What’s New In Python 3.11

Release

3.11.0rc2

Date

September 29, 2022

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

For full details, see the changelog.

Summary – Release highlights

  • Python 3.11 is between 10-60% faster than Python 3.10. On average, we measured a 1.25x speedup on the standard benchmark suite. See Faster CPython for details.

New syntax features:

  • PEP 654: Exception Groups and except*.

New built-in features:

  • PEP 678: Enriching Exceptions with Notes.

New standard library modules:

  • PEP 680: tomllib — Support for Parsing TOML in the Standard Library.

Interpreter improvements:

  • PEP 657: Include Fine Grained Error Locations in Tracebacks.

  • New -P command line option and PYTHONSAFEPATH environment variable to disable automatically prepending a potentially unsafe path (the working dir or script directory, depending on invocation) to sys.path.

New typing features:

  • PEP 646: Variadic generics.

  • PEP 655: Marking individual TypedDict items as required or potentially missing.

  • PEP 673: Self type.

  • PEP 675: Arbitrary literal string type.

  • PEP 681: Data Class Transforms.

Important deprecations, removals or restrictions:

  • PEP 594: Removing dead batteries from the standard library.

  • PEP 624: Remove Py_UNICODE encoder APIs.

  • PEP 670: Convert macros to functions in the Python C API.

New Features

PEP 657: 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 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:

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 in interpreter memory usage and disk usage for compiled Python files. To avoid storing the extra information and deactivate printing the extra traceback information, use the -X no_debug_ranges command line option or the PYTHONNODEBUGRANGES environment variable.

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.)

Other Language Changes

Other CPython Implementation Changes

  • Special methods complex.__complex__() and bytes.__bytes__() are implemented to support typing.SupportsComplex and typing.SupportsBytes protocols. (Contributed by Mark Dickinson and Dong-hee Na in bpo-24234.)

  • siphash13 is added as a new internal hashing algorithms. It has similar security properties as siphash24 but it is slightly faster for long inputs. str, bytes, and some other types now use it as default algorithm for hash(). PEP 552 hash-based pyc files now use siphash13, too. (Contributed by Inada Naoki in bpo-29410.)

  • When an active exception is re-raised by a raise statement with no parameters, the traceback attached to this exception is now always sys.exc_info()[1].__traceback__. This means that changes made to the traceback in the current except clause are reflected in the re-raised exception. (Contributed by Irit Katriel in bpo-45711.)

  • The interpreter state’s representation of handled exceptions (a.k.a exc_info, or _PyErr_StackItem) now has only the exc_value field, exc_type and exc_traceback have been removed as their values can be derived from exc_value. (Contributed by Irit Katriel in bpo-45711.)

  • A new command line option for the Windows installer AppendPath has been added. It behaves similiar to PrependPath but appends the install and scripts directories instead of prepending them. (Contributed by Bastian Neuburger in bpo-44934.)

  • The PyConfig.module_search_paths_set field must now be set to 1 for initialization to use PyConfig.module_search_paths to initialize sys.path. Otherwise, initialization will recalculate the path and replace any values added to module_search_paths.

  • The output of the --help option is changed to fit inside 50 lines and 80 columns. Information about Python environment variables and -X options is available with the new --help-env or --help-xoptions flags, and with --help-all. (Contributed by Éric Araujo in bpo-46142.)

  • Converting between int and str in bases other than 2 (binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now raises a ValueError if the number of digits in string form is above a limit to avoid potential denial of service attacks due to the algorithmic complexity. This is a mitigation for CVE-2020-10735. This limit can be configured or disabled by environment variable, command line flag, or sys APIs. See the integer string conversion length limitation documentation. The default limit is 4300 digits in string form.

New Modules

  • A new module, tomllib, was added for parsing TOML. (Contributed by Taneli Hukkinen in bpo-40059.)

  • wsgiref.types, containing WSGI-specific types for static type checking, was added. (Contributed by Sebastian Rittau in bpo-42012.)

Improved Modules

asyncio

  • Add raw datagram socket functions to the event loop: sock_sendto(), sock_recvfrom() and sock_recvfrom_into(). (Contributed by Alex Grönholm in bpo-46805.)

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

  • Add Barrier class to the synchronization primitives of the asyncio library. (Contributed by Yves Duprat and Andrew Svetlov in gh-87518.)

  • Add TaskGroup class, an asynchronous context manager holding a group of tasks that will wait for all of them upon exit. (Contributed by Yury Seliganov and others.)

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

enum

  • EnumMeta renamed to EnumType (EnumMeta kept as alias).

  • StrEnum added – enum members are and must be strings.

  • ReprEnum added – causes only the __repr__ to be modified, not the __str__ nor the __format__.

