3.10.rst

What's New In Python 3.10

Release:	|release|
Date:	|today|

This article explains the new features in Python 3.10, compared to 3.9.

For full details, see the :ref:`changelog <changelog>`.

Note

Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.10 moves towards release, so it's worth checking back even after reading earlier versions.

Summary -- Release highlights

New Features

PEP 563: Postponed Evaluation of Annotations Becomes Default

In Python 3.7, postponed evaluation of annotations was added, to be enabled with a from __future__ import annotations directive. In 3.10 this became the default behavior, even without that future directive. With this being default, all annotations stored in :attr:`__annotations__` will be strings. If needed, annotations can be resolved at runtime using :func:`typing.get_type_hints`. See PEP 563 for a full description. Also, the :func:`inspect.signature` will try to resolve types from now on, and when it fails it will fall back to showing the string annotations. (Contributed by Batuhan Taskaya in :issue:`38605`.)

• The :class:`int` type has a new method :meth:`int.bit_count`, returning the number of ones in the binary expansion of a given integer, also known as the population count. (Contributed by Niklas Fiekas in :issue:`29882`.)
• The views returned by :meth:`dict.keys`, :meth:`dict.values` and :meth:`dict.items` now all have a mapping attribute that gives a :class:`types.MappingProxyType` object wrapping the original dictionary. (Contributed by Dennis Sweeney in :issue:`40890`.)
• PEP 618: The :func:`zip` function now has an optional strict flag, used to require that all the iterables have an equal length.

PEP 613: TypeAlias Annotation

PEP 484 introduced the concept of type aliases, only requiring them to be top-level unannotated assignments. This simplicity sometimes made it difficult for type checkers to distinguish between type aliases and ordinary assignments, especially when forward references or invalid types were involved. Compare:

StrCache = 'Cache[str]'  # a type alias
LOG_PREFIX = 'LOG[DEBUG]'  # a module constant

Now the :mod:`typing` module has a special annotation :data:`TypeAlias` to declare type aliases more explicitly:

StrCache: TypeAlias = 'Cache[str]'  # a type alias
LOG_PREFIX = 'LOG[DEBUG]'  # a module constant

See PEP 613 for more details.

(Contributed by Mikhail Golubev in :issue:`41923`.)

PEP604: New Type Union Operator

A new type union operator was introduced which enables the syntax X | Y. This provides a cleaner way of expressing 'either type X or type Y' instead of using :data:`typing.Union`, especially in type hints (annotations).

In previous versions of Python, to apply a type hint for functions accepting arguments of multiple types, :data:`typing.Union` was used:

def square(number: Union[int, float]) -> Union[int, float]:
    return number ** 2

Type hints can now be written in a more succinct manner:

def square(number: int | float) -> int | float:
    return number ** 2

See PEP 604 for more details.

(Contributed by Maggie Moss and Philippe Prados in :issue:`41428`.)

Other Language Changes

• Builtin and extension functions that take integer arguments no longer accept :class:`~decimal.Decimal`s, :class:`~fractions.Fraction`s and other objects that can be converted to integers only with a loss (e.g. that have the :meth:`~object.__int__` method but do not have the :meth:`~object.__index__` method). (Contributed by Serhiy Storchaka in :issue:`37999`.)

New Modules

• None yet.

Improved Modules

base64

Add :func:`base64.b32hexencode` and :func:`base64.b32hexdecode` to support the Base32 Encoding with Extended Hex Alphabet.

codecs

Add a :func:`codecs.unregister` function to unregister a codec search function. (Contributed by Hai Shi in :issue:`41842`.)

contextlib

Add a :func:`contextlib.aclosing` context manager to safely close async generators and objects representing asynchronously released resources. (Contributed by Joongi Kim and John Belmonte in :issue:`41229`.)

Add asynchronous context manager support to :func:`contextlib.nullcontext`. (Contributed by Tom Gringauz in :issue:`41543`.)

curses

The extended color functions added in ncurses 6.1 will be used transparently by :func:`curses.color_content`, :func:`curses.init_color`, :func:`curses.init_pair`, and :func:`curses.pair_content`. A new function, :func:`curses.has_extended_color_support`, indicates whether extended color support is provided by the underlying ncurses library. (Contributed by Jeffrey Kintscher and Hans Petter Jansson in :issue:`36982`.)

doctest

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

encodings

:func:`encodings.normalize_encoding` now ignores non-ASCII characters. (Contributed by Hai Shi in :issue:`39337`.)

glob

Added the root_dir and dir_fd parameters in :func:`~glob.glob` and :func:`~glob.iglob` which allow to specify the root directory for searching. (Contributed by Serhiy Storchaka in :issue:`38144`.)

inspect

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

linecache

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

os

Added :func:`os.cpu_count()` support for VxWorks RTOS. (Contributed by Peixing Xin in :issue:`41440`.)

