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

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

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 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`.)

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

Now, type hints can 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`.)

• 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`.)

• None yet.

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

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

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`.)

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

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`.)

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

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

The :mod:`shelve` module now uses :mod:`pickle` default protocol for the Python version in use rather than protocol version 3. (Contributed by Marco Castelluccio in :issue:`34204`.)

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`.)

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`.)

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

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`.)

• 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`.)
• 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`)

• 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.

• 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`.)

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

• 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`.)

• 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`.)

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

  #if PY_VERSION_HEX < 0x030900A4
  #  define Py_SET_TYPE(obj, type) ((Py_TYPE(obj) = (type)), (void)0)
  #endif
  

  (Contributed by Dong-hee Na in :issue:`39573`.)

• 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`.)

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

  #if PY_VERSION_HEX < 0x030900A4
  #  define Py_SET_SIZE(obj, size) ((Py_SIZE(obj) = (size)), (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`.)

• 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`.)

• 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`.)