1**************************** 2 What's New In Python 3.8 3**************************** 4 5.. Rules for maintenance: 6 7 * Anyone can add text to this document. Do not spend very much time 8 on the wording of your changes, because your text will probably 9 get rewritten to some degree. 10 11 * The maintainer will go through Misc/NEWS periodically and add 12 changes; it's therefore more important to add your changes to 13 Misc/NEWS than to this file. 14 15 * This is not a complete list of every single change; completeness 16 is the purpose of Misc/NEWS. Some changes I consider too small 17 or esoteric to include. If such a change is added to the text, 18 I'll just remove it. (This is another reason you shouldn't spend 19 too much time on writing your addition.) 20 21 * If you want to draw your new text to the attention of the 22 maintainer, add 'XXX' to the beginning of the paragraph or 23 section. 24 25 * It's OK to just add a fragmentary note about a change. For 26 example: "XXX Describe the transmogrify() function added to the 27 socket module." The maintainer will research the change and 28 write the necessary text. 29 30 * You can comment out your additions if you like, but it's not 31 necessary (especially when a final release is some months away). 32 33 * Credit the author of a patch or bugfix. Just the name is 34 sufficient; the e-mail address isn't necessary. 35 36 * It's helpful to add the bug/patch number as a comment: 37 38 XXX Describe the transmogrify() function added to the socket 39 module. 40 (Contributed by P.Y. Developer in :issue:`12345`.) 41 42 This saves the maintainer the effort of going through the Git log 43 when researching a change. 44 45:Editor: Raymond Hettinger 46 47This article explains the new features in Python 3.8, compared to 3.7. 48Python 3.8 was released on October 14, 2019. 49For full details, see the :ref:`changelog <changelog>`. 50 51.. testsetup:: 52 53 from datetime import date 54 from math import cos, radians 55 from unicodedata import normalize 56 import re 57 import math 58 59 60Summary -- Release highlights 61============================= 62 63.. This section singles out the most important changes in Python 3.8. 64 Brevity is key. 65 66 67.. PEP-sized items next. 68 69 70 71New Features 72============ 73 74Assignment expressions 75---------------------- 76 77There is new syntax ``:=`` that assigns values to variables as part of a larger 78expression. It is affectionately known as "the walrus operator" due to 79its resemblance to `the eyes and tusks of a walrus 80<https://en.wikipedia.org/wiki/Walrus#/media/File:Pacific_Walrus_-_Bull_(8247646168).jpg>`_. 81 82In this example, the assignment expression helps avoid calling 83:func:`len` twice:: 84 85 if (n := len(a)) > 10: 86 print(f"List is too long ({n} elements, expected <= 10)") 87 88A similar benefit arises during regular expression matching where 89match objects are needed twice, once to test whether a match 90occurred and another to extract a subgroup:: 91 92 discount = 0.0 93 if (mo := re.search(r'(\d+)% discount', advertisement)): 94 discount = float(mo.group(1)) / 100.0 95 96The operator is also useful with while-loops that compute 97a value to test loop termination and then need that same 98value again in the body of the loop:: 99 100 # Loop over fixed length blocks 101 while (block := f.read(256)) != '': 102 process(block) 103 104Another motivating use case arises in list comprehensions where 105a value computed in a filtering condition is also needed in 106the expression body:: 107 108 [clean_name.title() for name in names 109 if (clean_name := normalize('NFC', name)) in allowed_names] 110 111Try to limit use of the walrus operator to clean cases that reduce 112complexity and improve readability. 113 114See :pep:`572` for a full description. 115 116(Contributed by Emily Morehouse in :issue:`35224`.) 117 118 119Positional-only parameters 120-------------------------- 121 122There is a new function parameter syntax ``/`` to indicate that some 123function parameters must be specified positionally and cannot be used as 124keyword arguments. This is the same notation shown by ``help()`` for C 125functions annotated with Larry Hastings' 126:ref:`Argument Clinic <howto-clinic>` tool. 127 128In the following example, parameters *a* and *b* are positional-only, 129while *c* or *d* can be positional or keyword, and *e* or *f* are 130required to be keywords:: 131 132 def f(a, b, /, c, d, *, e, f): 133 print(a, b, c, d, e, f) 134 135The following is a valid call:: 136 137 f(10, 20, 30, d=40, e=50, f=60) 138 139However, these are invalid calls:: 140 141 f(10, b=20, c=30, d=40, e=50, f=60) # b cannot be a keyword argument 142 f(10, 20, 30, 40, 50, f=60) # e must be a keyword argument 143 144One use case for this notation is that it allows pure Python functions 145to fully emulate behaviors of existing C coded functions. For example, 146the built-in :func:`divmod` function does not accept keyword arguments:: 147 148 def divmod(a, b, /): 149 "Emulate the built in divmod() function" 150 return (a // b, a % b) 151 152Another use case is to preclude keyword arguments when the parameter 153name is not helpful. For example, the builtin :func:`len` function has 154the signature ``len(obj, /)``. This precludes awkward calls such as:: 155 156 len(obj='hello') # The "obj" keyword argument impairs readability 157 158A further benefit of marking a parameter as positional-only is that it 159allows the parameter name to be changed in the future without risk of 160breaking client code. For example, in the :mod:`statistics` module, the 161parameter name *dist* may be changed in the future. This was made 162possible with the following function specification:: 163 164 def quantiles(dist, /, *, n=4, method='exclusive') 165 ... 166 167Since the parameters to the left of ``/`` are not exposed as possible 168keywords, the parameters names remain available for use in ``**kwargs``:: 169 170 >>> def f(a, b, /, **kwargs): 171 ... print(a, b, kwargs) 172 ... 173 >>> f(10, 20, a=1, b=2, c=3) # a and b are used in two ways 174 10 20 {'a': 1, 'b': 2, 'c': 3} 175 176This greatly simplifies the implementation of functions and methods 177that need to accept arbitrary keyword arguments. For example, here 178is an excerpt from code in the :mod:`collections` module:: 179 180 class Counter(dict): 181 182 def __init__(self, iterable=None, /, **kwds): 183 # Note "iterable" is a possible keyword argument 184 185See :pep:`570` for a full description. 186 187(Contributed by Pablo Galindo in :issue:`36540`.) 188 189.. TODO: Pablo will sprint on docs at PyCon US 2019. 190 191 192Parallel filesystem cache for compiled bytecode files 193----------------------------------------------------- 194 195The new :envvar:`PYTHONPYCACHEPREFIX` setting (also available as 196:option:`-X` ``pycache_prefix``) configures the implicit bytecode 197cache to use a separate parallel filesystem tree, rather than 198the default ``__pycache__`` subdirectories within each source 199directory. 200 201The location of the cache is reported in :data:`sys.pycache_prefix` 202(:const:`None` indicates the default location in ``__pycache__`` 203subdirectories). 204 205(Contributed by Carl Meyer in :issue:`33499`.) 206 207 208Debug build uses the same ABI as release build 209----------------------------------------------- 210 211Python now uses the same ABI whether it's built in release or debug mode. On 212Unix, when Python is built in debug mode, it is now possible to load C 213extensions built in release mode and C extensions built using the stable ABI. 214 215Release builds and :ref:`debug builds <debug-build>` are now ABI compatible: defining the 216``Py_DEBUG`` macro no longer implies the ``Py_TRACE_REFS`` macro, which 217introduces the only ABI incompatibility. The ``Py_TRACE_REFS`` macro, which 218adds the :func:`sys.getobjects` function and the :envvar:`PYTHONDUMPREFS` 219environment variable, can be set using the new :option:`./configure 220--with-trace-refs <--with-trace-refs>` build option. 221(Contributed by Victor Stinner in :issue:`36465`.) 222 223On Unix, C extensions are no longer linked to libpython except on Android 224and Cygwin. 225It is now possible 226for a statically linked Python to load a C extension built using a shared 227library Python. 228(Contributed by Victor Stinner in :issue:`21536`.) 229 230On Unix, when Python is built in debug mode, import now also looks for C 231extensions compiled in release mode and for C extensions compiled with the 232stable ABI. 233(Contributed by Victor Stinner in :issue:`36722`.) 234 235To embed Python into an application, a new ``--embed`` option must be passed to 236``python3-config --libs --embed`` to get ``-lpython3.8`` (link the application 237to libpython). To support both 3.8 and older, try ``python3-config --libs 238--embed`` first and fallback to ``python3-config --libs`` (without ``--embed``) 239if the previous command fails. 240 241Add a pkg-config ``python-3.8-embed`` module to embed Python into an 242application: ``pkg-config python-3.8-embed --libs`` includes ``-lpython3.8``. 