Added a new function :func:`os.eventfd` and related helpers to wrap the eventfd2 syscall on Linux. (Contributed by Christian Heimes in :issue:`41001`.)

Added :func:`os.splice()` that allows to move data between two file descriptors without copying between kernel address space and user address space, where one of the file descriptors must refer to a pipe. (Contributed by Pablo Galindo in :issue:`41625`.)

py_compile

Added --quiet option to command-line interface of :mod:`py_compile`. (Contributed by Gregory Schevchenko in :issue:`38731`.)

shelve

The :mod:`shelve` module now uses :data:`pickle.DEFAULT_PROTOCOL` by default instead of :mod:`pickle` protocol 3 when creating shelves. (Contributed by Zackery Spytz in :issue:`34204`.)

site

When a module does not define __loader__, fall back to __spec__.loader. (Contributed by Brett Cannon in :issue:`42133`.)

sys

Add :data:`sys.orig_argv` attribute: the list of the original command line arguments passed to the Python executable. (Contributed by Victor Stinner in :issue:`23427`.)

threading

Added :func:`threading.gettrace` and :func:`threading.getprofile` to retrieve the functions set by :func:`threading.settrace` and :func:`threading.setprofile` respectively. (Contributed by Mario Corchero in :issue:`42251`.)

Add :data:`threading.__excepthook__` to allow retrieving the original value of :func:`threading.excepthook` in case it is set to a broken or a different value. (Contributed by Mario Corchero in :issue:`42308`.)

traceback

The :func:`~traceback.format_exception`, :func:`~traceback.format_exception_only`, and :func:`~traceback.print_exception` functions can now take an exception object as a positional-only argument. (Contributed by Zackery Spytz and Matthias Bussonnier in :issue:`26389`.)

types

Reintroduced the :data:`types.EllipsisType`, :data:`types.NoneType` and :data:`types.NotImplementedType` classes, providing a new set of types readily interpretable by type checkers. (Contributed by Bas van Beek in :issue:`41810`.)

unittest

Add new method :meth:`~unittest.TestCase.assertNoLogs` to complement the existing :meth:`~unittest.TestCase.assertLogs`. (Contributed by Kit Yan Choi in :issue:`39385`.)

xml

Add a :class:`~xml.sax.handler.LexicalHandler` class to the :mod:`xml.sax.handler` module. (Contributed by Jonathan Gossage and Zackery Spytz in :issue:`35018`.)

zipimport

Add methods related to PEP 451: :meth:`~zipimport.zipimporter.find_spec`, :meth:`zipimport.zipimporter.create_module`, and :meth:`zipimport.zipimporter.exec_module`. (Contributed by Brett Cannon in :issue:`42131`.

Optimizations

• Constructors :func:`str`, :func:`bytes` and :func:`bytearray` are now faster (around 30--40% for small objects). (Contributed by Serhiy Storchaka in :issue:`41334`.)
• The :mod:`runpy` module now imports fewer modules. The python3 -m module-name command startup time is 1.3x faster in average. (Contributed by Victor Stinner in :issue:`41006`.)
• The LOAD_ATTR instruction now uses new "per opcode cache" mechanism. It is about 36% faster now. (Contributed by Pablo Galindo and Yury Selivanov in :issue:`42093`, based on ideas implemented originally in PyPy and MicroPython.)
• When building Python with --enable-optimizations now -fno-semantic-interposition is added to both the compile and link line. This speeds builds of the Python interpreter created with --enable-shared with gcc by up to 30%. See this article for more details. (Contributed by Victor Stinner and Pablo Galindo in :issue:`38980`)

Deprecated

• Starting in this release, there will be a concerted effort to begin cleaning up old import semantics that were kept for Python 2.7 compatibility. Specifically, :meth:`~importlib.abc.PathEntryFinder.find_loader`/:meth:`~importlib.abc.Finder.find_module` (superseded by :meth:`~importlib.abc.Finder.find_spec`), :meth:`~importlib.abc.Loader.load_module` (superseded by :meth:`~importlib.abc.Loader.exec_module`), :meth:`~importlib.abc.Loader.module_repr` (which the import system takes care of for you), the __package__ attribute (superseded by __spec__.parent), the __loader__ attribute (superseded by __spec__.loader), and the __cached__ attribute (superseded by __spec__.cached) will slowly be removed (as well as other classes and methods in :mod:`importlib`). :exc:`ImportWarning` and/or :exc:`DeprecationWarning` will be raised as appropriate to help identify code which needs updating during this transition.
• sqlite3.OptimizedUnicode has been undocumented and obsolete since Python 3.3, when it was made an alias to :class:`str`. It is now deprecated, scheduled for removal in Python 3.12. (Contributed by Erlend E. Aasland in :issue:`42264`.)