  • FlagBoundary added – controls behavior when invalid values are given to a flag.

  • EnumCheck added – used by verify to ensure various constraints.

  • verify added – function to ensure given EnumCheck constraints.

  • member added – decorator to ensure given object is converted to an enum member.

  • nonmember added – decorator to ensure given object is not converted to an enum member.

  • property added – use instead of types.DynamicClassAttribute.

  • global_enum added – enum decorator to adjust __repr__ and __str__ to show members in the global context – see re.RegexFlag for an example.

  • Flag enhancements: members support length, iteration, and containment checks.

  • Enum/Flag fixes: members are now defined before __init_subclass__ is called; dir() now includes methods, etc., from mixed-in data types.

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

  • IntEnum / IntFlag / StrEnum fixes: these now inherit from ReprEnum so the str() output now matches format() output, which is the data types’ (so both str(AnIntEnum.ONE) and format(AnIntEnum.ONE) is equal to '1').

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.)

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

locale

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 Dong-hee Na in bpo-44611.)

pathlib

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

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

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.)

threading

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, Dong-hee Na, Eryk Sun and Victor Stinner in bpo-21302 and bpo-45429.)

traceback

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.)

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.)

unicodedata

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

unittest

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

zipfile

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

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.

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.)

  • Pure ASCII strings are now normalized in constant time by unicodedata.normalize(). (Contributed by Dong-hee Na in bpo-44987.)

  • math functions comb() and perm() are now up to 10 times or more faster for large arguments (the speed up is larger for larger k). (Contributed by Serhiy Storchaka in bpo-37295.)

  • Dict don’t store hash value when all inserted keys are Unicode objects. This reduces dict size. For example, sys.getsizeof(dict.fromkeys("abcdefg")) becomes 272 bytes from 352 bytes on 64bit platform. (Contributed by Inada Naoki in bpo-46845.)

  • 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.

Faster CPython

CPython 3.11 is on average 25% faster than CPython 3.10 when measured with the pyperformance benchmark suite, and compiled with GCC on Ubuntu Linux. Depending on your workload, the speedup could be up to 10-60% faster.

This project focuses on two major areas in Python: faster startup and faster runtime. Other optimizations not under this project are listed in Optimizations.

Faster Startup

Frozen imports / Static code objects

Python caches bytecode in the __pycache__ directory to speed up module loading.

Previously in 3.10, Python module execution looked like this:

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

In Python 3.11, the core modules essential for Python startup are “frozen”. This means that their code objects (and bytecode) are statically allocated by the interpreter. This reduces the steps in module execution process to this:

Statically allocated code object -> Evaluate

Interpreter startup is now 10-15% faster in Python 3.11. This has a big impact for short-running programs using Python.

(Contributed by Eric Snow, Guido van Rossum and Kumar Aditya in numerous issues.)

Faster Runtime

Cheaper, lazy Python frames

Python frames are created whenever Python calls a Python function. This frame holds execution information. The following are new frame optimizations:

  • Streamlined the frame creation process.

  • Avoided memory allocation by generously re-using frame space on the C stack.

  • Streamlined the internal frame struct to contain only essential information. Frames previously held extra debugging and memory management information.

Old-style frame objects are now created only when requested by debuggers or by Python introspection functions such as sys._getframe or inspect.currentframe. For most user code, no frame objects are created at all. As a result, nearly all Python functions calls have sped up significantly. We measured a 3-7% speedup in pyperformance.

(Contributed by Mark Shannon in bpo-44590.)

Inlined Python function calls

During a Python function call, Python will call an evaluating C function to interpret that function’s code. This effectively limits pure Python recursion to what’s safe for the C stack.

In 3.11, when CPython detects Python code calling another Python function, it sets up a new frame, and “jumps” to the new code inside the new frame. This avoids calling the C interpreting function altogether.

Most Python function calls now consume no C stack space. This speeds up most of such calls. In simple recursive functions like fibonacci or factorial, a 1.7x speedup was observed. This also means recursive functions can recurse significantly deeper (if the user increases the recursion limit). We measured a 1-3% improvement in pyperformance.

(Contributed by Pablo Galindo and Mark Shannon in bpo-45256.)

PEP 659: Specializing Adaptive Interpreter

PEP 659 is one of the key parts of the faster CPython project. The general idea is that while Python is a dynamic language, most code has regions where objects and types rarely change. This concept is known as type stability.

At runtime, Python will try to look for common patterns and type stability in the executing code. Python will then replace the current operation with a more specialized one. This specialized operation uses fast paths available only to those use cases/types, which generally outperform their generic counterparts. This also brings in another concept called inline caching, where Python caches the results of expensive operations directly in the bytecode.

The specializer will also combine certain common instruction pairs into one superinstruction. This reduces the overhead during execution.

