What’s New In Python 3.11¶

PEP 657: Fine-grained 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 dict 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

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

• The codeobject.co_positions() method in Python.

• The PyCode_Addr2Location() function in the C API.

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

PEP 654: Exception Groups and except*¶

PEP 654 introduces language features that enable a program to raise and handle multiple unrelated exceptions simultaneously. The builtin types ExceptionGroup and BaseExceptionGroup make it possible to group exceptions and raise them together, and the new except* syntax generalizes except to match subgroups of exception groups.

See PEP 654 for more details.

(Contributed by Irit Katriel in bpo-45292. PEP written by Irit Katriel, Yury Selivanov and Guido van Rossum.)

PEP 678: Exceptions can be enriched with notes¶

The add_note() method is added to BaseException. It can be used to enrich exceptions with context information that is not available at the time when the exception is raised. The added notes appear in the default traceback.

See PEP 678 for more details.

(Contributed by Irit Katriel in bpo-45607. PEP written by Zac Hatfield-Dodds.)

Windows py.exe launcher improvements¶

The copy of the Python install manager included with Python 3.11 has been significantly updated. It now supports company/tag syntax as defined in PEP 514 using the -V:<company>/<tag> argument instead of the limited -<major>.<minor>. This allows launching distributions other than PythonCore, the one hosted on python.org.

When using -V: selectors, either company or tag can be omitted, but all installs will be searched. For example, -V:OtherPython/ will select the “best” tag registered for OtherPython, while -V:3.11 or -V:/3.11 will select the “best” distribution with tag 3.11.

When using the legacy -<major>, -<major>.<minor>, -<major>-<bitness> or -<major>.<minor>-<bitness> arguments, all existing behaviour should be preserved from past versions, and only releases from PythonCore will be selected. However, the -64 suffix now implies “not 32-bit” (not necessarily x86-64), as there are multiple supported 64-bit platforms. 32-bit runtimes are detected by checking the runtime’s tag for a -32 suffix. All releases of Python since 3.5 have included this in their 32-bit builds.

PEP 646: Variadic generics¶

PEP 484 previously introduced TypeVar, enabling creation of generics parameterised with a single type. PEP 646 adds TypeVarTuple, enabling parameterisation with an arbitrary number of types. In other words, a TypeVarTuple is a variadic type variable, enabling variadic generics.

This enables a wide variety of use cases. In particular, it allows the type of array-like structures in numerical computing libraries such as NumPy and TensorFlow to be parameterised with the array shape. Static type checkers will now be able to catch shape-related bugs in code that uses these libraries.

See PEP 646 for more details.

(Contributed by Matthew Rahtz in bpo-43224, with contributions by Serhiy Storchaka and Jelle Zijlstra. PEP written by Mark Mendoza, Matthew Rahtz, Pradeep Kumar Srinivasan, and Vincent Siles.)

PEP 655: Marking individual TypedDict items as required or not-required¶

Required and NotRequired provide a straightforward way to mark whether individual items in a TypedDict must be present. Previously, this was only possible using inheritance.

All fields are still required by default, unless the total parameter is set to False, in which case all fields are still not-required by default. For example, the following specifies a TypedDict with one required and one not-required key:

class Movie(TypedDict):
   title: str
   year: NotRequired[int]

m1: Movie = {"title": "Black Panther", "year": 2018}  # OK
m2: Movie = {"title": "Star Wars"}  # OK (year is not required)
m3: Movie = {"year": 2022}  # ERROR (missing required field title)

The following definition is equivalent:

class Movie(TypedDict, total=False):
   title: Required[str]
   year: int

See PEP 655 for more details.

(Contributed by David Foster and Jelle Zijlstra in bpo-47087. PEP written by David Foster.)

PEP 673: Self type¶

The new Self annotation provides a simple and intuitive way to annotate methods that return an instance of their class. This behaves the same as the TypeVar-based approach specified in PEP 484, but is more concise and easier to follow.

