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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

  • 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`.)

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

Optimizations

Deprecated

Removed

Porting to Python 3.10

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

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`.)

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`.)

Porting to Python 3.10

  • 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`.)

Removed

  • Remove the :c:func:`_Py_NewReference` and :c:func:`_Py_ForgetReference` functions from the public C API: move them to the internal C API. (Contributed by Victor Stinner in :issue:`40989`.)