Removed

• Removed special methods __int__, __float__, __floordiv__, __mod__, __divmod__, __rfloordiv__, __rmod__ and __rdivmod__ of the :class:`complex` class. They always raised a :exc:`TypeError`. (Contributed by Serhiy Storchaka in :issue:`41974`.)
• The ParserBase.error() method from the private and undocumented _markupbase module has been removed. :class:`html.parser.HTMLParser` is the only subclass of ParserBase and its error() implementation has already been removed in Python 3.5. (Contributed by Berker Peksag in :issue:`31844`.)
• Removed the unicodedata.ucnhash_CAPI attribute which was an internal PyCapsule object. The related private _PyUnicode_Name_CAPI structure was moved to the internal C API. (Contributed by Victor Stinner in :issue:`42157`.)
• Removed the parser module, which was deprecated in 3.9 due to the switch to the new PEG parser, as well as all the C source and header files that were only being used by the old parser, including node.h, parser.h, graminit.h and grammar.h.
• Removed the Public C API functions :c:func:`PyParser_SimpleParseStringFlags`, :c:func:`PyParser_SimpleParseStringFlagsFilename`, :c:func:`PyParser_SimpleParseFileFlags` and :c:func:`PyNode_Compile` that were deprecated in 3.9 due to the switch to the new PEG parser.

Porting to Python 3.10

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

Changes in the Python API

• The etype parameters of the :func:`~traceback.format_exception`, :func:`~traceback.format_exception_only`, and :func:`~traceback.print_exception` functions in the :mod:`traceback` module have been renamed to exc. (Contributed by Zackery Spytz and Matthias Bussonnier in :issue:`26389`.)

Build Changes

• The C99 functions :c:func:`snprintf` and :c:func:`vsnprintf` are now required to build Python. (Contributed by Victor Stinner in :issue:`36020`.)
• :mod:`sqlite3` requires SQLite 3.7.3 or higher. (Contributed by Sergey Fedoseev and Erlend E. Aasland :issue:`40744`.)

C API Changes

New Features

• The result of :c:func:`PyNumber_Index` now always has exact type :class:`int`. Previously, the result could have been an instance of a subclass of int. (Contributed by Serhiy Storchaka in :issue:`40792`.)
• Add a new :c:member:`~PyConfig.orig_argv` member to the :c:type:`PyConfig` structure: the list of the original command line arguments passed to the Python executable. (Contributed by Victor Stinner in :issue:`23427`.)
• The :c:func:`PyDateTime_DATE_GET_TZINFO` and :c:func:`PyDateTime_TIME_GET_TZINFO` macros have been added for accessing the tzinfo attributes of :class:`datetime.datetime` and :class:`datetime.time` objects. (Contributed by Zackery Spytz in :issue:`30155`.)
• Add a :c:func:`PyCodec_Unregister` function to unregister a codec search function. (Contributed by Hai Shi in :issue:`41842`.)
• The :c:func:`PyIter_Send` function was added to allow sending value into iterator without raising StopIteration exception. (Contributed by Vladimir Matveev in :issue:`41756`.)
• Added :c:func:`PyUnicode_AsUTF8AndSize` to the limited C API. (Contributed by Alex Gaynor in :issue:`41784`.)
• Added :c:func:`PyModule_AddObjectRef` function: similar to :c:func:`PyModule_AddObject` but don't steal a reference to the value on success. (Contributed by Victor Stinner in :issue:`1635741`.)
• Added :c:func:`Py_NewRef` and :c:func:`Py_XNewRef` functions to increment the reference count of an object and return the object. (Contributed by Victor Stinner in :issue:`42262`.)
• The :c:func:`PyType_FromModuleAndSpec` function now accepts NULL tp_doc slot. (Contributed by Hai Shi in :issue:`41832`.)
• The :c:func:`PyType_GetSlot` function can accept static types. (Contributed by Hai Shi and Petr Viktorin in :issue:`41073`.)

Porting to Python 3.10

• The PY_SSIZE_T_CLEAN macro must now be defined to use :c:func:`PyArg_ParseTuple` and :c:func:`Py_BuildValue` formats which use #: es#, et#, s#, u#, y#, z#, U# and Z#. See :ref:`Parsing arguments and building values <arg-parsing>` and the PEP 353. (Contributed by Victor Stinner in :issue:`40943`.)