Common use cases include alternative constructors provided as classmethods, and __enter__() methods that return self:

class MyLock:
    def __enter__(self) -> Self:
        self.lock()
        return self

    ...

class MyInt:
    @classmethod
    def fromhex(cls, s: str) -> Self:
        return cls(int(s, 16))

    ...

Self can also be used to annotate method parameters or attributes of the same type as their enclosing class.

See PEP 673 for more details.

(Contributed by James Hilton-Balfe in bpo-46534. PEP written by Pradeep Kumar Srinivasan and James Hilton-Balfe.)

PEP 675: Arbitrary literal string type¶

The new LiteralString annotation may be used to indicate that a function parameter can be of any literal string type. This allows a function to accept arbitrary literal string types, as well as strings created from other literal strings. Type checkers can then enforce that sensitive functions, such as those that execute SQL statements or shell commands, are called only with static arguments, providing protection against injection attacks.

For example, a SQL query function could be annotated as follows:

def run_query(sql: LiteralString) -> ...
    ...

def caller(
    arbitrary_string: str,
    query_string: LiteralString,
    table_name: LiteralString,
) -> None:
    run_query("SELECT * FROM students")       # ok
    run_query(query_string)                   # ok
    run_query("SELECT * FROM " + table_name)  # ok
    run_query(arbitrary_string)               # type checker error
    run_query(                                # type checker error
        f"SELECT * FROM students WHERE name = {arbitrary_string}"
    )

See PEP 675 for more details.

(Contributed by Jelle Zijlstra in bpo-47088. PEP written by Pradeep Kumar Srinivasan and Graham Bleaney.)

PEP 681: Data class transforms¶

dataclass_transform may be used to decorate a class, metaclass, or a function that is itself a decorator. The presence of @dataclass_transform() tells a static type checker that the decorated object performs runtime “magic” that transforms a class, giving it dataclass-like behaviors.

For example:

# The create_model decorator is defined by a library.
@typing.dataclass_transform()
def create_model(cls: Type[T]) -> Type[T]:
    cls.__init__ = ...
    cls.__eq__ = ...
    cls.__ne__ = ...
    return cls

# The create_model decorator can now be used to create new model classes:
@create_model
class CustomerModel:
    id: int
    name: str

c = CustomerModel(id=327, name="Eric Idle")

See PEP 681 for more details.

(Contributed by Jelle Zijlstra in gh-91860. PEP written by Erik De Bonte and Eric Traut.)

PEP 563 may not be the future¶

PEP 563 Postponed Evaluation of Annotations (the from __future__ import annotations future statement) that was originally planned for release in Python 3.10 has been put on hold indefinitely. See this message from the Steering Council for more information.

asyncio¶

• Added the TaskGroup class, an asynchronous context manager holding a group of tasks that will wait for all of them upon exit. For new code this is recommended over using create_task() and gather() directly. (Contributed by Yury Selivanov and others in gh-90908.)

• Added timeout(), an asynchronous context manager for setting a timeout on asynchronous operations. For new code this is recommended over using wait_for() directly. (Contributed by Andrew Svetlov in gh-90927.)

• Added the Runner class, which exposes the machinery used by run(). (Contributed by Andrew Svetlov in gh-91218.)

• Added the Barrier class to the synchronization primitives in the asyncio library, and the related BrokenBarrierError exception. (Contributed by Yves Duprat and Andrew Svetlov in gh-87518.)

• Added keyword argument all_errors to asyncio.loop.create_connection() so that multiple connection errors can be raised as an ExceptionGroup.

• Added the asyncio.StreamWriter.start_tls() method for upgrading existing stream-based connections to TLS. (Contributed by Ian Good in bpo-34975.)