243To support both 3.8 and older, try ``pkg-config python-X.Y-embed --libs`` first 244and fallback to ``pkg-config python-X.Y --libs`` (without ``--embed``) if the 245previous command fails (replace ``X.Y`` with the Python version). 246 247On the other hand, ``pkg-config python3.8 --libs`` no longer contains 248``-lpython3.8``. C extensions must not be linked to libpython (except on 249Android and Cygwin, whose cases are handled by the script); 250this change is backward incompatible on purpose. 251(Contributed by Victor Stinner in :issue:`36721`.) 252 253.. _bpo-36817-whatsnew: 254 255f-strings support ``=`` for self-documenting expressions and debugging 256---------------------------------------------------------------------- 257 258Added an ``=`` specifier to :term:`f-string`\s. An f-string such as 259``f'{expr=}'`` will expand to the text of the expression, an equal sign, 260then the representation of the evaluated expression. For example: 261 262 >>> user = 'eric_idle' 263 >>> member_since = date(1975, 7, 31) 264 >>> f'{user=} {member_since=}' 265 "user='eric_idle' member_since=datetime.date(1975, 7, 31)" 266 267The usual :ref:`f-string format specifiers <f-strings>` allow more 268control over how the result of the expression is displayed:: 269 270 >>> delta = date.today() - member_since 271 >>> f'{user=!s} {delta.days=:,d}' 272 'user=eric_idle delta.days=16,075' 273 274The ``=`` specifier will display the whole expression so that 275calculations can be shown:: 276 277 >>> print(f'{theta=} {cos(radians(theta))=:.3f}') 278 theta=30 cos(radians(theta))=0.866 279 280(Contributed by Eric V. Smith and Larry Hastings in :issue:`36817`.) 281 282 283PEP 578: Python Runtime Audit Hooks 284----------------------------------- 285 286The PEP adds an Audit Hook and Verified Open Hook. Both are available from 287Python and native code, allowing applications and frameworks written in pure 288Python code to take advantage of extra notifications, while also allowing 289embedders or system administrators to deploy builds of Python where auditing is 290always enabled. 291 292See :pep:`578` for full details. 293 294 295PEP 587: Python Initialization Configuration 296-------------------------------------------- 297 298The :pep:`587` adds a new C API to configure the Python Initialization 299providing finer control on the whole configuration and better error reporting. 300 301New structures: 302 303* :c:type:`PyConfig` 304* :c:type:`PyPreConfig` 305* :c:type:`PyStatus` 306* :c:type:`PyWideStringList` 307 308New functions: 309 310* :c:func:`PyConfig_Clear` 311* :c:func:`PyConfig_InitIsolatedConfig` 312* :c:func:`PyConfig_InitPythonConfig` 313* :c:func:`PyConfig_Read` 314* :c:func:`PyConfig_SetArgv` 315* :c:func:`PyConfig_SetBytesArgv` 316* :c:func:`PyConfig_SetBytesString` 317* :c:func:`PyConfig_SetString` 318* :c:func:`PyPreConfig_InitIsolatedConfig` 319* :c:func:`PyPreConfig_InitPythonConfig` 320* :c:func:`PyStatus_Error` 321* :c:func:`PyStatus_Exception` 322* :c:func:`PyStatus_Exit` 323* :c:func:`PyStatus_IsError` 324* :c:func:`PyStatus_IsExit` 325* :c:func:`PyStatus_NoMemory` 326* :c:func:`PyStatus_Ok` 327* :c:func:`PyWideStringList_Append` 328* :c:func:`PyWideStringList_Insert` 329* :c:func:`Py_BytesMain` 330* :c:func:`Py_ExitStatusException` 331* :c:func:`Py_InitializeFromConfig` 332* :c:func:`Py_PreInitialize` 333* :c:func:`Py_PreInitializeFromArgs` 334* :c:func:`Py_PreInitializeFromBytesArgs` 335* :c:func:`Py_RunMain` 336 337This PEP also adds ``_PyRuntimeState.preconfig`` (:c:type:`PyPreConfig` type) 338and ``PyInterpreterState.config`` (:c:type:`PyConfig` type) fields to these 339internal structures. ``PyInterpreterState.config`` becomes the new 340reference configuration, replacing global configuration variables and 341other private variables. 342 343See :ref:`Python Initialization Configuration <init-config>` for the 344documentation. 345 346See :pep:`587` for a full description. 347 348(Contributed by Victor Stinner in :issue:`36763`.) 349 350 351PEP 590: Vectorcall: a fast calling protocol for CPython 352-------------------------------------------------------- 353 354:ref:`vectorcall` is added to the Python/C API. 355It is meant to formalize existing optimizations which were already done 356for various classes. 357Any :ref:`static type <static-types>` implementing a callable can use this 358protocol. 359 360This is currently provisional. 361The aim is to make it fully public in Python 3.9. 362 363See :pep:`590` for a full description. 364 365(Contributed by Jeroen Demeyer, Mark Shannon and Petr Viktorin in :issue:`36974`.) 366 367 368Pickle protocol 5 with out-of-band data buffers 369----------------------------------------------- 370 371When :mod:`pickle` is used to transfer large data between Python processes 372in order to take advantage of multi-core or multi-machine processing, 373it is important to optimize the transfer by reducing memory copies, and 374possibly by applying custom techniques such as data-dependent compression. 375 376The :mod:`pickle` protocol 5 introduces support for out-of-band buffers 377where :pep:`3118`-compatible data can be transmitted separately from the 378main pickle stream, at the discretion of the communication layer. 379 380See :pep:`574` for a full description. 381 382(Contributed by Antoine Pitrou in :issue:`36785`.) 383 384 385Other Language Changes 386====================== 387 388* A :keyword:`continue` statement was illegal in the :keyword:`finally` clause 389 due to a problem with the implementation. In Python 3.8 this restriction 390 was lifted. 391 (Contributed by Serhiy Storchaka in :issue:`32489`.) 392 393* The :class:`bool`, :class:`int`, and :class:`fractions.Fraction` types 394 now have an :meth:`~int.as_integer_ratio` method like that found in 395 :class:`float` and :class:`decimal.Decimal`. This minor API extension 396 makes it possible to write ``numerator, denominator = 397 x.as_integer_ratio()`` and have it work across multiple numeric types. 398 (Contributed by Lisa Roach in :issue:`33073` and Raymond Hettinger in 399 :issue:`37819`.) 400 401* Constructors of :class:`int`, :class:`float` and :class:`complex` will now 402 use the :meth:`~object.__index__` special method, if available and the 403 corresponding method :meth:`~object.__int__`, :meth:`~object.__float__` 404 or :meth:`~object.__complex__` is not available. 405 (Contributed by Serhiy Storchaka in :issue:`20092`.) 406 407* Added support of ``\N{name}`` escapes in :mod:`regular expressions <re>`:: 408 409 >>> notice = 'Copyright © 2019' 410 >>> copyright_year_pattern = re.compile(r'\N{copyright sign}\s*(\d{4})') 411 >>> int(copyright_year_pattern.search(notice).group(1)) 412 2019 413 414 (Contributed by Jonathan Eunice and Serhiy Storchaka in :issue:`30688`.) 415 416* Dict and dictviews are now iterable in reversed insertion order using 417 :func:`reversed`. (Contributed by Rémi Lapeyre in :issue:`33462`.) 418 419* The syntax allowed for keyword names in function calls was further 420 restricted. In particular, ``f((keyword)=arg)`` is no longer allowed. It was 421 never intended to permit more than a bare name on the left-hand side of a 422 keyword argument assignment term. 423 (Contributed by Benjamin Peterson in :issue:`34641`.) 424 425* Generalized iterable unpacking in :keyword:`yield` and 426 :keyword:`return` statements no longer requires enclosing parentheses. 427 This brings the *yield* and *return* syntax into better agreement with 428 normal assignment syntax:: 429 430 >>> def parse(family): 431 lastname, *members = family.split() 432 return lastname.upper(), *members 433 434 >>> parse('simpsons homer marge bart lisa maggie') 435 ('SIMPSONS', 'homer', 'marge', 'bart', 'lisa', 'maggie') 436 437 (Contributed by David Cuthbert and Jordan Chapman in :issue:`32117`.) 438 439* When a comma is missed in code such as ``[(10, 20) (30, 40)]``, the 440 compiler displays a :exc:`SyntaxWarning` with a helpful suggestion. 441 This improves on just having a :exc:`TypeError` indicating that the 442 first tuple was not callable. (Contributed by Serhiy Storchaka in 443 :issue:`15248`.) 444 445* Arithmetic operations between subclasses of :class:`datetime.date` or 446 :class:`datetime.datetime` and :class:`datetime.timedelta` objects now return 447 an instance of the subclass, rather than the base class. This also affects 448 the return type of operations whose implementation (directly or indirectly) 449 uses :class:`datetime.timedelta` arithmetic, such as 450 :meth:`~datetime.datetime.astimezone`. 451 (Contributed by Paul Ganssle in :issue:`32417`.) 452 453* When the Python interpreter is interrupted by Ctrl-C (SIGINT) and the 454 resulting :exc:`KeyboardInterrupt` exception is not caught, the Python process 455 now exits via a SIGINT signal or with the correct exit code such that the 456 calling process can detect that it died due to a Ctrl-C. Shells on POSIX 457 and Windows use this to properly terminate scripts in interactive sessions. 458 (Contributed by Google via Gregory P. Smith in :issue:`1054041`.) 