Python will only specialize when it sees code that is “hot” (executed multiple times). This prevents Python from wasting time for run-once code. Python can also de-specialize when code is too dynamic or when the use changes. Specialization is attempted periodically, and specialization attempts are not too expensive. This allows specialization to adapt to new circumstances.

(PEP written by Mark Shannon, with ideas inspired by Stefan Brunthaler. See PEP 659 for more information. Implementation by Mark Shannon and Brandt Bucher, with additional help from Irit Katriel and Dennis Sweeney.)

Operation

Form

Specialization

Operation speedup (up to)

Contributor(s)

Binary operations

x+x; x*x; x-x;

Binary add, multiply and subtract for common types such as int, float, and str take custom fast paths for their underlying types.

10%

Mark Shannon, Dong-hee Na, Brandt Bucher, Dennis Sweeney

Subscript

a[i]

Subscripting container types such as list, tuple and dict directly index the underlying data structures.

Subscripting custom __getitem__ is also inlined similar to Inlined Python function calls.

10-25%

Irit Katriel, Mark Shannon

Store subscript

a[i] = z

Similar to subscripting specialization above.

10-25%

Dennis Sweeney

Calls

f(arg) C(arg)

Calls to common builtin (C) functions and types such as len and str directly call their underlying C version. This avoids going through the internal calling convention.

20%

Mark Shannon, Ken Jin

Load global variable

print len

The object’s index in the globals/builtins namespace is cached. Loading globals and builtins require zero namespace lookups.

1

Mark Shannon

Load attribute

o.attr

Similar to loading global variables. The attribute’s index inside the class/object’s namespace is cached. In most cases, attribute loading will require zero namespace lookups.

2

Mark Shannon

Load methods for call

o.meth()

The actual address of the method is cached. Method loading now has no namespace lookups – even for classes with long inheritance chains.

10-20%

Ken Jin, Mark Shannon

Store attribute

o.attr = z

Similar to load attribute optimization.

2% in pyperformance

Mark Shannon

Unpack Sequence

*seq

Specialized for common containers such as list and tuple. Avoids internal calling convention.

8%

Brandt Bucher

1

A similar optimization already existed since Python 3.8. 3.11 specializes for more forms and reduces some overhead.

2

A similar optimization already existed since Python 3.10. 3.11 specializes for more forms. Furthermore, all attribute loads should be sped up by bpo-45947.

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.)

  • 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.)

FAQ

Q: How should I write my code to utilize these speedups?

A: You don’t have to change your code. Write Pythonic code that follows common best practices. The Faster CPython project optimizes for common code patterns we observe.


Q: Will CPython 3.11 use more memory?

A: Maybe not. We don’t expect memory use to exceed 20% more than 3.10. This is offset by memory optimizations for frame objects and object dictionaries as mentioned above.


Q: I don’t see any speedups in my workload. Why?

A: Certain code won’t have noticeable benefits. If your code spends most of its time on I/O operations, or already does most of its computation in a C extension library like numpy, there won’t be significant speedup. This project currently benefits pure-Python workloads the most.

Furthermore, the pyperformance figures are a geometric mean. Even within the pyperformance benchmarks, certain benchmarks have slowed down slightly, while others have sped up by nearly 2x!


Q: Is there a JIT compiler?

A: No. We’re still exploring other optimizations.

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.

CPython bytecode changes

  • The bytecode now contains inline cache entries, which take the form of CACHE instructions. Many opcodes expect to be followed by an exact number of caches, and instruct the interpreter to skip over them at runtime. Populated caches can look like arbitrary instructions, so great care should be taken when reading or modifying raw, adaptive bytecode containing quickened data.

  • Replaced all numeric BINARY_* and INPLACE_* instructions with a single BINARY_OP implementation.

  • Replaced the three call instructions: CALL_FUNCTION, CALL_FUNCTION_KW and CALL_METHOD with PUSH_NULL, PRECALL, CALL, and KW_NAMES. This decouples the argument shifting for methods from the handling of keyword arguments and allows better specialization of calls.

  • Removed COPY_DICT_WITHOUT_KEYS and GEN_START.

  • MATCH_CLASS and MATCH_KEYS no longer push an additional boolean value indicating whether the match succeeded or failed. Instead, they indicate failure with None (where a tuple of extracted values would otherwise be).

  • Replace several stack manipulation instructions (DUP_TOP, DUP_TOP_TWO, ROT_TWO, ROT_THREE, ROT_FOUR, and ROT_N) with new COPY and SWAP instructions.

  • Replaced JUMP_IF_NOT_EXC_MATCH by CHECK_EXC_MATCH which performs the check but does not jump.