• Added raw datagram socket functions to the event loop: sock_sendto(), sock_recvfrom() and sock_recvfrom_into(). These have implementations in SelectorEventLoop and ProactorEventLoop. (Contributed by Alex Grönholm in bpo-46805.)

• Added cancelling() and uncancel() methods to Task. These are primarily intended for internal use, notably by TaskGroup.

contextlib¶

• Added non parallel-safe chdir() context manager to change the current working directory and then restore it on exit. Simple wrapper around chdir(). (Contributed by Filipe Laíns in bpo-25625)

dataclasses¶

• Change field default mutability check, allowing only defaults which are hashable instead of any object which is not an instance of dict, list or set. (Contributed by Eric V. Smith in bpo-44674.)

datetime¶

• Add datetime.UTC, a convenience alias for datetime.timezone.utc. (Contributed by Kabir Kwatra in gh-91973.)

• datetime.date.fromisoformat(), datetime.time.fromisoformat() and datetime.datetime.fromisoformat() can now be used to parse most ISO 8601 formats (barring only those that support fractional hours and minutes). (Contributed by Paul Ganssle in gh-80010.)

enum¶

• Renamed EnumMeta to EnumType (EnumMeta kept as an alias).

• Added StrEnum, with members that can be used as (and must be) strings.

• Added ReprEnum, which only modifies the __repr__() of members while returning their literal values (rather than names) for __str__() and __format__() (used by str(), format() and f-strings).

• Changed Enum.__format__() (the default for format(), str.format() and f-strings) to always produce the same result as Enum.__str__(): for enums inheriting from ReprEnum it will be the member’s value; for all other enums it will be the enum and member name (e.g. Color.RED).

• Added a new boundary class parameter to Flag enums and the FlagBoundary enum with its options, to control how to handle out-of-range flag values.

• Added the verify() enum decorator and the EnumCheck enum with its options, to check enum classes against several specific constraints.

• Added the member() and nonmember() decorators, to ensure the decorated object is/is not converted to an enum member.

• Added the property() decorator, which works like property() except for enums. Use this instead of types.DynamicClassAttribute().

• Added the global_enum() enum decorator, which adjusts __repr__() and __str__() to show values as members of their module rather than the enum class. For example, 're.ASCII' for the ASCII member of re.RegexFlag rather than 'RegexFlag.ASCII'.

• Enhanced Flag to support len(), iteration and in/not in on its members. For example, the following now works: len(AFlag(3)) == 2 and list(AFlag(3)) == (AFlag.ONE, AFlag.TWO)

• Changed Enum and Flag so that members are now defined before __init_subclass__() is called; dir() now includes methods, etc., from mixed-in data types.

• Changed Flag to only consider primary values (power of two) canonical while composite values (3, 6, 10, etc.) are considered aliases; inverted flags are coerced to their positive equivalent.

fcntl¶

• On FreeBSD, the F_DUP2FD and F_DUP2FD_CLOEXEC flags respectively are supported, the former equals to dup2 usage while the latter set the FD_CLOEXEC flag in addition.

fractions¶

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

• Fraction now implements an __int__ method, so that an isinstance(some_fraction, typing.SupportsInt) check passes. (Contributed by Mark Dickinson in bpo-44547.)

functools¶

• functools.singledispatch() now supports types.UnionType and typing.Union as annotations to the dispatch argument.:

  >>> from functools import singledispatch
  >>> @singledispatch
  ... def fun(arg, verbose=False):
  ...     if verbose:
  ...         print("Let me just say,", end=" ")
  ...     print(arg)
  ...
  >>> @fun.register
  ... def _(arg: int | float, verbose=False):
  ...     if verbose:
  ...         print("Strength in numbers, eh?", end=" ")
  ...     print(arg)
  ...
  >>> from typing import Union
  >>> @fun.register
  ... def _(arg: Union[list, set], verbose=False):
  ...     if verbose:
  ...         print("Enumerate this:")
  ...     for i, elem in enumerate(arg):
  ...         print(i, elem)
  ...
  