459 460* Some advanced styles of programming require updating the 461 :class:`types.CodeType` object for an existing function. Since code 462 objects are immutable, a new code object needs to be created, one 463 that is modeled on the existing code object. With 19 parameters, 464 this was somewhat tedious. Now, the new ``replace()`` method makes 465 it possible to create a clone with a few altered parameters. 466 467 Here's an example that alters the :func:`statistics.mean` function to 468 prevent the *data* parameter from being used as a keyword argument:: 469 470 >>> from statistics import mean 471 >>> mean(data=[10, 20, 90]) 472 40 473 >>> mean.__code__ = mean.__code__.replace(co_posonlyargcount=1) 474 >>> mean(data=[10, 20, 90]) 475 Traceback (most recent call last): 476 ... 477 TypeError: mean() got some positional-only arguments passed as keyword arguments: 'data' 478 479 (Contributed by Victor Stinner in :issue:`37032`.) 480 481* For integers, the three-argument form of the :func:`pow` function now 482 permits the exponent to be negative in the case where the base is 483 relatively prime to the modulus. It then computes a modular inverse to 484 the base when the exponent is ``-1``, and a suitable power of that 485 inverse for other negative exponents. For example, to compute the 486 `modular multiplicative inverse 487 <https://en.wikipedia.org/wiki/Modular_multiplicative_inverse>`_ of 38 488 modulo 137, write:: 489 490 >>> pow(38, -1, 137) 491 119 492 >>> 119 * 38 % 137 493 1 494 495 Modular inverses arise in the solution of `linear Diophantine 496 equations <https://en.wikipedia.org/wiki/Diophantine_equation>`_. 497 For example, to find integer solutions for ``4258 + 147 = 369``, 498 first rewrite as ``4258 ≡ 369 (mod 147)`` then solve: 499 500 >>> x = 369 * pow(4258, -1, 147) % 147 501 >>> y = (4258 * x - 369) // -147 502 >>> 4258 * x + 147 * y 503 369 504 505 (Contributed by Mark Dickinson in :issue:`36027`.) 506 507* Dict comprehensions have been synced-up with dict literals so that the 508 key is computed first and the value second:: 509 510 >>> # Dict comprehension 511 >>> cast = {input('role? '): input('actor? ') for i in range(2)} 512 role? King Arthur 513 actor? Chapman 514 role? Black Knight 515 actor? Cleese 516 517 >>> # Dict literal 518 >>> cast = {input('role? '): input('actor? ')} 519 role? Sir Robin 520 actor? Eric Idle 521 522 The guaranteed execution order is helpful with assignment expressions 523 because variables assigned in the key expression will be available in 524 the value expression:: 525 526 >>> names = ['Martin von Löwis', 'Łukasz Langa', 'Walter Dörwald'] 527 >>> {(n := normalize('NFC', name)).casefold() : n for name in names} 528 {'martin von löwis': 'Martin von Löwis', 529 'łukasz langa': 'Łukasz Langa', 530 'walter dörwald': 'Walter Dörwald'} 531 532 (Contributed by Jörn Heissler in :issue:`35224`.) 533 534* The :meth:`object.__reduce__` method can now return a tuple from two to 535 six elements long. Formerly, five was the limit. The new, optional sixth 536 element is a callable with a ``(obj, state)`` signature. This allows the 537 direct control over the state-updating behavior of a specific object. If 538 not *None*, this callable will have priority over the object's 539 :meth:`~__setstate__` method. 540 (Contributed by Pierre Glaser and Olivier Grisel in :issue:`35900`.) 541 542New Modules 543=========== 544 545* The new :mod:`importlib.metadata` module provides (provisional) support for 546 reading metadata from third-party packages. For example, it can extract an 547 installed package's version number, list of entry points, and more:: 548 549 >>> # Note following example requires that the popular "requests" 550 >>> # package has been installed. 551 >>> 552 >>> from importlib.metadata import version, requires, files 553 >>> version('requests') 554 '2.22.0' 555 >>> list(requires('requests')) 556 ['chardet (<3.1.0,>=3.0.2)'] 557 >>> list(files('requests'))[:5] 558 [PackagePath('requests-2.22.0.dist-info/INSTALLER'), 559 PackagePath('requests-2.22.0.dist-info/LICENSE'), 560 PackagePath('requests-2.22.0.dist-info/METADATA'), 561 PackagePath('requests-2.22.0.dist-info/RECORD'), 562 PackagePath('requests-2.22.0.dist-info/WHEEL')] 563 564 (Contributed by Barry Warsaw and Jason R. Coombs in :issue:`34632`.) 565 566 567Improved Modules 568================ 569 570ast 571--- 572 573AST nodes now have ``end_lineno`` and ``end_col_offset`` attributes, 574which give the precise location of the end of the node. (This only 575applies to nodes that have ``lineno`` and ``col_offset`` attributes.) 576 577New function :func:`ast.get_source_segment` returns the source code 578for a specific AST node. 579 580(Contributed by Ivan Levkivskyi in :issue:`33416`.) 581 582The :func:`ast.parse` function has some new flags: 583 584* ``type_comments=True`` causes it to return the text of :pep:`484` and 585 :pep:`526` type comments associated with certain AST nodes; 586 587* ``mode='func_type'`` can be used to parse :pep:`484` "signature type 588 comments" (returned for function definition AST nodes); 589 590* ``feature_version=(3, N)`` allows specifying an earlier Python 3 591 version. For example, ``feature_version=(3, 4)`` will treat 592 :keyword:`async` and :keyword:`await` as non-reserved words. 593 594(Contributed by Guido van Rossum in :issue:`35766`.) 595 596 597asyncio 598------- 599 600:func:`asyncio.run` has graduated from the provisional to stable API. This 601function can be used to execute a :term:`coroutine` and return the result while 602automatically managing the event loop. For example:: 603 604 import asyncio 605 606 async def main(): 607 await asyncio.sleep(0) 608 return 42 609 610 asyncio.run(main()) 611 612This is *roughly* equivalent to:: 613 614 import asyncio 615 616 async def main(): 617 await asyncio.sleep(0) 618 return 42 619 620 loop = asyncio.new_event_loop() 621 asyncio.set_event_loop(loop) 622 try: 623 loop.run_until_complete(main()) 624 finally: 625 asyncio.set_event_loop(None) 626 loop.close() 627 628 629The actual implementation is significantly more complex. Thus, 630:func:`asyncio.run` should be the preferred way of running asyncio programs. 631 632(Contributed by Yury Selivanov in :issue:`32314`.) 633 634Running ``python -m asyncio`` launches a natively async REPL. This allows rapid 635experimentation with code that has a top-level :keyword:`await`. There is no 636longer a need to directly call ``asyncio.run()`` which would spawn a new event 637loop on every invocation: 638 639.. code-block:: none 640 641 $ python -m asyncio 642 asyncio REPL 3.8.0 643 Use "await" directly instead of "asyncio.run()". 644 Type "help", "copyright", "credits" or "license" for more information. 645 >>> import asyncio 646 >>> await asyncio.sleep(10, result='hello') 647 hello 648 649(Contributed by Yury Selivanov in :issue:`37028`.) 650 651The exception :class:`asyncio.CancelledError` now inherits from 652:class:`BaseException` rather than :class:`Exception` and no longer inherits 653from :class:`concurrent.futures.CancelledError`. 654(Contributed by Yury Selivanov in :issue:`32528`.) 655 656On Windows, the default event loop is now :class:`~asyncio.ProactorEventLoop`. 657(Contributed by Victor Stinner in :issue:`34687`.) 658 659:class:`~asyncio.ProactorEventLoop` now also supports UDP. 660(Contributed by Adam Meily and Andrew Svetlov in :issue:`29883`.) 661 662:class:`~asyncio.ProactorEventLoop` can now be interrupted by 663:exc:`KeyboardInterrupt` ("CTRL+C"). 664(Contributed by Vladimir Matveev in :issue:`23057`.) 665 666Added :meth:`asyncio.Task.get_coro` for getting the wrapped coroutine 667within an :class:`asyncio.Task`. 668(Contributed by Alex Grönholm in :issue:`36999`.) 669 670Asyncio tasks can now be named, either by passing the ``name`` keyword 671argument to :func:`asyncio.create_task` or 672the :meth:`~asyncio.loop.create_task` event loop method, or by 673calling the :meth:`~asyncio.Task.set_name` method on the task object. The 674task name is visible in the ``repr()`` output of :class:`asyncio.Task` and 675can also be retrieved using the :meth:`~asyncio.Task.get_name` method. 676(Contributed by Alex Grönholm in :issue:`34270`.) 677 678Added support for 679`Happy Eyeballs <https://en.wikipedia.org/wiki/Happy_Eyeballs>`_ to 680:func:`asyncio.loop.create_connection`. To specify the behavior, two new 681parameters have been added: *happy_eyeballs_delay* and *interleave*. The Happy 682Eyeballs algorithm improves responsiveness in applications that support IPv4 683and IPv6 by attempting to simultaneously connect using both. 684(Contributed by twisteroid ambassador in :issue:`33530`.) 685 686 687builtins 688-------- 689 690The :func:`compile` built-in has been improved to accept the 691``ast.PyCF_ALLOW_TOP_LEVEL_AWAIT`` flag. With this new flag passed, 692:func:`compile` will allow top-level ``await``, ``async for`` and ``async with`` 693constructs that are usually considered invalid syntax. Asynchronous code object 694marked with the ``CO_COROUTINE`` flag may then be returned. 695(Contributed by Matthias Bussonnier in :issue:`34616`) 696 697 698collections 699----------- 700 701The :meth:`~collections.somenamedtuple._asdict` method for 702:func:`collections.namedtuple` now returns a :class:`dict` instead of a 703:class:`collections.OrderedDict`. This works because regular dicts have 704guaranteed ordering since Python 3.7. If the extra features of 705:class:`OrderedDict` are required, the suggested remediation is to cast the 706result to the desired type: ``OrderedDict(nt._asdict())``. 