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

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

• 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.

• 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.

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`.)

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`.)

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 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`.)

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 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`.)

• 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`.)