  (Contributed by Yurii Karabas in bpo-46014.)

gzip¶

• The gzip.compress() function is now faster when used with the mtime=0 argument as it delegates the compression entirely to a single zlib.compress() operation. There is one side effect of this change: The gzip file header contains an “OS” byte in its header. That was traditionally always set to a value of 255 representing “unknown” by the gzip module. Now, when using compress() with mtime=0, it may be set to a different value by the underlying zlib C library Python was linked against. (See gh-112346 for details on the side effect.)

hashlib¶

• hashlib.blake2b() and hashlib.blake2s() now prefer libb2 over Python’s vendored copy. (Contributed by Christian Heimes in bpo-47095.)

• The internal _sha3 module with SHA3 and SHAKE algorithms now uses tiny_sha3 instead of the Keccak Code Package to reduce code and binary size. The hashlib module prefers optimized SHA3 and SHAKE implementations from OpenSSL. The change affects only installations without OpenSSL support. (Contributed by Christian Heimes in bpo-47098.)

• Add hashlib.file_digest(), a helper function for efficient hashing of files or file-like objects. (Contributed by Christian Heimes in gh-89313.)

IDLE and idlelib¶

• Apply syntax highlighting to .pyi files. (Contributed by Alex Waygood and Terry Jan Reedy in bpo-45447.)

• Include prompts when saving Shell with inputs and outputs. (Contributed by Terry Jan Reedy in gh-95191.)

inspect¶

• Add getmembers_static() to return all members without triggering dynamic lookup via the descriptor protocol. (Contributed by Weipeng Hong in bpo-30533.)

• Add ismethodwrapper() for checking if the type of an object is a MethodWrapperType. (Contributed by Hakan Çelik in bpo-29418.)

• Change the frame-related functions in the inspect module to return new FrameInfo and Traceback class instances (backwards compatible with the previous named tuple-like interfaces) that includes the extended PEP 657 position information (end line number, column and end column). The affected functions are:

  • inspect.getframeinfo()

  • inspect.getouterframes()

  • inspect.getinnerframes(),

  • inspect.stack()

  • inspect.trace()

  (Contributed by Pablo Galindo in gh-88116.)

locale¶

• Add locale.getencoding() to get the current locale encoding. It is similar to locale.getpreferredencoding(False) but ignores the Python UTF-8 Mode.

logging¶

• Added getLevelNamesMapping() to return a mapping from logging level names (e.g. 'CRITICAL') to the values of their corresponding Logging Levels (e.g. 50, by default). (Contributed by Andrei Kulakovin in gh-88024.)

• Added a createSocket() method to SysLogHandler, to match SocketHandler.createSocket(). It is called automatically during handler initialization and when emitting an event, if there is no active socket. (Contributed by Kirill Pinchuk in gh-88457.)

math¶

• Add math.exp2(): return 2 raised to the power of x. (Contributed by Gideon Mitchell in bpo-45917.)

• 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.)

• The math.nan value is now always available. (Contributed by Victor Stinner in bpo-46917.)

operator¶

• A new function operator.call has been added, such that operator.call(obj, *args, **kwargs) == obj(*args, **kwargs). (Contributed by Antony Lee in bpo-44019.)

os¶

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

pathlib¶

• glob() and rglob() return only directories if pattern ends with a pathname components separator: sep or altsep. (Contributed by Eisuke Kawasima in bpo-22276 and bpo-33392.)

re¶

• Atomic grouping ((?>...)) and possessive quantifiers (*+, ++, ?+, {m,n}+) are now supported in regular expressions. (Contributed by Jeffrey C. Jacobs and Serhiy Storchaka in bpo-433030.)

shutil¶

• Add optional parameter dir_fd in shutil.rmtree(). (Contributed by Serhiy Storchaka in bpo-46245.)

socket¶

• Add CAN Socket support for NetBSD. (Contributed by Thomas Klausner in bpo-30512.)

