Is python 3.9 the latest?

Dictionary Merge & Update Operators¶

Merge [|] and update [|=] operators have been added to the built-in dict class. Those complement the existing dict.update and {**d1, **d2} methods of merging dictionaries.

Example:

>>> x = {"key1": "value1 from x", "key2": "value2 from x"}
>>> y = {"key2": "value2 from y", "key3": "value3 from y"}
>>> x | y
{'key1': 'value1 from x', 'key2': 'value2 from y', 'key3': 'value3 from y'}
>>> y | x
{'key2': 'value2 from x', 'key3': 'value3 from y', 'key1': 'value1 from x'}

See PEP 584 for a full description. [Contributed by Brandt Bucher in bpo-36144.]

New String Methods to Remove Prefixes and Suffixes¶

str.removeprefix[prefix] and str.removesuffix[suffix] have been added to easily remove an unneeded prefix or a suffix from a string. Corresponding bytes, bytearray, and collections.UserString methods have also been added. See PEP 616 for a full description. [Contributed by Dennis Sweeney in bpo-39939.]

Type Hinting Generics in Standard Collections¶

In type annotations you can now use built-in collection types such as list and dict as generic types instead of importing the corresponding capitalized types [e.g. List or Dict] from typing. Some other types in the standard library are also now generic, for example queue.Queue.

Example:

def greet_all[names: list[str]] -> None:
    for name in names:
        print["Hello", name]

See PEP 585 for more details. [Contributed by Guido van Rossum, Ethan Smith, and Batuhan Taşkaya in bpo-39481.]

New Parser¶

Python 3.9 uses a new parser, based on PEG instead of LL[1]. The new parser’s performance is roughly comparable to that of the old parser, but the PEG formalism is more flexible than LL[1] when it comes to designing new language features. We’ll start using this flexibility in Python 3.10 and later.

The ast module uses the new parser and produces the same AST as the old parser.

In Python 3.10, the old parser will be deleted and so will all functionality that depends on it [primarily the parser module, which has long been deprecated]. In Python 3.9 only, you can switch back to the LL[1] parser using a command line switch [-X oldparser] or an environment variable [PYTHONOLDPARSER=1].

See PEP 617 for more details. [Contributed by Guido van Rossum, Pablo Galindo and Lysandros Nikolaou in bpo-40334.]

zoneinfo¶

The zoneinfo module brings support for the IANA time zone database to the standard library. It adds zoneinfo.ZoneInfo, a concrete datetime.tzinfo implementation backed by the system’s time zone data.

Example:

>>> from zoneinfo import ZoneInfo
>>> from datetime import datetime, timedelta

>>> # Daylight saving time
>>> dt = datetime[2020, 10, 31, 12, tzinfo=ZoneInfo["America/Los_Angeles"]]
>>> print[dt]
2020-10-31 12:00:00-07:00
>>> dt.tzname[]
'PDT'

>>> # Standard time
>>> dt += timedelta[days=7]
>>> print[dt]
2020-11-07 12:00:00-08:00
>>> print[dt.tzname[]]
PST

As a fall-back source of data for platforms that don’t ship the IANA database, the tzdata module was released as a first-party package – distributed via PyPI and maintained by the CPython core team.

See also

PEP written and implemented by Paul Ganssle

graphlib¶

A new module, graphlib, was added that contains the graphlib.TopologicalSorter class to offer functionality to perform topological sorting of graphs. [Contributed by Pablo Galindo, Tim Peters and Larry Hastings in bpo-17005.]

ast¶

Added the indent option to dump[] which allows it to produce a multiline indented output. [Contributed by Serhiy Storchaka in bpo-37995.]

Added ast.unparse[] as a function in the ast module that can be used to unparse an ast.AST object and produce a string with code that would produce an equivalent ast.AST object when parsed. [Contributed by Pablo Galindo and Batuhan Taskaya in bpo-38870.]

Added docstrings to AST nodes that contains the ASDL signature used to construct that node. [Contributed by Batuhan Taskaya in bpo-39638.]

asyncio¶

Due to significant security concerns, the reuse_address parameter of asyncio.loop.create_datagram_endpoint[] is no longer supported. This is because of the behavior of the socket option SO_REUSEADDR in UDP. For more details, see the documentation for loop.create_datagram_endpoint[]. [Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in bpo-37228.]

Added a new coroutine shutdown_default_executor[] that schedules a shutdown for the default executor that waits on the ThreadPoolExecutor to finish closing. Also, asyncio.run[] has been updated to use the new coroutine. [Contributed by Kyle Stanley in bpo-34037.]

Added asyncio.PidfdChildWatcher, a Linux-specific child watcher implementation that polls process file descriptors. [bpo-38692]

Added a new coroutine asyncio.to_thread[]. It is mainly used for running IO-bound functions in a separate thread to avoid blocking the event loop, and essentially works as a high-level version of run_in_executor[] that can directly take keyword arguments. [Contributed by Kyle Stanley and Yury Selivanov in bpo-32309.]

When cancelling the task due to a timeout, asyncio.wait_for[] will now wait until the cancellation is complete also in the case when timeout is = 0x03090000 // This was not needed before Python 3.9 [Python issue 35810 and 40217] Py_VISIT[Py_TYPE[self]]; #endif }

If your traverse function delegates to tp_traverse of its base class [or another type], ensure that Py_TYPE[self] is visited only once. Note that only heap type are expected to visit the type in tp_traverse.

For example, if your tp_traverse function includes:

base->tp_traverse[self, visit, arg]

then add:

#if PY_VERSION_HEX >= 0x03090000
    // This was not needed before Python 3.9 [bpo-35810 and bpo-40217]
    if [base->tp_flags & Py_TPFLAGS_HEAPTYPE] {
        // a heap type's tp_traverse already visited Py_TYPE[self]
    } else {
        Py_VISIT[Py_TYPE[self]];
    }
#else

[See bpo-35810 and bpo-40217 for more information.]