707(Contributed by Raymond Hettinger in :issue:`35864`.) 708 709 710cProfile 711-------- 712 713The :class:`cProfile.Profile <profile.Profile>` class can now be used as a context manager. 714Profile a block of code by running:: 715 716 import cProfile 717 718 with cProfile.Profile() as profiler: 719 # code to be profiled 720 ... 721 722(Contributed by Scott Sanderson in :issue:`29235`.) 723 724 725csv 726--- 727 728The :class:`csv.DictReader` now returns instances of :class:`dict` instead of 729a :class:`collections.OrderedDict`. The tool is now faster and uses less 730memory while still preserving the field order. 731(Contributed by Michael Selik in :issue:`34003`.) 732 733 734curses 735------- 736 737Added a new variable holding structured version information for the 738underlying ncurses library: :data:`~curses.ncurses_version`. 739(Contributed by Serhiy Storchaka in :issue:`31680`.) 740 741 742ctypes 743------ 744 745On Windows, :class:`~ctypes.CDLL` and subclasses now accept a *winmode* parameter 746to specify flags for the underlying ``LoadLibraryEx`` call. The default flags are 747set to only load DLL dependencies from trusted locations, including the path 748where the DLL is stored (if a full or partial path is used to load the initial 749DLL) and paths added by :func:`~os.add_dll_directory`. 750(Contributed by Steve Dower in :issue:`36085`.) 751 752 753datetime 754-------- 755 756Added new alternate constructors :meth:`datetime.date.fromisocalendar` and 757:meth:`datetime.datetime.fromisocalendar`, which construct :class:`date` and 758:class:`datetime` objects respectively from ISO year, week number, and weekday; 759these are the inverse of each class's ``isocalendar`` method. 760(Contributed by Paul Ganssle in :issue:`36004`.) 761 762 763functools 764--------- 765 766:func:`functools.lru_cache` can now be used as a straight decorator rather 767than as a function returning a decorator. So both of these are now supported:: 768 769 @lru_cache 770 def f(x): 771 ... 772 773 @lru_cache(maxsize=256) 774 def f(x): 775 ... 776 777(Contributed by Raymond Hettinger in :issue:`36772`.) 778 779Added a new :func:`functools.cached_property` decorator, for computed properties 780cached for the life of the instance. :: 781 782 import functools 783 import statistics 784 785 class Dataset: 786 def __init__(self, sequence_of_numbers): 787 self.data = sequence_of_numbers 788 789 @functools.cached_property 790 def variance(self): 791 return statistics.variance(self.data) 792 793(Contributed by Carl Meyer in :issue:`21145`) 794 795 796Added a new :func:`functools.singledispatchmethod` decorator that converts 797methods into :term:`generic functions <generic function>` using 798:term:`single dispatch`:: 799 800 from functools import singledispatchmethod 801 from contextlib import suppress 802 803 class TaskManager: 804 805 def __init__(self, tasks): 806 self.tasks = list(tasks) 807 808 @singledispatchmethod 809 def discard(self, value): 810 with suppress(ValueError): 811 self.tasks.remove(value) 812 813 @discard.register(list) 814 def _(self, tasks): 815 targets = set(tasks) 816 self.tasks = [x for x in self.tasks if x not in targets] 817 818(Contributed by Ethan Smith in :issue:`32380`) 819 820gc 821-- 822 823:func:`~gc.get_objects` can now receive an optional *generation* parameter 824indicating a generation to get objects from. 825(Contributed by Pablo Galindo in :issue:`36016`.) 826 827 828gettext 829------- 830 831Added :func:`~gettext.pgettext` and its variants. 832(Contributed by Franz Glasner, Éric Araujo, and Cheryl Sabella in :issue:`2504`.) 833 834 835gzip 836---- 837 838Added the *mtime* parameter to :func:`gzip.compress` for reproducible output. 839(Contributed by Guo Ci Teo in :issue:`34898`.) 840 841A :exc:`~gzip.BadGzipFile` exception is now raised instead of :exc:`OSError` 842for certain types of invalid or corrupt gzip files. 843(Contributed by Filip Gruszczyński, Michele Orrù, and Zackery Spytz in 844:issue:`6584`.) 845 846 847IDLE and idlelib 848---------------- 849 850Output over N lines (50 by default) is squeezed down to a button. 851N can be changed in the PyShell section of the General page of the 852Settings dialog. Fewer, but possibly extra long, lines can be squeezed by 853right clicking on the output. Squeezed output can be expanded in place 854by double-clicking the button or into the clipboard or a separate window 855by right-clicking the button. (Contributed by Tal Einat in :issue:`1529353`.) 856 857Add "Run Customized" to the Run menu to run a module with customized 858settings. Any command line arguments entered are added to sys.argv. 859They also re-appear in the box for the next customized run. One can also 860suppress the normal Shell main module restart. (Contributed by Cheryl 861Sabella, Terry Jan Reedy, and others in :issue:`5680` and :issue:`37627`.) 862 863Added optional line numbers for IDLE editor windows. Windows 864open without line numbers unless set otherwise in the General 865tab of the configuration dialog. Line numbers for an existing 866window are shown and hidden in the Options menu. 867(Contributed by Tal Einat and Saimadhav Heblikar in :issue:`17535`.) 868 869OS native encoding is now used for converting between Python strings and Tcl 870objects. This allows IDLE to work with emoji and other non-BMP characters. 871These characters can be displayed or copied and pasted to or from the 872clipboard. Converting strings from Tcl to Python and back now never fails. 873(Many people worked on this for eight years but the problem was finally 874solved by Serhiy Storchaka in :issue:`13153`.) 875 876New in 3.8.1: 877 878Add option to toggle cursor blink off. (Contributed by Zackery Spytz 879in :issue:`4603`.) 880 881Escape key now closes IDLE completion windows. (Contributed by Johnny 882Najera in :issue:`38944`.) 883 884The changes above have been backported to 3.7 maintenance releases. 885 886Add keywords to module name completion list. (Contributed by Terry J. 887Reedy in :issue:`37765`.) 888 889inspect 890------- 891 892The :func:`inspect.getdoc` function can now find docstrings for ``__slots__`` 893if that attribute is a :class:`dict` where the values are docstrings. 894This provides documentation options similar to what we already have 895for :func:`property`, :func:`classmethod`, and :func:`staticmethod`:: 896 897 class AudioClip: 898 __slots__ = {'bit_rate': 'expressed in kilohertz to one decimal place', 899 'duration': 'in seconds, rounded up to an integer'} 900 def __init__(self, bit_rate, duration): 901 self.bit_rate = round(bit_rate / 1000.0, 1) 902 self.duration = ceil(duration) 903 904(Contributed by Raymond Hettinger in :issue:`36326`.) 905 906 907io 908-- 909 910In development mode (:option:`-X` ``env``) and in :ref:`debug build <debug-build>`, the 911:class:`io.IOBase` finalizer now logs the exception if the ``close()`` method 912fails. The exception is ignored silently by default in release build. 913(Contributed by Victor Stinner in :issue:`18748`.) 914 915 916itertools 917--------- 918 919The :func:`itertools.accumulate` function added an option *initial* keyword 920argument to specify an initial value:: 921 922 >>> from itertools import accumulate 923 >>> list(accumulate([10, 5, 30, 15], initial=1000)) 924 [1000, 1010, 1015, 1045, 1060] 925 926(Contributed by Lisa Roach in :issue:`34659`.) 927 928 929json.tool 930--------- 931 932Add option ``--json-lines`` to parse every input line as a separate JSON object. 933(Contributed by Weipeng Hong in :issue:`31553`.) 934 935 936logging 937------- 938 939Added a *force* keyword argument to :func:`logging.basicConfig()` 940When set to true, any existing handlers attached 941to the root logger are removed and closed before carrying out the 942configuration specified by the other arguments. 943 944This solves a long-standing problem. Once a logger or *basicConfig()* had 945been called, subsequent calls to *basicConfig()* were silently ignored. 946This made it difficult to update, experiment with, or teach the various 947logging configuration options using the interactive prompt or a Jupyter 948notebook. 949 950(Suggested by Raymond Hettinger, implemented by Dong-hee Na, and 951reviewed by Vinay Sajip in :issue:`33897`.) 952 953 954math 955---- 956 957Added new function :func:`math.dist` for computing Euclidean distance 958between two points. (Contributed by Raymond Hettinger in :issue:`33089`.) 959 960Expanded the :func:`math.hypot` function to handle multiple dimensions. 961Formerly, it only supported the 2-D case. 962(Contributed by Raymond Hettinger in :issue:`33089`.) 963 964Added new function, :func:`math.prod`, as analogous function to :func:`sum` 965that returns the product of a 'start' value (default: 1) times an iterable of 966numbers:: 967 968 >>> prior = 0.8 969 >>> likelihoods = [0.625, 0.84, 0.30] 970 >>> math.prod(likelihoods, start=prior) 971 0.126 972 973(Contributed by Pablo Galindo in :issue:`35606`.) 