  • Replaced JUMP_IF_NOT_EG_MATCH by CHECK_EG_MATCH which performs the check but does not jump.

  • Replaced JUMP_ABSOLUTE by the relative JUMP_BACKWARD.

  • Added JUMP_BACKWARD_NO_INTERRUPT, which is used in certain loops where it is undesirable to handle interrupts.

  • Replaced POP_JUMP_IF_TRUE and POP_JUMP_IF_FALSE by the relative POP_JUMP_FORWARD_IF_TRUE, POP_JUMP_BACKWARD_IF_TRUE, POP_JUMP_FORWARD_IF_FALSE and POP_JUMP_BACKWARD_IF_FALSE.

  • Added POP_JUMP_FORWARD_IF_NOT_NONE, POP_JUMP_BACKWARD_IF_NOT_NONE, POP_JUMP_FORWARD_IF_NONE and POP_JUMP_BACKWARD_IF_NONE opcodes to speed up conditional jumps.

  • JUMP_IF_TRUE_OR_POP and JUMP_IF_FALSE_OR_POP are now relative rather than absolute.

  • RESUME has been added. It is a no-op. Performs internal tracing, debugging and optimization checks.

Deprecated

  • 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 gh-89519.)

  • Octal escapes in string and bytes literals with value larger than 0o377 now produce DeprecationWarning. In a future Python version they will be a SyntaxWarning and eventually a SyntaxError. (Contributed by Serhiy Storchaka in gh-81548.)

  • The lib2to3 package and 2to3 tool are 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.)

  • Undocumented modules sre_compile, sre_constants and sre_parse are now deprecated. (Contributed by Serhiy Storchaka in bpo-47152.)

  • webbrowser.MacOSX is deprecated and will be removed in Python 3.13. It is untested and undocumented and also not used by webbrowser itself. (Contributed by Dong-hee Na in bpo-42255.)

  • The behavior of returning a value from a TestCase and IsolatedAsyncioTestCase test methods (other than the default None value), is now deprecated.

  • Deprecated the following unittest functions, scheduled for removal in Python 3.13:

    • unittest.findTestCases()

    • unittest.makeSuite()

    • unittest.getTestCaseNames()

    Use TestLoader method instead:

    (Contributed by Erlend E. Aasland in bpo-5846.)

  • The turtle.RawTurtle.settiltangle() is deprecated since Python 3.1, it now emits a deprecation warning and will be removed in Python 3.13. Use turtle.RawTurtle.tiltangle() instead (it was earlier incorrectly marked as deprecated, its docstring is now corrected). (Contributed by Hugo van Kemenade in bpo-45837.)

  • The delegation of int() to __trunc__() is now deprecated. Calling int(a) when type(a) implements __trunc__() but not __int__() or __index__() now raises a DeprecationWarning. (Contributed by Zackery Spytz in bpo-44977.)

  • The following have been deprecated in configparser since Python 3.2. Their deprecation warnings have now been updated to note they will removed in Python 3.12:

    • the configparser.SafeConfigParser class

    • the configparser.ParsingError.filename property

    • the configparser.RawConfigParser.readfp() method

    (Contributed by Hugo van Kemenade in bpo-45173.)

  • configparser.LegacyInterpolation has been deprecated in the docstring since Python 3.2. It now emits a DeprecationWarning and will be removed in Python 3.13. Use configparser.BasicInterpolation or configparser.ExtendedInterpolation instead. (Contributed by Hugo van Kemenade in bpo-46607.)

  • The locale.getdefaultlocale() function is deprecated and will be removed in Python 3.13. Use locale.setlocale(), locale.getpreferredencoding(False) and locale.getlocale() functions instead. (Contributed by Victor Stinner in gh-90817.)

  • The locale.resetlocale() function is deprecated and will be removed in Python 3.13. Use locale.setlocale(locale.LC_ALL, "") instead. (Contributed by Victor Stinner in gh-90817.)

  • The asynchat, asyncore and smtpd modules have been deprecated since at least Python 3.6. Their documentation and deprecation warnings have now been updated to note they will removed in Python 3.12 (PEP 594). (Contributed by Hugo van Kemenade in bpo-47022.)

  • PEP 594 led to the deprecations of the following modules which are slated for removal in Python 3.13:

    (Contributed by Brett Cannon in bpo-47061 and Victor Stinner in gh-68966.)

  • More strict rules will be applied now applied for numerical group references and group names in regular expressions in future Python versions. Only sequence of ASCII digits will be now accepted as a numerical reference. The group name in bytes patterns and replacement strings could only contain ASCII letters and digits and underscore. For now, a deprecation warning is raised for such syntax. (Contributed by Serhiy Storchaka in gh-91760.)