• create_connection() has an option to raise, in case of failure to connect, an ExceptionGroup containing all errors instead of only raising the last error. (Contributed by Irit Katriel in bpo-29980.)

sqlite3¶

• You can now disable the authorizer by passing None to set_authorizer(). (Contributed by Erlend E. Aasland in bpo-44491.)

• Collation name create_collation() can now contain any Unicode character. Collation names with invalid characters now raise UnicodeEncodeError instead of sqlite3.ProgrammingError. (Contributed by Erlend E. Aasland in bpo-44688.)

• sqlite3 exceptions now include the SQLite extended error code as sqlite_errorcode and the SQLite error name as sqlite_errorname. (Contributed by Aviv Palivoda, Daniel Shahaf, and Erlend E. Aasland in bpo-16379 and bpo-24139.)

• Add setlimit() and getlimit() to sqlite3.Connection for setting and getting SQLite limits by connection basis. (Contributed by Erlend E. Aasland in bpo-45243.)

• sqlite3 now sets sqlite3.threadsafety based on the default threading mode the underlying SQLite library has been compiled with. (Contributed by Erlend E. Aasland in bpo-45613.)

• sqlite3 C callbacks now use unraisable exceptions if callback tracebacks are enabled. Users can now register an unraisable hook handler to improve their debug experience. (Contributed by Erlend E. Aasland in bpo-45828.)

• Fetch across rollback no longer raises InterfaceError. Instead we leave it to the SQLite library to handle these cases. (Contributed by Erlend E. Aasland in bpo-44092.)

• Add serialize() and deserialize() to sqlite3.Connection for serializing and deserializing databases. (Contributed by Erlend E. Aasland in bpo-41930.)

• Add create_window_function() to sqlite3.Connection for creating aggregate window functions. (Contributed by Erlend E. Aasland in bpo-34916.)

• Add blobopen() to sqlite3.Connection. sqlite3.Blob allows incremental I/O operations on blobs. (Contributed by Aviv Palivoda and Erlend E. Aasland in bpo-24905.)

string¶

• Add get_identifiers() and is_valid() to string.Template, which respectively return all valid placeholders, and whether any invalid placeholders are present. (Contributed by Ben Kehoe in gh-90465.)

sys¶

• sys.exc_info() now derives the type and traceback fields from the value (the exception instance), so when an exception is modified while it is being handled, the changes are reflected in the results of subsequent calls to exc_info(). (Contributed by Irit Katriel in bpo-45711.)

• Add sys.exception() which returns the active exception instance (equivalent to sys.exc_info()[1]). (Contributed by Irit Katriel in bpo-46328.)

• Add the sys.flags.safe_path flag. (Contributed by Victor Stinner in gh-57684.)

sysconfig¶

• Three new installation schemes (posix_venv, nt_venv and venv) were added and are used when Python creates new virtual environments or when it is running from a virtual environment. The first two schemes (posix_venv and nt_venv) are OS-specific for non-Windows and Windows, the venv is essentially an alias to one of them according to the OS Python runs on. This is useful for downstream distributors who modify sysconfig.get_preferred_scheme(). Third party code that creates new virtual environments should use the new venv installation scheme to determine the paths, as does venv. (Contributed by Miro Hrončok in bpo-45413.)

tempfile¶

• SpooledTemporaryFile objects now fully implement the methods of io.BufferedIOBase or io.TextIOBase (depending on file mode). This lets them work correctly with APIs that expect file-like objects, such as compression modules. (Contributed by Carey Metcalfe in gh-70363.)

threading¶

• On Unix, if the sem_clockwait() function is available in the C library (glibc 2.30 and newer), the threading.Lock.acquire() method now uses the monotonic clock (time.CLOCK_MONOTONIC) for the timeout, rather than using the system clock (time.CLOCK_REALTIME), to not be affected by system clock changes. (Contributed by Victor Stinner in bpo-41710.)

time¶

• On Unix, time.sleep() now uses the clock_nanosleep() or nanosleep() function, if available, which has a resolution of 1 nanosecond (10^-9 seconds), rather than using select() which has a resolution of 1 microsecond (10^-6 seconds). (Contributed by Benjamin Szőke and Victor Stinner in bpo-21302.)