974 975Added two new combinatoric functions :func:`math.perm` and :func:`math.comb`:: 976 977 >>> math.perm(10, 3) # Permutations of 10 things taken 3 at a time 978 720 979 >>> math.comb(10, 3) # Combinations of 10 things taken 3 at a time 980 120 981 982(Contributed by Yash Aggarwal, Keller Fuchs, Serhiy Storchaka, and Raymond 983Hettinger in :issue:`37128`, :issue:`37178`, and :issue:`35431`.) 984 985Added a new function :func:`math.isqrt` for computing accurate integer square 986roots without conversion to floating point. The new function supports 987arbitrarily large integers. It is faster than ``floor(sqrt(n))`` but slower 988than :func:`math.sqrt`:: 989 990 >>> r = 650320427 991 >>> s = r ** 2 992 >>> isqrt(s - 1) # correct 993 650320426 994 >>> floor(sqrt(s - 1)) # incorrect 995 650320427 996 997(Contributed by Mark Dickinson in :issue:`36887`.) 998 999The function :func:`math.factorial` no longer accepts arguments that are not 1000int-like. (Contributed by Pablo Galindo in :issue:`33083`.) 1001 1002 1003mmap 1004---- 1005 1006The :class:`mmap.mmap` class now has an :meth:`~mmap.mmap.madvise` method to 1007access the ``madvise()`` system call. 1008(Contributed by Zackery Spytz in :issue:`32941`.) 1009 1010 1011multiprocessing 1012--------------- 1013 1014Added new :mod:`multiprocessing.shared_memory` module. 1015(Contributed by Davin Potts in :issue:`35813`.) 1016 1017On macOS, the *spawn* start method is now used by default. 1018(Contributed by Victor Stinner in :issue:`33725`.) 1019 1020 1021os 1022-- 1023 1024Added new function :func:`~os.add_dll_directory` on Windows for providing 1025additional search paths for native dependencies when importing extension 1026modules or loading DLLs using :mod:`ctypes`. 1027(Contributed by Steve Dower in :issue:`36085`.) 1028 1029A new :func:`os.memfd_create` function was added to wrap the 1030``memfd_create()`` syscall. 1031(Contributed by Zackery Spytz and Christian Heimes in :issue:`26836`.) 1032 1033On Windows, much of the manual logic for handling reparse points (including 1034symlinks and directory junctions) has been delegated to the operating system. 1035Specifically, :func:`os.stat` will now traverse anything supported by the 1036operating system, while :func:`os.lstat` will only open reparse points that 1037identify as "name surrogates" while others are opened as for :func:`os.stat`. 1038In all cases, :attr:`stat_result.st_mode` will only have ``S_IFLNK`` set for 1039symbolic links and not other kinds of reparse points. To identify other kinds 1040of reparse point, check the new :attr:`stat_result.st_reparse_tag` attribute. 1041 1042On Windows, :func:`os.readlink` is now able to read directory junctions. Note 1043that :func:`~os.path.islink` will return ``False`` for directory junctions, 1044and so code that checks ``islink`` first will continue to treat junctions as 1045directories, while code that handles errors from :func:`os.readlink` may now 1046treat junctions as links. 1047 1048(Contributed by Steve Dower in :issue:`37834`.) 1049 1050 1051os.path 1052------- 1053 1054:mod:`os.path` functions that return a boolean result like 1055:func:`~os.path.exists`, :func:`~os.path.lexists`, :func:`~os.path.isdir`, 1056:func:`~os.path.isfile`, :func:`~os.path.islink`, and :func:`~os.path.ismount` 1057now return ``False`` instead of raising :exc:`ValueError` or its subclasses 1058:exc:`UnicodeEncodeError` and :exc:`UnicodeDecodeError` for paths that contain 1059characters or bytes unrepresentable at the OS level. 1060(Contributed by Serhiy Storchaka in :issue:`33721`.) 1061 1062:func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE` 1063environment variable and does not use :envvar:`HOME`, which is not normally set 1064for regular user accounts. 1065(Contributed by Anthony Sottile in :issue:`36264`.) 1066 1067:func:`~os.path.isdir` on Windows no longer returns ``True`` for a link to a 1068non-existent directory. 1069 1070:func:`~os.path.realpath` on Windows now resolves reparse points, including 1071symlinks and directory junctions. 1072 1073(Contributed by Steve Dower in :issue:`37834`.) 1074 1075 1076pathlib 1077------- 1078 1079:mod:`pathlib.Path` methods that return a boolean result like 1080:meth:`~pathlib.Path.exists()`, :meth:`~pathlib.Path.is_dir()`, 1081:meth:`~pathlib.Path.is_file()`, :meth:`~pathlib.Path.is_mount()`, 1082:meth:`~pathlib.Path.is_symlink()`, :meth:`~pathlib.Path.is_block_device()`, 1083:meth:`~pathlib.Path.is_char_device()`, :meth:`~pathlib.Path.is_fifo()`, 1084:meth:`~pathlib.Path.is_socket()` now return ``False`` instead of raising 1085:exc:`ValueError` or its subclass :exc:`UnicodeEncodeError` for paths that 1086contain characters unrepresentable at the OS level. 1087(Contributed by Serhiy Storchaka in :issue:`33721`.) 1088 1089Added :meth:`pathlib.Path.link_to()` which creates a hard link pointing 1090to a path. 1091(Contributed by Joannah Nanjekye in :issue:`26978`) 1092 1093 1094pickle 1095------ 1096 1097:mod:`pickle` extensions subclassing the C-optimized :class:`~pickle.Pickler` 1098can now override the pickling logic of functions and classes by defining the 1099special :meth:`~pickle.Pickler.reducer_override` method. 1100(Contributed by Pierre Glaser and Olivier Grisel in :issue:`35900`.) 1101 1102 1103plistlib 1104-------- 1105 1106Added new :class:`plistlib.UID` and enabled support for reading and writing 1107NSKeyedArchiver-encoded binary plists. 1108(Contributed by Jon Janzen in :issue:`26707`.) 1109 1110 1111pprint 1112------ 1113 1114The :mod:`pprint` module added a *sort_dicts* parameter to several functions. 1115By default, those functions continue to sort dictionaries before rendering or 1116printing. However, if *sort_dicts* is set to false, the dictionaries retain 1117the order that keys were inserted. This can be useful for comparison to JSON 1118inputs during debugging. 1119 1120In addition, there is a convenience new function, :func:`pprint.pp` that is 1121like :func:`pprint.pprint` but with *sort_dicts* defaulting to ``False``:: 1122 1123 >>> from pprint import pprint, pp 1124 >>> d = dict(source='input.txt', operation='filter', destination='output.txt') 1125 >>> pp(d, width=40) # Original order 1126 {'source': 'input.txt', 1127 'operation': 'filter', 1128 'destination': 'output.txt'} 1129 >>> pprint(d, width=40) # Keys sorted alphabetically 1130 {'destination': 'output.txt', 1131 'operation': 'filter', 1132 'source': 'input.txt'} 1133 1134(Contributed by Rémi Lapeyre in :issue:`30670`.) 1135 1136 1137py_compile 1138---------- 1139 1140:func:`py_compile.compile` now supports silent mode. 1141(Contributed by Joannah Nanjekye in :issue:`22640`.) 1142 1143 1144shlex 1145----- 1146 1147The new :func:`shlex.join` function acts as the inverse of :func:`shlex.split`. 1148(Contributed by Bo Bayles in :issue:`32102`.) 1149 1150 1151shutil 1152------ 1153 1154:func:`shutil.copytree` now accepts a new ``dirs_exist_ok`` keyword argument. 1155(Contributed by Josh Bronson in :issue:`20849`.) 1156 1157:func:`shutil.make_archive` now defaults to the modern pax (POSIX.1-2001) 1158format for new archives to improve portability and standards conformance, 1159inherited from the corresponding change to the :mod:`tarfile` module. 1160(Contributed by C.A.M. Gerlach in :issue:`30661`.) 1161 1162:func:`shutil.rmtree` on Windows now removes directory junctions without 1163recursively removing their contents first. 1164(Contributed by Steve Dower in :issue:`37834`.) 1165 1166 1167socket 1168------ 1169 1170Added :meth:`~socket.create_server()` and :meth:`~socket.has_dualstack_ipv6()` 1171convenience functions to automate the necessary tasks usually involved when 1172creating a server socket, including accepting both IPv4 and IPv6 connections 1173on the same socket. (Contributed by Giampaolo Rodolà in :issue:`17561`.) 1174 1175The :func:`socket.if_nameindex()`, :func:`socket.if_nametoindex()`, and 1176:func:`socket.if_indextoname()` functions have been implemented on Windows. 1177(Contributed by Zackery Spytz in :issue:`37007`.) 1178 1179 1180ssl 1181--- 1182 1183Added :attr:`~ssl.SSLContext.post_handshake_auth` to enable and 1184:meth:`~ssl.SSLSocket.verify_client_post_handshake` to initiate TLS 1.3 1185post-handshake authentication. 1186(Contributed by Christian Heimes in :issue:`34670`.) 1187 1188 1189statistics 1190---------- 1191 1192Added :func:`statistics.fmean` as a faster, floating point variant of 1193:func:`statistics.mean()`. (Contributed by Raymond Hettinger and 1194Steven D'Aprano in :issue:`35904`.) 1195 1196Added :func:`statistics.geometric_mean()` 1197(Contributed by Raymond Hettinger in :issue:`27181`.) 1198 1199Added :func:`statistics.multimode` that returns a list of the most 1200common values. (Contributed by Raymond Hettinger in :issue:`35892`.) 1201 1202Added :func:`statistics.quantiles` that divides data or a distribution 1203in to equiprobable intervals (e.g. quartiles, deciles, or percentiles). 1204(Contributed by Raymond Hettinger in :issue:`36546`.) 1205 1206Added :class:`statistics.NormalDist`, a tool for creating 1207and manipulating normal distributions of a random variable. 