  • typing.Text, which exists solely to provide compatibility support between Python 2 and Python 3 code, is now deprecated. Its removal is currently unplanned, but users are encouraged to use str instead wherever possible. (Contributed by Alex Waygood in gh-92332.)

  • The keyword argument syntax for constructing TypedDict types is now deprecated. Support will be removed in Python 3.13. (Contributed by Jingchen Ye in gh-90224.)

  • The re.template() function and the corresponding re.TEMPLATE and re.T flags are deprecated, as they were undocumented and lacked an obvious purpose. They will be removed in Python 3.13. (Contributed by Serhiy Storchaka and Miro Hrončok in gh-92728.)

Pending Removal in Python 3.12

The following APIs have been deprecated in earlier Python releases, and will be removed in Python 3.12.

Python API:

C API:

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.)

  • The distutils bdist_msi command, deprecated in Python 3.9, is now removed. Use bdist_wheel (wheel packages) instead. (Contributed by Hugo van Kemenade in bpo-45124.)

  • Due to significant security concerns, the reuse_address parameter of asyncio.loop.create_datagram_endpoint(), disabled in Python 3.9, is now entirely removed. This is because of the behavior of the socket option SO_REUSEADDR in UDP. (Contributed by Hugo van Kemenade in bpo-45129.)

  • Removed __getitem__() methods of xml.dom.pulldom.DOMEventStream, wsgiref.util.FileWrapper and fileinput.FileInput, deprecated since Python 3.9. (Contributed by Hugo van Kemenade in bpo-45132.)

  • The following deprecated functions and methods are removed in the gettext module: lgettext(), ldgettext(), lngettext() and ldngettext().

    Function bind_textdomain_codeset(), methods output_charset() and set_output_charset(), and the codeset parameter of functions translation() and install() are also removed, since they are only used for the l*gettext() functions. (Contributed by Dong-hee Na and Serhiy Storchaka in bpo-44235.)

  • 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.)

  • Removed the deprecated split() method of _tkinter.TkappType. (Contributed by Erlend E. Aasland in bpo-38371.)

  • Removed from the inspect module:

    (Contributed by Hugo van Kemenade in bpo-45320.)

  • Remove namespace package support from unittest discovery. It was introduced in Python 3.4 but has been broken since Python 3.7. (Contributed by Inada Naoki in bpo-23882.)

  • Remove __class_getitem__ method from pathlib.PurePath, because it was not used and added by mistake in previous versions. (Contributed by Nikita Sobolev in bpo-46483.)

  • Remove the undocumented private float.__set_format__() method, previously known as float.__setformat__() in Python 3.7. Its docstring said: “You probably don’t want to use this function. It exists mainly to be used in Python’s test suite.” (Contributed by Victor Stinner in bpo-46852.)

  • The --experimental-isolated-subinterpreters configure flag (and corresponding EXPERIMENTAL_ISOLATED_SUBINTERPRETERS) have been removed.

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

  • Prohibited passing non-concurrent.futures.ThreadPoolExecutor executors to loop.set_default_executor() following a deprecation in Python 3.8. (Contributed by Illia Volochii in bpo-43234.)

  • open(), io.open(), codecs.open() and fileinput.FileInput no longer accept 'U' (“universal newline”) in the file mode. This flag was deprecated since Python 3.3. In Python 3, the “universal newline” is used by default when a file is open in text mode. The newline parameter of open() controls how universal newlines works. (Contributed by Victor Stinner in bpo-37330.)

  • The pdb module now reads the .pdbrc configuration file with the 'utf-8' encoding. (Contributed by Srinivas Reddy Thatiparthy (శ్రీనివాస్ రెడ్డి తాటిపర్తి) in bpo-41137.)

  • calendar: The calendar.LocaleTextCalendar and calendar.LocaleHTMLCalendar classes now use locale.getlocale(), instead of using locale.getdefaultlocale(), if no locale is specified. (Contributed by Victor Stinner in bpo-46659.)

  • Global inline flags (e.g. (?i)) can now only be used at the start of the regular expressions. Using them not at the start of expression was deprecated since Python 3.6. (Contributed by Serhiy Storchaka in bpo-47066.)

  • re module: Fix a few long-standing bugs where, in rare cases, capturing group could get wrong result. So the result may be different than before. (Contributed by Ma Lin in bpo-35859.)

  • The population parameter of random.sample() must be a sequence. Automatic conversion of sets to lists is no longer supported. If the sample size is larger than the population size, a ValueError is raised. (Contributed by Raymond Hettinger in bpo-40465.)

  • ast.AST node positions are now validated when provided to compile() and other related functions. If invalid positions are detected, a ValueError will be raised. (Contributed by Pablo Galindo in gh-93351)

  • tp_dictoffset should be treated as write-only. It can be set to describe C extension clases to the VM, but should be regarded as meaningless when read. To get the pointer to the object’s dictionary call PyObject_GenericGetDict() instead.