• On Windows 8.1 and newer, time.sleep() now uses a waitable timer based on high-resolution timers which has a resolution of 100 nanoseconds (10^-7 seconds). Previously, it had a resolution of 1 millisecond (10^-3 seconds). (Contributed by Benjamin Szőke, Donghee Na, Eryk Sun and Victor Stinner in bpo-21302 and bpo-45429.)

tkinter¶

• Added method info_patchlevel() which returns the exact version of the Tcl library as a named tuple similar to sys.version_info. (Contributed by Serhiy Storchaka in gh-91827.)

traceback¶

• Add traceback.StackSummary.format_frame_summary() to allow users to override which frames appear in the traceback, and how they are formatted. (Contributed by Ammar Askar in bpo-44569.)

• Add traceback.TracebackException.print(), which prints the formatted TracebackException instance to a file. (Contributed by Irit Katriel in bpo-33809.)

typing¶

For major changes, see New Features Related to Type Hints.

• Add typing.assert_never() and typing.Never. typing.assert_never() is useful for asking a type checker to confirm that a line of code is not reachable. At runtime, it raises an AssertionError. (Contributed by Jelle Zijlstra in gh-90633.)

• Add typing.reveal_type(). This is useful for asking a type checker what type it has inferred for a given expression. At runtime it prints the type of the received value. (Contributed by Jelle Zijlstra in gh-90572.)

• Add typing.assert_type(). This is useful for asking a type checker to confirm that the type it has inferred for a given expression matches the given type. At runtime it simply returns the received value. (Contributed by Jelle Zijlstra in gh-90638.)

• typing.TypedDict types can now be generic. (Contributed by Samodya Abeysiriwardane in gh-89026.)

• NamedTuple types can now be generic. (Contributed by Serhiy Storchaka in bpo-43923.)

• Allow subclassing of typing.Any. This is useful for avoiding type checker errors related to highly dynamic class, such as mocks. (Contributed by Shantanu Jain in gh-91154.)

• The typing.final() decorator now sets the __final__ attributed on the decorated object. (Contributed by Jelle Zijlstra in gh-90500.)

• The typing.get_overloads() function can be used for introspecting the overloads of a function. typing.clear_overloads() can be used to clear all registered overloads of a function. (Contributed by Jelle Zijlstra in gh-89263.)

• The __init__() method of Protocol subclasses is now preserved. (Contributed by Adrian Garcia Badarasco in gh-88970.)

• The representation of empty tuple types (Tuple[()]) is simplified. This affects introspection, e.g. get_args(Tuple[()]) now evaluates to () instead of ((),). (Contributed by Serhiy Storchaka in gh-91137.)

• Loosen runtime requirements for type annotations by removing the callable check in the private typing._type_check function. (Contributed by Gregory Beauregard in gh-90802.)

• typing.get_type_hints() now supports evaluating strings as forward references in PEP 585 generic aliases. (Contributed by Niklas Rosenstein in gh-85542.)

• typing.get_type_hints() no longer adds Optional to parameters with None as a default. (Contributed by Nikita Sobolev in gh-90353.)

• typing.get_type_hints() now supports evaluating bare stringified ClassVar annotations. (Contributed by Gregory Beauregard in gh-90711.)

