraries are detected in
configurescript. Extensions are built by
Makefile. Most extensions use
pkg-configand 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¶
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.)
Py_TPFLAGS_HAVE_VECTORCALLflag 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
immutableflag). Mutable types that do not override
tp_callnow inherit the
Py_TPFLAGS_HAVE_VECTORCALLflag. (Contributed by Petr Viktorin in gh-93274.)
Py_TPFLAGS_MANAGED_WEAKREFflags have been added. This allows extensions classes to support object
__dict__and weakrefs with less bookkeeping, using less memory and with faster access.
Added two new public functions,
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.)
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
Argument parsing functions like
Py_UNICODE*based format (e.g.
Z) anymore. Please migrate to other formats for Unicode like
tp_weaklistfor all static builtin types is always
NULL. This is an internal-only field on
PyTypeObjectbut 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)
PyTypeObject.tp_subclassesmay 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.
An unrecognized format character in
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.)
Extension classes wanting to add a
__dict__or weak reference slot should use
tp_weaklistoffset, respectively. The use of
tp_weaklistoffsetis still supported, but does not fully support multiple inheritance (:gh: 95589), and performance may be worse. Classes declaring
_PyObject_ClearManagedDict()to traverse and clear their instance’s dictionaries. To clear weakrefs, call
PyObject_ClearWeakRefs(), as before.
Deprecate global configuration variable:
immutable typeswith mutable bases is deprecated and will be disabled in Python 3.14.
token.hheader file. There was never any public tokenizer C API. The
token.hheader 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_InternImmortal()function and the
SSTATE_INTERNED_IMMORTALmacro. (Contributed by Victor Stinner in gh-85858.)