What’s New In Python 3.10

Release

3.10.0a0

Date

August 03, 2020

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

For full details, see the 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 int type has a new method 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 bpo-29882.)

  • The views returned by dict.keys(), dict.values() and dict.items() now all have a mapping attribute that gives a types.MappingProxyType object wrapping the original dictionary. (Contributed by Dennis Sweeney in bpo-40890.)

  • PEP 618: The zip() function now has an optional strict flag, used to require that all the iterables have an equal length.

Other Language Changes

  • Builtin and extension functions that take integer arguments no longer accept Decimals, Fractions and other objects that can be converted to integers only with a loss (e.g. that have the __int__() method but do not have the __index__() method). (Contributed by Serhiy Storchaka in bpo-37999.)

New Modules

  • None yet.

Improved Modules

glob

Added the root_dir and dir_fd parameters in glob() and iglob() which allow to specify the root directory for searching. (Contributed by Serhiy Storchaka in bpo-38144.)

py_compile

Added --quiet option to command-line interface of py_compile. (Contributed by Gregory Schevchenko in bpo-38731.)

sys

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

Optimizations

  • Constructors str(), bytes() and bytearray() are now faster (around 30–40% for small objects). (Contributed by Serhiy Storchaka in bpo-41334.)

  • The 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 bpo-41006.)

Deprecated

Removed

  • The ParserBase.error() method from the private and undocumented _markupbase module has been removed. 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 bpo-31844.)

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 snprintf() and vsnprintf() are now required to build Python. (Contributed by Victor Stinner in bpo-36020.)

C API Changes

New Features

  • The result of PyNumber_Index() now always has exact type int. Previously, the result could have been an instance of a subclass of int. (Contributed by Serhiy Storchaka in bpo-40792.)

  • Add a new orig_argv member to the PyConfig structure: the list of the original command line arguments passed to the Python executable. (Contributed by Victor Stinner in bpo-23427.)

Porting to Python 3.10

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

  • Since 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 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 bpo-39573.)

  • Since 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 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 bpo-39573.)

  • Since 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 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 bpo-39573.)

  • Calling PyDict_GetItem() without GIL held had been allowed for historical reason. It is no longer allowed. (Contributed by Victor Stinner in bpo-40839.)

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

Removed