• typing.no_type_check() no longer modifies external classes and functions. It also now correctly marks classmethods as not to be type checked. (Contributed by Nikita Sobolev in gh-90729.)

unicodedata¶

• The Unicode database has been updated to version 14.0.0. (Contributed by Benjamin Peterson in bpo-45190).

unittest¶

• Added methods enterContext() and enterClassContext() of class TestCase, method enterAsyncContext() of class IsolatedAsyncioTestCase and function unittest.enterModuleContext(). (Contributed by Serhiy Storchaka in bpo-45046.)

venv¶

• When new Python virtual environments are created, the venv sysconfig installation scheme is used to determine the paths inside the environment. When Python runs in a virtual environment, the same installation scheme is the default. That means that downstream distributors can change the default sysconfig install scheme without changing behavior of virtual environments. Third party code that also creates new virtual environments should do the same. (Contributed by Miro Hrončok in bpo-45413.)

warnings¶

• warnings.catch_warnings() now accepts arguments for warnings.simplefilter(), providing a more concise way to locally ignore warnings or convert them to errors. (Contributed by Zac Hatfield-Dodds in bpo-47074.)

zipfile¶

• Added support for specifying member name encoding for reading metadata in a ZipFile’s directory and file headers. (Contributed by Stephen J. Turnbull and Serhiy Storchaka in bpo-28080.)

• Added ZipFile.mkdir() for creating new directories inside ZIP archives. (Contributed by Sam Ezeh in gh-49083.)

• Added stem, suffix and suffixes to zipfile.Path. (Contributed by Miguel Brito in gh-88261.)

Faster Startup¶

Read __pycache__ -> Unmarshal -> Heap allocated code object -> Evaluate

Statically allocated code object -> Evaluate

Faster Runtime¶

Misc¶

• Objects now require less memory due to lazily created object namespaces. Their namespace dictionaries now also share keys more freely. (Contributed Mark Shannon in bpo-45340 and bpo-40116.)

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

• A more concise representation of exceptions in the interpreter reduced the time required for catching an exception by about 10%. (Contributed by Irit Katriel in bpo-45711.)

• re’s regular expression matching engine has been partially refactored, and now uses computed gotos (or “threaded code”) on supported platforms. As a result, Python 3.11 executes the pyperformance regular expression benchmarks up to 10% faster than Python 3.10. (Contributed by Brandt Bucher in gh-91404.)

FAQ¶

About¶

Faster CPython explores optimizations for CPython. The main team is funded by Microsoft to work on this full-time. Pablo Galindo Salgado is also funded by Bloomberg LP to work on the project part-time. Finally, many contributors are volunteers from the community.

New opcodes¶

• ASYNC_GEN_WRAP, RETURN_GENERATOR and SEND, used in generators and co-routines.

• COPY_FREE_VARS, which avoids needing special caller-side code for closures.

• JUMP_BACKWARD_NO_INTERRUPT, for use in certain loops where handling interrupts is undesirable.

• MAKE_CELL, to create Cell Objects.

• CHECK_EG_MATCH and PREP_RERAISE_STAR, to handle the new exception groups and except* added in PEP 654.

• PUSH_EXC_INFO, for use in exception handlers.

• RESUME, a no-op, for internal tracing, debugging and optimization checks.

Replaced opcodes¶

Changed/removed opcodes¶

• Changed MATCH_CLASS and MATCH_KEYS to no longer push an additional boolean value to indicate success/failure. Instead, None is pushed on failure in place of the tuple of extracted values.

• Changed opcodes that work with exceptions to reflect them now being represented as one item on the stack instead of three (see gh-89874).

• Removed COPY_DICT_WITHOUT_KEYS, GEN_START, POP_BLOCK, SETUP_FINALLY and YIELD_FROM.

Language/Builtins¶

• Chaining classmethod descriptors (introduced in bpo-19072) is now deprecated. It can no longer be used to wrap other descriptors such as property. The core design of this feature was flawed and caused a number of downstream problems. To “pass-through” a classmethod, consider using the __wrapped__ attribute that was added in Python 3.10. (Contributed by Raymond Hettinger in