• Since :c:func:`Py_REFCNT()` is changed to the inline static function, Py_REFCNT(obj) = new_refcnt must be replaced with Py_SET_REFCNT(obj, new_refcnt): see :c:func:`Py_SET_REFCNT()` (available since Python 3.9). For backward compatibility, this macro can be used:

  #if PY_VERSION_HEX < 0x030900A4
  #  define Py_SET_REFCNT(obj, refcnt) ((Py_REFCNT(obj) = (refcnt)), (void)0)
  #endif
  

  (Contributed by Victor Stinner in :issue:`39573`.)

• Calling :c:func:`PyDict_GetItem` without :term:`GIL` held had been allowed for historical reason. It is no longer allowed. (Contributed by Victor Stinner in :issue:`40839`.)

• PyUnicode_FromUnicode(NULL, size) and PyUnicode_FromStringAndSize(NULL, size) raise DeprecationWarning now. Use :c:func:`PyUnicode_New` to allocate Unicode object without initial data. (Contributed by Inada Naoki in :issue:`36346`.)

• The private _PyUnicode_Name_CAPI structure of the PyCapsule API unicodedata.ucnhash_CAPI has been moved to the internal C API. (Contributed by Victor Stinner in :issue:`42157`.)

• :c:func:`Py_GetPath`, :c:func:`Py_GetPrefix`, :c:func:`Py_GetExecPrefix`, :c:func:`Py_GetProgramFullPath`, :c:func:`Py_GetPythonHome` and :c:func:`Py_GetProgramName` functions now return NULL if called before :c:func:`Py_Initialize` (before Python is initialized). Use the new :ref:`Python Initialization Configuration API <init-config>` to get the :ref:`Python Path Configuration. <init-path-config>`. (Contributed by Victor Stinner in :issue:`42260`.)

Deprecated

• The PyUnicode_InternImmortal() function is now deprecated and will be removed in Python 3.12: use :c:func:`PyUnicode_InternInPlace` instead. (Contributed by Victor Stinner in :issue:`41692`.)

Removed

• PyObject_AsCharBuffer(), PyObject_AsReadBuffer(), PyObject_CheckReadBuffer(), and PyObject_AsWriteBuffer() are removed. Please migrate to new buffer protocol; :c:func:`PyObject_GetBuffer` and :c:func:`PyBuffer_Release`. (Contributed by Inada Naoki in :issue:`41103`.)

• Removed Py_UNICODE_str* functions manipulating Py_UNICODE* strings. (Contributed by Inada Naoki in :issue:`41123`.)

  • Py_UNICODE_strlen: use :c:func:`PyUnicode_GetLength` or :c:macro:`PyUnicode_GET_LENGTH`
  • Py_UNICODE_strcat: use :c:func:`PyUnicode_CopyCharacters` or :c:func:`PyUnicode_FromFormat`
  • Py_UNICODE_strcpy, Py_UNICODE_strncpy: use :c:func:`PyUnicode_CopyCharacters` or :c:func:`PyUnicode_Substring`
  • Py_UNICODE_strcmp: use :c:func:`PyUnicode_Compare`
  • Py_UNICODE_strncmp: use :c:func:`PyUnicode_Tailmatch`
  • Py_UNICODE_strchr, Py_UNICODE_strrchr: use :c:func:`PyUnicode_FindChar`

• Removed PyUnicode_GetMax(). Please migrate to new (PEP 393) APIs. (Contributed by Inada Naoki in :issue:`41103`.)

• Removed PyLong_FromUnicode(). Please migrate to :c:func:`PyLong_FromUnicodeObject`. (Contributed by Inada Naoki in :issue:`41103`.)

• Removed PyUnicode_AsUnicodeCopy(). Please use :c:func:`PyUnicode_AsUCS4Copy` or :c:func:`PyUnicode_AsWideCharString` (Contributed by Inada Naoki in :issue:`41103`.)

• Removed _Py_CheckRecursionLimit variable: it has been replaced by ceval.recursion_limit of the :c:type:`PyInterpreterState` structure. (Contributed by Victor Stinner in :issue:`41834`.)

• Removed undocumented macros Py_ALLOW_RECURSION and Py_END_ALLOW_RECURSION and the recursion_critical field of the :c:type:`PyInterpreterState` structure. (Contributed by Serhiy Storchaka in :issue:`41936`.)

• Removed the undocumented PyOS_InitInterrupts() function. Initializing Python already implicitly installs signal handlers: see :c:member:`PyConfig.install_signal_handlers`. (Contributed by Victor Stinner in :issue:`41713`.)