1208(Contributed by Raymond Hettinger in :issue:`36018`.) 1209 1210:: 1211 1212 >>> temperature_feb = NormalDist.from_samples([4, 12, -3, 2, 7, 14]) 1213 >>> temperature_feb.mean 1214 6.0 1215 >>> temperature_feb.stdev 1216 6.356099432828281 1217 1218 >>> temperature_feb.cdf(3) # Chance of being under 3 degrees 1219 0.3184678262814532 1220 >>> # Relative chance of being 7 degrees versus 10 degrees 1221 >>> temperature_feb.pdf(7) / temperature_feb.pdf(10) 1222 1.2039930378537762 1223 1224 >>> el_niño = NormalDist(4, 2.5) 1225 >>> temperature_feb += el_niño # Add in a climate effect 1226 >>> temperature_feb 1227 NormalDist(mu=10.0, sigma=6.830080526611674) 1228 1229 >>> temperature_feb * (9/5) + 32 # Convert to Fahrenheit 1230 NormalDist(mu=50.0, sigma=12.294144947901014) 1231 >>> temperature_feb.samples(3) # Generate random samples 1232 [7.672102882379219, 12.000027119750287, 4.647488369766392] 1233 1234 1235sys 1236--- 1237 1238Add new :func:`sys.unraisablehook` function which can be overridden to control 1239how "unraisable exceptions" are handled. It is called when an exception has 1240occurred but there is no way for Python to handle it. For example, when a 1241destructor raises an exception or during garbage collection 1242(:func:`gc.collect`). 1243(Contributed by Victor Stinner in :issue:`36829`.) 1244 1245 1246tarfile 1247------- 1248 1249The :mod:`tarfile` module now defaults to the modern pax (POSIX.1-2001) 1250format for new archives, instead of the previous GNU-specific one. 1251This improves cross-platform portability with a consistent encoding (UTF-8) 1252in a standardized and extensible format, and offers several other benefits. 1253(Contributed by C.A.M. Gerlach in :issue:`36268`.) 1254 1255 1256threading 1257--------- 1258 1259Add a new :func:`threading.excepthook` function which handles uncaught 1260:meth:`threading.Thread.run` exception. It can be overridden to control how 1261uncaught :meth:`threading.Thread.run` exceptions are handled. 1262(Contributed by Victor Stinner in :issue:`1230540`.) 1263 1264Add a new :func:`threading.get_native_id` function and 1265a :data:`~threading.Thread.native_id` 1266attribute to the :class:`threading.Thread` class. These return the native 1267integral Thread ID of the current thread assigned by the kernel. 1268This feature is only available on certain platforms, see 1269:func:`get_native_id <threading.get_native_id>` for more information. 1270(Contributed by Jake Tesler in :issue:`36084`.) 1271 1272 1273tokenize 1274-------- 1275 1276The :mod:`tokenize` module now implicitly emits a ``NEWLINE`` token when 1277provided with input that does not have a trailing new line. This behavior 1278now matches what the C tokenizer does internally. 1279(Contributed by Ammar Askar in :issue:`33899`.) 1280 1281 1282tkinter 1283------- 1284 1285Added methods :meth:`~tkinter.Spinbox.selection_from`, 1286:meth:`~tkinter.Spinbox.selection_present`, 1287:meth:`~tkinter.Spinbox.selection_range` and 1288:meth:`~tkinter.Spinbox.selection_to` 1289in the :class:`tkinter.Spinbox` class. 1290(Contributed by Juliette Monsel in :issue:`34829`.) 1291 1292Added method :meth:`~tkinter.Canvas.moveto` 1293in the :class:`tkinter.Canvas` class. 1294(Contributed by Juliette Monsel in :issue:`23831`.) 1295 1296The :class:`tkinter.PhotoImage` class now has 1297:meth:`~tkinter.PhotoImage.transparency_get` and 1298:meth:`~tkinter.PhotoImage.transparency_set` methods. (Contributed by 1299Zackery Spytz in :issue:`25451`.) 1300 1301 1302time 1303---- 1304 1305Added new clock :data:`~time.CLOCK_UPTIME_RAW` for macOS 10.12. 1306(Contributed by Joannah Nanjekye in :issue:`35702`.) 1307 1308 1309typing 1310------ 1311 1312The :mod:`typing` module incorporates several new features: 1313 1314* A dictionary type with per-key types. See :pep:`589` and 1315 :class:`typing.TypedDict`. 1316 TypedDict uses only string keys. By default, every key is required 1317 to be present. Specify "total=False" to allow keys to be optional:: 1318 1319 class Location(TypedDict, total=False): 1320 lat_long: tuple 1321 grid_square: str 1322 xy_coordinate: tuple 1323 1324* Literal types. See :pep:`586` and :class:`typing.Literal`. 1325 Literal types indicate that a parameter or return value 1326 is constrained to one or more specific literal values:: 1327 1328 def get_status(port: int) -> Literal['connected', 'disconnected']: 1329 ... 1330 1331* "Final" variables, functions, methods and classes. See :pep:`591`, 1332 :class:`typing.Final` and :func:`typing.final`. 1333 The final qualifier instructs a static type checker to restrict 1334 subclassing, overriding, or reassignment:: 1335 1336 pi: Final[float] = 3.1415926536 1337 1338* Protocol definitions. See :pep:`544`, :class:`typing.Protocol` and 1339 :func:`typing.runtime_checkable`. Simple ABCs like 1340 :class:`typing.SupportsInt` are now ``Protocol`` subclasses. 1341 1342* New protocol class :class:`typing.SupportsIndex`. 1343 1344* New functions :func:`typing.get_origin` and :func:`typing.get_args`. 1345 1346 1347unicodedata 1348----------- 1349 1350The :mod:`unicodedata` module has been upgraded to use the `Unicode 12.1.0 1351<https://blog.unicode.org/2019/05/unicode-12-1-en.html>`_ release. 1352 1353New function :func:`~unicodedata.is_normalized` can be used to verify a string 1354is in a specific normal form, often much faster than by actually normalizing 1355the string. (Contributed by Max Belanger, David Euresti, and Greg Price in 1356:issue:`32285` and :issue:`37966`). 1357 1358 1359unittest 1360-------- 1361 1362Added :class:`~unittest.mock.AsyncMock` to support an asynchronous version of 1363:class:`~unittest.mock.Mock`. Appropriate new assert functions for testing 1364have been added as well. 1365(Contributed by Lisa Roach in :issue:`26467`). 1366 1367Added :func:`~unittest.addModuleCleanup()` and 1368:meth:`~unittest.TestCase.addClassCleanup()` to unittest to support 1369cleanups for :func:`~unittest.setUpModule()` and 1370:meth:`~unittest.TestCase.setUpClass()`. 1371(Contributed by Lisa Roach in :issue:`24412`.) 1372 1373Several mock assert functions now also print a list of actual calls upon 1374failure. (Contributed by Petter Strandmark in :issue:`35047`.) 1375 1376:mod:`unittest` module gained support for coroutines to be used as test cases 1377with :class:`unittest.IsolatedAsyncioTestCase`. 1378(Contributed by Andrew Svetlov in :issue:`32972`.) 1379 1380Example:: 1381 1382 import unittest 1383 1384 1385 class TestRequest(unittest.IsolatedAsyncioTestCase): 1386 1387 async def asyncSetUp(self): 1388 self.connection = await AsyncConnection() 1389 1390 async def test_get(self): 1391 response = await self.connection.get("https://example.com") 1392 self.assertEqual(response.status_code, 200) 1393 1394 async def asyncTearDown(self): 1395 await self.connection.close() 1396 1397 1398 if __name__ == "__main__": 1399 unittest.main() 1400 1401 1402venv 1403---- 1404 1405:mod:`venv` now includes an ``Activate.ps1`` script on all platforms for 1406activating virtual environments under PowerShell Core 6.1. 1407(Contributed by Brett Cannon in :issue:`32718`.) 1408 1409 1410weakref 1411------- 1412 1413The proxy objects returned by :func:`weakref.proxy` now support the matrix 1414multiplication operators ``@`` and ``@=`` in addition to the other 1415numeric operators. (Contributed by Mark Dickinson in :issue:`36669`.) 1416 1417 1418xml 1419--- 1420 1421As mitigation against DTD and external entity retrieval, the 1422:mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process 1423external entities by default. 1424(Contributed by Christian Heimes in :issue:`17239`.) 1425 1426The ``.find*()`` methods in the :mod:`xml.etree.ElementTree` module 1427support wildcard searches like ``{*}tag`` which ignores the namespace 1428and ``{namespace}*`` which returns all tags in the given namespace. 1429(Contributed by Stefan Behnel in :issue:`28238`.) 1430 1431The :mod:`xml.etree.ElementTree` module provides a new function 1432:func:`–xml.etree.ElementTree.canonicalize()` that implements C14N 2.0. 1433(Contributed by Stefan Behnel in :issue:`13611`.) 1434 1435The target object of :class:`xml.etree.ElementTree.XMLParser` can 1436receive namespace declaration events through the new callback methods 1437``start_ns()`` and ``end_ns()``. Additionally, the 1438:class:`xml.etree.ElementTree.TreeBuilder` target can be configured 1439to process events about comments and processing instructions to include 1440them in the generated tree. 1441(Contributed by Stefan Behnel in :issue:`36676` and :issue:`36673`.) 1442 1443 1444xmlrpc 1445------ 1446 1447:class:`xmlrpc.client.ServerProxy` now supports an optional *headers* keyword 1448argument for a sequence of HTTP headers to be sent with each request. Among 1449other things, this makes it possible to upgrade from default basic 1450authentication to faster session authentication. 1451(Contributed by Cédric Krier in :issue:`35153`.) 