Build Changes

  • Building Python now requires a C11 compiler. Optional C11 features are not required. (Contributed by Victor Stinner in bpo-46656.)

  • Building Python now requires support of IEEE 754 floating point numbers. (Contributed by Victor Stinner in bpo-46917.)

  • CPython can now be built with the ThinLTO option via --with-lto=thin. (Contributed by Dong-hee Na and Brett Holman in bpo-44340.)

  • libpython is no longer linked against libcrypt. (Contributed by Mike Gilbert in bpo-45433.)

  • Building Python now requires a C99 <math.h> header file providing the following functions: copysign(), hypot(), isfinite(), isinf(), isnan(), round(). (Contributed by Victor Stinner in bpo-45440.)

  • Building Python now requires a C99 <math.h> header file providing a NAN constant, or the __builtin_nan() built-in function. (Contributed by Victor Stinner in bpo-46640.)

  • Building Python now requires support for floating point Not-a-Number (NaN): remove the Py_NO_NAN macro. (Contributed by Victor Stinner in bpo-46656.)

  • Freelists for object structs can now be disabled. A new configure option --without-freelists can be used to disable all freelists except empty tuple singleton. (Contributed by Christian Heimes in bpo-45522.)

  • Modules/Setup and Modules/makesetup have been improved and tied up. Extension modules can now be built through makesetup. All except some test modules can be linked statically into main binary or library. (Contributed by Brett Cannon and Christian Heimes in bpo-45548, bpo-45570, bpo-45571, and bpo-43974.)

  • Build dependencies, compiler flags, and linker flags for most stdlib extension modules are now detected by configure. libffi, libnsl, libsqlite3, zlib, bzip2, liblzma, libcrypt, Tcl/Tk, and uuid flags are detected by pkg-config (when available). tkinter now requires pkg-config command to detect development settings for Tcl/Tk headers and libraries. (Contributed by Christian Heimes and Erlend Egeberg Aasland in bpo-45847, bpo-45747, and bpo-45763.)

    Note

    Use the environment variables TCLTK_CFLAGS and TCLTK_LIBS to manually specify the location of Tcl/Tk headers and libraries. The configure options --with-tcltk-includes and --with-tcltk-libs have been removed.

    On RHEL 7 and CentOS 7 the development packages do not provide tcl.pc and tk.pc, use TCLTK_LIBS="-ltk8.5 -ltkstub8.5 -ltcl8.5". The directory Misc/rhel7 contains .pc files and instructions how to build Python with RHEL 7’s and CentOS 7’s Tcl/Tk and OpenSSL.

  • CPython now has PEP 11 tier 3 support for cross compiling to WebAssembly platform wasm32-unknown-emscripten (Python in the browser). The effort is inspired by previous work like Pyodide. Emscripten provides a limited subset of POSIX APIs. Python standard libraries features and modules related to networking, processes, threading, signals, mmap, and users/groups are not available or don’t work. (Contributed by Christian Heimes and Ethan Smith in gh-84461, promoted in gh-95085)

  • CPython now has PEP 11 tier 3 support for cross compiling to WebAssembly platform wasm32-unknown-wasi (WebAssembly System Interface). Like on Emscripten, only a subset of Python’s standard library is available on WASI. (Contributed by Christian Heimes in gh-90473, promoted in gh-95085)

  • CPython will now use 30-bit digits by default for the Python int implementation. Previously, the default was to use 30-bit digits on platforms with SIZEOF_VOID_P >= 8, and 15-bit digits otherwise. It’s still possible to explicitly request use of 15-bit digits via either the --enable-big-digits option to the configure script or (for Windows) the PYLONG_BITS_IN_DIGIT variable in PC/pyconfig.h, but this option may be removed at some point in the future. (Contributed by Mark Dickinson in bpo-45569.)

  • The tkinter package now requires Tcl/Tk version 8.5.12 or newer. (Contributed by Serhiy Storchaka in bpo-46996.)

C API Changes

New Features

Porting to Python 3.11

  • PyErr_SetExcInfo() no longer uses the type and traceback arguments, the interpreter now derives those values from the exception instance (the value argument). The function still steals references of all three arguments. (Contributed by Irit Katriel in bpo-45711.)

  • PyErr_GetExcInfo() now derives the type and traceback fields of the result from the exception instance (the value field). (Contributed by Irit Katriel in bpo-45711.)

  • _frozen has a new is_package field to indicate whether or not the frozen module is a package. Previously, a negative value in the size field was the indicator. Now only non-negative values be used for size. (Contributed by Kumar Aditya in bpo-46608.)

