What’s New In Python 3.11

Release

3.11.0a0

Date

September 04, 2021

This article explains the new features in Python 3.11, compared to 3.10.

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 3.11 moves towards release, so it’s worth checking back even after reading earlier versions.

Summary – Release highlights

New Features

Enhanced error locations in tracebacks

When printing tracebacks, the interpreter will now point to the exact expression that caused the error instead of just the line. For example:

Traceback (most recent call last):
  File "distance.py", line 11, in <module>
    print(manhattan_distance(p1, p2))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "distance.py", line 6, in manhattan_distance
    return abs(point_1.x - point_2.x) + abs(point_1.y - point_2.y)
                           ^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'x'

Previous versions of the interpreter would point to just the line making it ambiguous which object was None. These enhanced errors can also be helpful when dealing with deeply nested dictionary objects and multiple function calls,

Traceback (most recent call last):
  File "query.py", line 37, in <module>
    magic_arithmetic('foo')
    ^^^^^^^^^^^^^^^^^^^^^^^
  File "query.py", line 18, in magic_arithmetic
    return add_counts(x) / 25
           ^^^^^^^^^^^^^
  File "query.py", line 24, in add_counts
    return 25 + query_user(user1) + query_user(user2)
                ^^^^^^^^^^^^^^^^^
  File "query.py", line 32, in query_user
    return 1 + query_count(db, response['a']['b']['c']['user'], retry=True)
                               ~~~~~~~~~~~~~~~~~~^^^^^
TypeError: 'NoneType' object is not subscriptable

as well as complex arithmetic expressions:

Traceback (most recent call last):
  File "calculation.py", line 54, in <module>
    result = (x / y / z) * (a / b / c)
              ~~~~~~^~~
ZeroDivisionError: division by zero

See PEP 657 for more details. (Contributed by Pablo Galindo, Batuhan Taskaya and Ammar Askar in bpo-43950.)

Note

This feature requires storing column positions in code objects which may result in a small increase of disk usage of compiled Python files or interpreter memory usage. To avoid storing the extra information and/or deactivate printing the extra traceback information, the -X no_debug_ranges command line flag or the PYTHONNODEBUGRANGES environment variable can be used.

Column information for code objects

The information used by the enhanced traceback feature is made available as a general API that can be used to correlate bytecode instructions with source code. This information can be retrieved using:

The -X no_debug_ranges option and the environment variable PYTHONNODEBUGRANGES can be used to disable this feature.

See PEP 657 for more details. (Contributed by Pablo Galindo, Batuhan Taskaya and Ammar Askar in bpo-43950.)

Other Language Changes

Other CPython Implementation Changes

New Modules

  • None yet.

Improved Modules

fractions

Support PEP 515-style initialization of Fraction from string. (Contributed by Sergey B Kirpichev in bpo-44258.)

math

  • Add math.cbrt(): return the cube root of x. (Contributed by Ajith Ramachandran in bpo-44357.)

  • The behaviour of two math.pow() corner cases was changed, for consistency with the IEEE 754 specification. The operations math.pow(0.0, -math.inf) and math.pow(-0.0, -math.inf) now return inf. Previously they raised ValueError. (Contributed by Mark Dickinson in bpo-44339.)

os

  • On Windows, os.urandom() uses BCryptGenRandom() instead of CryptGenRandom() which is deprecated. (Contributed by Dong-hee Na in bpo-44611.)

sqlite3

Removed

  • smtpd.MailmanProxy is now removed as it is unusable without an external module, mailman. (Contributed by Dong-hee Na in bpo-35800.)

  • The binhex module, deprecated in Python 3.9, is now removed. The following binascii functions, deprecated in Python 3.9, are now also removed:

    • a2b_hqx(), b2a_hqx();

    • rlecode_hqx(), rledecode_hqx().

    The binascii.crc_hqx() function remains available.

    (Contributed by Victor Stinner in bpo-45085.)

Optimizations

  • Compiler now optimizes simple C-style formatting with literal format containing only format codes %s, %r and %a and makes it as fast as corresponding f-string expression. (Contributed by Serhiy Storchaka in bpo-28307.)

  • “Zero-cost” exceptions are implemented. The cost of try statements is almost eliminated when no exception is raised. (Contributed by Mark Shannon in bpo-40222.)

  • Method calls with keywords are now faster due to bytecode changes which avoid creating bound method instances. Previously, this optimization was applied only to method calls with purely positional arguments. (Contributed by Ken Jin and Mark Shannon in bpo-26110, based on ideas implemented in PyPy.)

  • .pdbrc is now read with 'utf-8' encoding.

CPython bytecode changes

Build Changes

Deprecated

  • The lib2to3 package is now deprecated and may not be able to parse Python 3.10 or newer. See the PEP 617 (New PEG parser for CPython). (Contributed by Victor Stinner in bpo-40360.)

Removed

  • The @asyncio.coroutine decorator enabling legacy generator-based coroutines to be compatible with async/await code. The function has been deprecated since Python 3.8 and the removal was initially scheduled for Python 3.10. Use async def instead. (Contributed by Illia Volochii in bpo-43216.)

  • asyncio.coroutines.CoroWrapper used for wrapping legacy generator-based coroutine objects in the debug mode. (Contributed by Illia Volochii in bpo-43216.)

Porting to Python 3.11

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

Changes in the Python API

C API Changes

New Features

Porting to Python 3.11

  • The old trashcan macros (Py_TRASHCAN_SAFE_BEGIN/Py_TRASHCAN_SAFE_END) are now deprecated. They should be replaced by the new macros Py_TRASHCAN_BEGIN and Py_TRASHCAN_END.

    A tp_dealloc function that has the old macros, such as:

    static void
mytype_dealloc(mytype *p)
{
    PyObject_GC_UnTrack(p);
    Py_TRASHCAN_SAFE_BEGIN(p);
    ...
    Py_TRASHCAN_SAFE_END
}

    should migrate to the new macros as follows:

    static void
mytype_dealloc(mytype *p)
{
    PyObject_GC_UnTrack(p);
    Py_TRASHCAN_BEGIN(p, mytype_dealloc)
    ...
    Py_TRASHCAN_END
}

    Note that Py_TRASHCAN_BEGIN has a second argument which should be the deallocation function it is in.

    To support older Python versions in the same codebase, you can define the following macros and use them throughout the code (credit: these were copied from the mypy codebase):

    #if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 8
#  define CPy_TRASHCAN_BEGIN(op, dealloc) Py_TRASHCAN_BEGIN(op, dealloc)
#  define CPy_TRASHCAN_END(op) Py_TRASHCAN_END
#else
#  define CPy_TRASHCAN_BEGIN(op, dealloc) Py_TRASHCAN_SAFE_BEGIN(op)
#  define CPy_TRASHCAN_END(op) Py_TRASHCAN_SAFE_END(op)
#endif

  • The PyType_Ready() function now raises an error if a type is defined with the Py_TPFLAGS_HAVE_GC flag set but has no traverse function (PyTypeObject.tp_traverse). (Contributed by Victor Stinner in bpo-44263.)

  • Heap types with the Py_TPFLAGS_IMMUTABLETYPE flag can now inherit the PEP 590 vectorcall protocol. Previously, this was only possible for static types. (Contributed by Erlend E. Aasland in bpo-43908)

Deprecated

Removed