1452 1453 1454Optimizations 1455============= 1456 1457* The :mod:`subprocess` module can now use the :func:`os.posix_spawn` function 1458 in some cases for better performance. Currently, it is only used on macOS 1459 and Linux (using glibc 2.24 or newer) if all these conditions are met: 1460 1461 * *close_fds* is false; 1462 * *preexec_fn*, *pass_fds*, *cwd* and *start_new_session* parameters 1463 are not set; 1464 * the *executable* path contains a directory. 1465 1466 (Contributed by Joannah Nanjekye and Victor Stinner in :issue:`35537`.) 1467 1468* :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`, 1469 :func:`shutil.copytree` and :func:`shutil.move` use platform-specific 1470 "fast-copy" syscalls on Linux and macOS in order to copy the file 1471 more efficiently. 1472 "fast-copy" means that the copying operation occurs within the kernel, 1473 avoiding the use of userspace buffers in Python as in 1474 "``outfd.write(infd.read())``". 1475 On Windows :func:`shutil.copyfile` uses a bigger default buffer size (1 MiB 1476 instead of 16 KiB) and a :func:`memoryview`-based variant of 1477 :func:`shutil.copyfileobj` is used. 1478 The speedup for copying a 512 MiB file within the same partition is about 1479 +26% on Linux, +50% on macOS and +40% on Windows. Also, much less CPU cycles 1480 are consumed. 1481 See :ref:`shutil-platform-dependent-efficient-copy-operations` section. 1482 (Contributed by Giampaolo Rodolà in :issue:`33671`.) 1483 1484* :func:`shutil.copytree` uses :func:`os.scandir` function and all copy 1485 functions depending from it use cached :func:`os.stat` values. The speedup 1486 for copying a directory with 8000 files is around +9% on Linux, +20% on 1487 Windows and +30% on a Windows SMB share. Also the number of :func:`os.stat` 1488 syscalls is reduced by 38% making :func:`shutil.copytree` especially faster 1489 on network filesystems. (Contributed by Giampaolo Rodolà in :issue:`33695`.) 1490 1491* The default protocol in the :mod:`pickle` module is now Protocol 4, 1492 first introduced in Python 3.4. It offers better performance and smaller 1493 size compared to Protocol 3 available since Python 3.0. 1494 1495* Removed one :c:type:`Py_ssize_t` member from ``PyGC_Head``. All GC tracked 1496 objects (e.g. tuple, list, dict) size is reduced 4 or 8 bytes. 1497 (Contributed by Inada Naoki in :issue:`33597`.) 1498 1499* :class:`uuid.UUID` now uses ``__slots__`` to reduce its memory footprint. 1500 (Contributed by Wouter Bolsterlee and Tal Einat in :issue:`30977`) 1501 1502* Improved performance of :func:`operator.itemgetter` by 33%. Optimized 1503 argument handling and added a fast path for the common case of a single 1504 non-negative integer index into a tuple (which is the typical use case in 1505 the standard library). (Contributed by Raymond Hettinger in 1506 :issue:`35664`.) 1507 1508* Sped-up field lookups in :func:`collections.namedtuple`. They are now more 1509 than two times faster, making them the fastest form of instance variable 1510 lookup in Python. (Contributed by Raymond Hettinger, Pablo Galindo, and 1511 Joe Jevnik, Serhiy Storchaka in :issue:`32492`.) 1512 1513* The :class:`list` constructor does not overallocate the internal item buffer 1514 if the input iterable has a known length (the input implements ``__len__``). 1515 This makes the created list 12% smaller on average. (Contributed by 1516 Raymond Hettinger and Pablo Galindo in :issue:`33234`.) 1517 1518* Doubled the speed of class variable writes. When a non-dunder attribute 1519 was updated, there was an unnecessary call to update slots. 1520 (Contributed by Stefan Behnel, Pablo Galindo Salgado, Raymond Hettinger, 1521 Neil Schemenauer, and Serhiy Storchaka in :issue:`36012`.) 1522 1523* Reduced an overhead of converting arguments passed to many builtin functions 1524 and methods. This sped up calling some simple builtin functions and 1525 methods up to 20--50%. (Contributed by Serhiy Storchaka in :issue:`23867`, 1526 :issue:`35582` and :issue:`36127`.) 1527 1528* ``LOAD_GLOBAL`` instruction now uses new "per opcode cache" mechanism. 1529 It is about 40% faster now. (Contributed by Yury Selivanov and Inada Naoki in 1530 :issue:`26219`.) 1531 1532 1533Build and C API Changes 1534======================= 1535 1536* Default :data:`sys.abiflags` became an empty string: the ``m`` flag for 1537 pymalloc became useless (builds with and without pymalloc are ABI compatible) 1538 and so has been removed. (Contributed by Victor Stinner in :issue:`36707`.) 1539 1540 Example of changes: 1541 1542 * Only ``python3.8`` program is installed, ``python3.8m`` program is gone. 1543 * Only ``python3.8-config`` script is installed, ``python3.8m-config`` script 1544 is gone. 1545 * The ``m`` flag has been removed from the suffix of dynamic library 1546 filenames: extension modules in the standard library as well as those 1547 produced and installed by third-party packages, like those downloaded from 1548 PyPI. On Linux, for example, the Python 3.7 suffix 1549 ``.cpython-37m-x86_64-linux-gnu.so`` became 1550 ``.cpython-38-x86_64-linux-gnu.so`` in Python 3.8. 1551 1552* The header files have been reorganized to better separate the different kinds 1553 of APIs: 1554 1555 * ``Include/*.h`` should be the portable public stable C API. 1556 * ``Include/cpython/*.h`` should be the unstable C API specific to CPython; 1557 public API, with some private API prefixed by ``_Py`` or ``_PY``. 1558 * ``Include/internal/*.h`` is the private internal C API very specific to 1559 CPython. This API comes with no backward compatibility warranty and should 1560 not be used outside CPython. It is only exposed for very specific needs 1561 like debuggers and profiles which has to access to CPython internals 1562 without calling functions. This API is now installed by ``make install``. 1563 1564 (Contributed by Victor Stinner in :issue:`35134` and :issue:`35081`, 1565 work initiated by Eric Snow in Python 3.7.) 1566 1567* Some macros have been converted to static inline functions: parameter types 1568 and return type are well defined, they don't have issues specific to macros, 1569 variables have a local scopes. Examples: 1570 1571 * :c:func:`Py_INCREF`, :c:func:`Py_DECREF` 1572 * :c:func:`Py_XINCREF`, :c:func:`Py_XDECREF` 1573 * :c:func:`PyObject_INIT`, :c:func:`PyObject_INIT_VAR` 1574 * Private functions: :c:func:`_PyObject_GC_TRACK`, 1575 :c:func:`_PyObject_GC_UNTRACK`, :c:func:`_Py_Dealloc` 1576 1577 (Contributed by Victor Stinner in :issue:`35059`.) 1578 1579* The :c:func:`PyByteArray_Init` and :c:func:`PyByteArray_Fini` functions have 1580 been removed. They did nothing since Python 2.7.4 and Python 3.2.0, were 1581 excluded from the limited API (stable ABI), and were not documented. 1582 (Contributed by Victor Stinner in :issue:`35713`.) 1583 1584* The result of :c:func:`PyExceptionClass_Name` is now of type 1585 ``const char *`` rather of ``char *``. 1586 (Contributed by Serhiy Storchaka in :issue:`33818`.) 1587 1588* The duality of ``Modules/Setup.dist`` and ``Modules/Setup`` has been 1589 removed. Previously, when updating the CPython source tree, one had 1590 to manually copy ``Modules/Setup.dist`` (inside the source tree) to 1591 ``Modules/Setup`` (inside the build tree) in order to reflect any changes 1592 upstream. This was of a small benefit to packagers at the expense of 1593 a frequent annoyance to developers following CPython development, as 1594 forgetting to copy the file could produce build failures. 1595 1596 Now the build system always reads from ``Modules/Setup`` inside the source 1597 tree. People who want to customize that file are encouraged to maintain 1598 their changes in a git fork of CPython or as patch files, as they would do 1599 for any other change to the source tree. 1600 1601 (Contributed by Antoine Pitrou in :issue:`32430`.) 1602 1603* Functions that convert Python number to C integer like 1604 :c:func:`PyLong_AsLong` and argument parsing functions like 1605 :c:func:`PyArg_ParseTuple` with integer converting format units like ``'i'`` 1606 will now use the :meth:`~object.__index__` special method instead of 1607 :meth:`~object.__int__`, if available. The deprecation warning will be 1608 emitted for objects with the ``__int__()`` method but without the 1609 ``__index__()`` method (like :class:`~decimal.Decimal` and 1610 :class:`~fractions.Fraction`). :c:func:`PyNumber_Check` will now return 1611 ``1`` for objects implementing ``__index__()``. 1612 :c:func:`PyNumber_Long`, :c:func:`PyNumber_Float` and 1613 :c:func:`PyFloat_AsDouble` also now use the ``__index__()`` method if 1614 available. 1615 (Contributed by Serhiy Storchaka in :issue:`36048` and :issue:`20092`.) 1616 1617* Heap-allocated type objects will now increase their reference count 1618 in :c:func:`PyObject_Init` (and its parallel macro ``PyObject_INIT``) 1619 instead of in :c:func:`PyType_GenericAlloc`. Types that modify instance 1620 allocation or deallocation may need to be adjusted. 1621 (Contributed by Eddie Elizondo in :issue:`35810`.) 1622 1623* The new function :c:func:`PyCode_NewWithPosOnlyArgs` allows to create 1624 code objects like :c:func:`PyCode_New`, but with an extra *posonlyargcount* 1625 parameter for indicating the number of positional-only arguments. 1626 (Contributed by Pablo Galindo in :issue:`37221`.) 