  • _PyFrameEvalFunction() now takes _PyInterpreterFrame* as its second parameter, instead of PyFrameObject*. See PEP 523 for more details of how to use this function pointer type.

  • PyCode_New() and PyCode_NewWithPosOnlyArgs() now take an additional exception_table argument. Using these functions should be avoided, if at all possible. To get a custom code object: create a code object using the compiler, then get a modified version with the replace method.

  • PyCodeObject no longer has the co_code, co_varnames, co_cellvars and co_freevars fields. Instead, use PyCode_GetCode(), PyCode_GetVarnames(), PyCode_GetCellvars() and PyCode_GetFreevars() respectively to access them via the C API. (Contributed by Brandt Bucher in bpo-46841 and Ken Jin in gh-92154 and gh-94936.)

  • 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)

  • Since Py_TYPE() is changed to a inline static function, Py_TYPE(obj) = new_type must be replaced with Py_SET_TYPE(obj, new_type): see the Py_SET_TYPE() function (available since Python 3.9). For backward compatibility, this macro can be used:

    #if PY_VERSION_HEX < 0x030900A4 && !defined(Py_SET_TYPE)
    static inline void _Py_SET_TYPE(PyObject *ob, PyTypeObject *type)
    { ob->ob_type = type; }
    #define Py_SET_TYPE(ob, type) _Py_SET_TYPE((PyObject*)(ob), type)
    #endif
    

    (Contributed by Victor Stinner in bpo-39573.)

  • Since Py_SIZE() is changed to a inline static function, Py_SIZE(obj) = new_size must be replaced with Py_SET_SIZE(obj, new_size): see the Py_SET_SIZE() function (available since Python 3.9). For backward compatibility, this macro can be used:

    #if PY_VERSION_HEX < 0x030900A4 && !defined(Py_SET_SIZE)
    static inline void _Py_SET_SIZE(PyVarObject *ob, Py_ssize_t size)
    { ob->ob_size = size; }
    #define Py_SET_SIZE(ob, size) _Py_SET_SIZE((PyVarObject*)(ob), size)
    #endif
    

    (Contributed by Victor Stinner in bpo-39573.)

  • <Python.h> no longer includes the header files <stdlib.h>, <stdio.h>, <errno.h> and <string.h> when the Py_LIMITED_API macro is set to 0x030b0000 (Python 3.11) or higher. C extensions should explicitly include the header files after #include <Python.h>. (Contributed by Victor Stinner in bpo-45434.)

  • The non-limited API files cellobject.h, classobject.h, code.h, context.h, funcobject.h, genobject.h and longintrepr.h have been moved to the Include/cpython directory. Moreover, the eval.h header file was removed. These files must not be included directly, as they are already included in Python.h: Include Files. If they have been included directly, consider including Python.h instead. (Contributed by Victor Stinner in bpo-35134.)

  • The PyUnicode_CHECK_INTERNED() macro has been excluded from the limited C API. It was never usable there, because it used internal structures which are not available in the limited C API. (Contributed by Victor Stinner in bpo-46007.)

  • The following frame functions and type are now directly available with #include <Python.h>, it’s no longer needed to add #include <frameobject.h>:

    (Contributed by Victor Stinner in gh-93937.)

  • The PyFrameObject structure members have been removed from the public C API.

    While the documentation notes that the PyFrameObject fields are subject to change at any time, they have been stable for a long time and were used in several popular extensions.

    In Python 3.11, the frame struct was reorganized to allow performance optimizations. Some fields were removed entirely, as they were details of the old implementation.

    PyFrameObject fields:

    The Python frame object is now created lazily. A side effect is that the f_back member must not be accessed directly, since its value is now also computed lazily. The PyFrame_GetBack() function must be called instead.

    Debuggers that accessed the f_locals directly must call PyFrame_GetLocals() instead. They no longer need to call PyFrame_FastToLocalsWithError() or PyFrame_LocalsToFast(), in fact they should not call those functions. The necessary updating of the frame is now managed by the virtual machine.

    Code defining PyFrame_GetCode() on Python 3.8 and older:

    #if PY_VERSION_HEX < 0x030900B1
    static inline PyCodeObject* PyFrame_GetCode(PyFrameObject *frame)
    {
        Py_INCREF(frame->f_code);
        return frame->f_code;
    }
    #endif
    

    Code defining PyFrame_GetBack() on Python 3.8 and older:

    #if PY_VERSION_HEX < 0x030900B1
    static inline PyFrameObject* PyFrame_GetBack(PyFrameObject *frame)
    {
        Py_XINCREF(frame->f_back);
        return frame->f_back;
    }
    #endif
    

    Or use the pythoncapi_compat project to get these two functions on older Python versions.