CPython bytecode changes¶

• The LOAD_ASSERTION_ERROR opcode was added for handling the assert statement. Previously, the assert statement would not work correctly if the AssertionError exception was being shadowed. [Contributed by Zackery Spytz in bpo-34880.]

• The COMPARE_OP opcode was split into four distinct instructions:

  • COMPARE_OP for rich comparisons

  • IS_OP for ‘is’ and ‘is not’ tests

  • CONTAINS_OP for ‘in’ and ‘not in’ tests

  • JUMP_IF_NOT_EXC_MATCH for checking exceptions in ‘try-except’ statements.

  [Contributed by Mark Shannon in bpo-39156.]

New Features¶

• PEP 573: Added PyType_FromModuleAndSpec[] to associate a module with a class; PyType_GetModule[] and PyType_GetModuleState[] to retrieve the module and its state; and PyCMethod and METH_METHOD to allow a method to access the class it was defined in. [Contributed by Marcel Plch and Petr Viktorin in bpo-38787.]

• Added PyFrame_GetCode[] function: get a frame code. Added PyFrame_GetBack[] function: get the frame next outer frame. [Contributed by Victor Stinner in bpo-40421.]

• Added PyFrame_GetLineNumber[] to the limited C API. [Contributed by Victor Stinner in bpo-40421.]

• Added PyThreadState_GetInterpreter[] and PyInterpreterState_Get[] functions to get the interpreter. Added PyThreadState_GetFrame[] function to get the current frame of a Python thread state. Added PyThreadState_GetID[] function: get the unique identifier of a Python thread state. [Contributed by Victor Stinner in bpo-39947.]

• Added a new public PyObject_CallNoArgs[] function to the C API, which calls a callable Python object without any arguments. It is the most efficient way to call a callable Python object without any argument. [Contributed by Victor Stinner in bpo-37194.]

• Changes in the limited C API [if Py_LIMITED_API macro is defined]:

  • Provide Py_EnterRecursiveCall[] and Py_LeaveRecursiveCall[] as regular functions for the limited API. Previously, there were defined as macros, but these macros didn’t compile with the limited C API which cannot access PyThreadState.recursion_depth field [the structure is opaque in the limited C API].

  • PyObject_INIT[] and PyObject_INIT_VAR[] become regular “opaque” function to hide implementation details.

  [Contributed by Victor Stinner in bpo-38644 and bpo-39542.]

• The PyModule_AddType[] function is added to help adding a type to a module. [Contributed by Dong-hee Na in bpo-40024.]

• Added the functions PyObject_GC_IsTracked[] and PyObject_GC_IsFinalized[] to the public API to allow to query if Python objects are being currently tracked or have been already finalized by the garbage collector respectively. [Contributed by Pablo Galindo Salgado in bpo-40241.]

• Added _PyObject_FunctionStr[] to get a user-friendly string representation of a function-like object. [Patch by Jeroen Demeyer in bpo-37645.]

• Added PyObject_CallOneArg[] for calling an object with one positional argument [Patch by Jeroen Demeyer in bpo-37483.]

Porting to Python 3.9¶

• PyInterpreterState.eval_frame [PEP 523] now requires a new mandatory tstate parameter [PyThreadState*]. [Contributed by Victor Stinner in bpo-38500.]

• Extension modules: m_traverse, m_clear and m_free functions of PyModuleDef are no longer called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed [Py_mod_exec function]. More precisely, these functions are not called if m_size is greater than 0 and the module state [as returned by PyModule_GetState[]] is NULL.

  Extension modules without module state [m_size >> from typing import Literal >>> Literal[{0}] >>> Literal[{0}] == Literal[{False}] Traceback [most recent call last]: File "", line 1, in TypeError: unhashable type: 'set'

[Contributed by Yurii Karabas in bpo-42345.]

macOS 11.0 [Big Sur] and Apple Silicon Mac support¶

As of 3.9.1, Python now fully supports building and running on macOS 11.0 [Big Sur] and on Apple Silicon Macs [based on the ARM64 architecture]. A new universal build variant, universal2, is now available to natively support both ARM64 and Intel 64 in one set of executables. Binaries can also now be built on current versions of macOS to be deployed on a range of older macOS versions [tested to 10.9] while making some newer OS functions and options conditionally available based on the operating system version in use at runtime [“weaklinking”].

[Contributed by Ronald Oussoren and Lawrence D’Anna in bpo-41100.]

collections.abc¶

collections.abc.Callable generic now flattens type parameters, similar to what typing.Callable currently does. This means that collections.abc.Callable[[int, str], str] will have __args__ of [int, str, str]; previously this was [[int, str], str]. To allow this change, types.GenericAlias can now be subclassed, and a subclass will be returned when subscripting the collections.abc.Callable type. Code which accesses the arguments via typing.get_args[] or __args__ need to account for this change. A DeprecationWarning may be emitted for invalid forms of parameterizing collections.abc.Callable which may have passed silently in Python 3.9.1. This DeprecationWarning will become a TypeError in Python 3.10. [Contributed by Ken Jin in bpo-42195.]

urllib.parse¶

Earlier Python versions allowed using both ; and & as query parameter separators in urllib.parse.parse_qs[] and urllib.parse.parse_qsl[]. Due to security concerns, and to conform with newer W3C recommendations, this has been changed to allow only a single separator key, with & as the default. This change also affects cgi.parse[] and cgi.parse_multipart[] as they use the affected functions internally. For more details, please see their respective documentation. [Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in bpo-42967.]