  • Changes of the PyThreadState structure members:

    Code defining PyThreadState_GetFrame() on Python 3.8 and older:

    #if PY_VERSION_HEX < 0x030900B1
    static inline PyFrameObject* PyThreadState_GetFrame(PyThreadState *tstate)
    {
        Py_XINCREF(tstate->frame);
        return tstate->frame;
    }
    #endif
    

    Code defining PyThreadState_EnterTracing() and PyThreadState_LeaveTracing() on Python 3.10 and older:

    #if PY_VERSION_HEX < 0x030B00A2
    static inline void PyThreadState_EnterTracing(PyThreadState *tstate)
    {
        tstate->tracing++;
    #if PY_VERSION_HEX >= 0x030A00A1
        tstate->cframe->use_tracing = 0;
    #else
        tstate->use_tracing = 0;
    #endif
    }
    
    static inline void PyThreadState_LeaveTracing(PyThreadState *tstate)
    {
        int use_tracing = (tstate->c_tracefunc != NULL || tstate->c_profilefunc != NULL);
        tstate->tracing--;
    #if PY_VERSION_HEX >= 0x030A00A1
        tstate->cframe->use_tracing = use_tracing;
    #else
        tstate->use_tracing = use_tracing;
    #endif
    }
    #endif
    

    Or use the pythoncapi_compat project to get these functions on old Python functions.

  • Distributors are encouraged to build Python with the optimized Blake2 library libb2.

  • The PyConfig.module_search_paths_set field must now be set to 1 for initialization to use PyConfig.module_search_paths to initialize sys.path. Otherwise, initialization will recalculate the path and replace any values added to module_search_paths.

  • PyConfig_Read() no longer calculates the initial search path, and will not fill any values into PyConfig.module_search_paths. To calculate default paths and then modify them, finish initialization and use PySys_GetObject() to retrieve sys.path as a Python list object and modify it directly.

Deprecated

Removed

  • PyFrame_BlockSetup() and PyFrame_BlockPop() have been removed. (Contributed by Mark Shannon in bpo-40222.)

  • Remove the following math macros using the errno variable:

    • Py_ADJUST_ERANGE1()

    • Py_ADJUST_ERANGE2()

    • Py_OVERFLOWED()

    • Py_SET_ERANGE_IF_OVERFLOW()

    • Py_SET_ERRNO_ON_MATH_ERROR()

    (Contributed by Victor Stinner in bpo-45412.)

  • Remove Py_UNICODE_COPY() and Py_UNICODE_FILL() macros, deprecated since Python 3.3. Use PyUnicode_CopyCharacters() or memcpy() (wchar_t* string), and PyUnicode_Fill() functions instead. (Contributed by Victor Stinner in bpo-41123.)

  • Remove the pystrhex.h header file. It only contains private functions. C extensions should only include the main <Python.h> header file. (Contributed by Victor Stinner in bpo-45434.)

  • Remove the Py_FORCE_DOUBLE() macro. It was used by the Py_IS_INFINITY() macro. (Contributed by Victor Stinner in bpo-45440.)

  • The following items are no longer available when Py_LIMITED_API is defined:

    These are not part of the limited API.

    (Contributed by Victor Stinner in bpo-45474.)

  • Exclude PyWeakref_GET_OBJECT() from the limited C API. It never worked since the PyWeakReference structure is opaque in the limited C API. (Contributed by Victor Stinner in bpo-35134.)

  • Remove the PyHeapType_GET_MEMBERS() macro. It was exposed in the public C API by mistake, it must only be used by Python internally. Use the PyTypeObject.tp_members member instead. (Contributed by Victor Stinner in bpo-40170.)

  • Remove the HAVE_PY_SET_53BIT_PRECISION macro (moved to the internal C API). (Contributed by Victor Stinner in bpo-45412.)

  • Remove the Py_UNICODE encoder APIs, as they have been deprecated since Python 3.3, are little used and are inefficient relative to the recommended alternatives.

    The removed functions are:

    • PyUnicode_Encode()

    • PyUnicode_EncodeASCII()

    • PyUnicode_EncodeLatin1()

    • PyUnicode_EncodeUTF7()

    • PyUnicode_EncodeUTF8()

    • PyUnicode_EncodeUTF16()

    • PyUnicode_EncodeUTF32()

    • PyUnicode_EncodeUnicodeEscape()

    • PyUnicode_EncodeRawUnicodeEscape()

    • PyUnicode_EncodeCharmap()

    • PyUnicode_TranslateCharmap()

    • PyUnicode_EncodeDecimal()

    • PyUnicode_TransformDecimalToASCII()

    See PEP 624 for details and migration guidance. (Contributed by Inada Naoki in bpo-44029.)