1627 1628* :c:func:`Py_SetPath` now sets :data:`sys.executable` to the program full 1629 path (:c:func:`Py_GetProgramFullPath`) rather than to the program name 1630 (:c:func:`Py_GetProgramName`). 1631 (Contributed by Victor Stinner in :issue:`38234`.) 1632 1633 1634Deprecated 1635========== 1636 1637* The distutils ``bdist_wininst`` command is now deprecated, use 1638 ``bdist_wheel`` (wheel packages) instead. 1639 (Contributed by Victor Stinner in :issue:`37481`.) 1640 1641* Deprecated methods ``getchildren()`` and ``getiterator()`` in 1642 the :mod:`~xml.etree.ElementTree` module now emit a 1643 :exc:`DeprecationWarning` instead of :exc:`PendingDeprecationWarning`. 1644 They will be removed in Python 3.9. 1645 (Contributed by Serhiy Storchaka in :issue:`29209`.) 1646 1647* Passing an object that is not an instance of 1648 :class:`concurrent.futures.ThreadPoolExecutor` to 1649 :meth:`loop.set_default_executor() <asyncio.loop.set_default_executor>` is 1650 deprecated and will be prohibited in Python 3.9. 1651 (Contributed by Elvis Pranskevichus in :issue:`34075`.) 1652 1653* The :meth:`__getitem__` methods of :class:`xml.dom.pulldom.DOMEventStream`, 1654 :class:`wsgiref.util.FileWrapper` and :class:`fileinput.FileInput` have been 1655 deprecated. 1656 1657 Implementations of these methods have been ignoring their *index* parameter, 1658 and returning the next item instead. 1659 (Contributed by Berker Peksag in :issue:`9372`.) 1660 1661* The :class:`typing.NamedTuple` class has deprecated the ``_field_types`` 1662 attribute in favor of the ``__annotations__`` attribute which has the same 1663 information. (Contributed by Raymond Hettinger in :issue:`36320`.) 1664 1665* :mod:`ast` classes ``Num``, ``Str``, ``Bytes``, ``NameConstant`` and 1666 ``Ellipsis`` are considered deprecated and will be removed in future Python 1667 versions. :class:`~ast.Constant` should be used instead. 1668 (Contributed by Serhiy Storchaka in :issue:`32892`.) 1669 1670* :class:`ast.NodeVisitor` methods ``visit_Num()``, ``visit_Str()``, 1671 ``visit_Bytes()``, ``visit_NameConstant()`` and ``visit_Ellipsis()`` are 1672 deprecated now and will not be called in future Python versions. 1673 Add the :meth:`~ast.NodeVisitor.visit_Constant` method to handle all 1674 constant nodes. 1675 (Contributed by Serhiy Storchaka in :issue:`36917`.) 1676 1677* The :func:`asyncio.coroutine` :term:`decorator` is deprecated and will be 1678 removed in version 3.10. Instead of ``@asyncio.coroutine``, use 1679 :keyword:`async def` instead. 1680 (Contributed by Andrew Svetlov in :issue:`36921`.) 1681 1682* In :mod:`asyncio`, the explicit passing of a *loop* argument has been 1683 deprecated and will be removed in version 3.10 for the following: 1684 :func:`asyncio.sleep`, :func:`asyncio.gather`, :func:`asyncio.shield`, 1685 :func:`asyncio.wait_for`, :func:`asyncio.wait`, :func:`asyncio.as_completed`, 1686 :class:`asyncio.Task`, :class:`asyncio.Lock`, :class:`asyncio.Event`, 1687 :class:`asyncio.Condition`, :class:`asyncio.Semaphore`, 1688 :class:`asyncio.BoundedSemaphore`, :class:`asyncio.Queue`, 1689 :func:`asyncio.create_subprocess_exec`, and 1690 :func:`asyncio.create_subprocess_shell`. 1691 1692* The explicit passing of coroutine objects to :func:`asyncio.wait` has been 1693 deprecated and will be removed in version 3.11. 1694 (Contributed by Yury Selivanov in :issue:`34790`.) 1695 1696* The following functions and methods are deprecated in the :mod:`gettext` 1697 module: :func:`~gettext.lgettext`, :func:`~gettext.ldgettext`, 1698 :func:`~gettext.lngettext` and :func:`~gettext.ldngettext`. 1699 They return encoded bytes, and it's possible that you will get unexpected 1700 Unicode-related exceptions if there are encoding problems with the 1701 translated strings. It's much better to use alternatives which return 1702 Unicode strings in Python 3. These functions have been broken for a long time. 1703 1704 Function :func:`~gettext.bind_textdomain_codeset`, methods 1705 :meth:`~gettext.NullTranslations.output_charset` and 1706 :meth:`~gettext.NullTranslations.set_output_charset`, and the *codeset* 1707 parameter of functions :func:`~gettext.translation` and 1708 :func:`~gettext.install` are also deprecated, since they are only used for 1709 the ``l*gettext()`` functions. 1710 (Contributed by Serhiy Storchaka in :issue:`33710`.) 1711 1712* The :meth:`~threading.Thread.isAlive()` method of :class:`threading.Thread` 1713 has been deprecated. 1714 (Contributed by Dong-hee Na in :issue:`35283`.) 1715 1716* Many builtin and extension functions that take integer arguments will 1717 now emit a deprecation warning for :class:`~decimal.Decimal`\ s, 1718 :class:`~fractions.Fraction`\ s and any other objects that can be converted 1719 to integers only with a loss (e.g. that have the :meth:`~object.__int__` 1720 method but do not have the :meth:`~object.__index__` method). In future 1721 version they will be errors. 1722 (Contributed by Serhiy Storchaka in :issue:`36048`.) 1723 1724* Deprecated passing the following arguments as keyword arguments: 1725 1726 - *func* in :func:`functools.partialmethod`, :func:`weakref.finalize`, 1727 :meth:`profile.Profile.runcall`, :meth:`cProfile.Profile.runcall`, 1728 :meth:`bdb.Bdb.runcall`, :meth:`trace.Trace.runfunc` and 1729 :func:`curses.wrapper`. 1730 - *function* in :meth:`unittest.TestCase.addCleanup`. 1731 - *fn* in the :meth:`~concurrent.futures.Executor.submit` method of 1732 :class:`concurrent.futures.ThreadPoolExecutor` and 1733 :class:`concurrent.futures.ProcessPoolExecutor`. 1734 - *callback* in :meth:`contextlib.ExitStack.callback`, 1735 :meth:`contextlib.AsyncExitStack.callback` and 1736 :meth:`contextlib.AsyncExitStack.push_async_callback`. 1737 - *c* and *typeid* in the :meth:`~multiprocessing.managers.Server.create` 1738 method of :class:`multiprocessing.managers.Server` and 1739 :class:`multiprocessing.managers.SharedMemoryServer`. 1740 - *obj* in :func:`weakref.finalize`. 1741 1742 In future releases of Python, they will be :ref:`positional-only 1743 <positional-only_parameter>`. 1744 (Contributed by Serhiy Storchaka in :issue:`36492`.) 1745 1746 1747API and Feature Removals 1748======================== 1749 1750The following features and APIs have been removed from Python 3.8: 1751 1752* Starting with Python 3.3, importing ABCs from :mod:`collections` was 1753 deprecated, and importing should be done from :mod:`collections.abc`. Being 1754 able to import from collections was marked for removal in 3.8, but has been 1755 delayed to 3.9. (See :issue:`36952`.) 1756 1757* The :mod:`macpath` module, deprecated in Python 3.7, has been removed. 1758 (Contributed by Victor Stinner in :issue:`35471`.) 1759 1760* The function :func:`platform.popen` has been removed, after having been 1761 deprecated since Python 3.3: use :func:`os.popen` instead. 1762 (Contributed by Victor Stinner in :issue:`35345`.) 1763 1764* The function :func:`time.clock` has been removed, after having been 1765 deprecated since Python 3.3: use :func:`time.perf_counter` or 1766 :func:`time.process_time` instead, depending 1767 on your requirements, to have well-defined behavior. 1768 (Contributed by Matthias Bussonnier in :issue:`36895`.) 1769 1770* The ``pyvenv`` script has been removed in favor of ``python3.8 -m venv`` 1771 to help eliminate confusion as to what Python interpreter the ``pyvenv`` 1772 script is tied to. (Contributed by Brett Cannon in :issue:`25427`.) 1773 1774* ``parse_qs``, ``parse_qsl``, and ``escape`` are removed from the :mod:`cgi` 1775 module. They are deprecated in Python 3.2 or older. They should be imported 1776 from the ``urllib.parse`` and ``html`` modules instead. 1777 1778* ``filemode`` function is removed from the :mod:`tarfile` module. 1779 It is not documented and deprecated since Python 3.3. 1780 1781* The :class:`~xml.etree.ElementTree.XMLParser` constructor no longer accepts 1782 the *html* argument. It never had an effect and was deprecated in Python 3.4. 1783 All other parameters are now :ref:`keyword-only <keyword-only_parameter>`. 1784 (Contributed by Serhiy Storchaka in :issue:`29209`.) 1785 1786* Removed the ``doctype()`` method of :class:`~xml.etree.ElementTree.XMLParser`. 1787 (Contributed by Serhiy Storchaka in :issue:`29209`.) 1788 1789* "unicode_internal" codec is removed. 1790 (Contributed by Inada Naoki in :issue:`36297`.) 1791 1792* The ``Cache`` and ``Statement`` objects of the :mod:`sqlite3` module are not 1793 exposed to the user. 1794 (Contributed by Aviv Palivoda in :issue:`30262`.) 1795 1796* The ``bufsize`` keyword argument of :func:`fileinput.input` and 1797 :func:`fileinput.FileInput` which was ignored and deprecated since Python 3.6 1798 has been removed. :issue:`36952` (Contributed by Matthias Bussonnier.) 1799 1800* The functions :func:`sys.set_coroutine_wrapper` and 1801 :func:`sys.get_coroutine_wrapper` deprecated in Python 3.7 have been removed; 1802 :issue:`36933` (Contributed by Matthias Bussonnier.) 1803 1804 1805Porting to Python 3.8 1806===================== 1807 1808This section lists previously described changes and other bugfixes 1809that may require changes to your code. 1810 1811 1812Changes in Python behavior 1813-------------------------- 1814 1815* Yield expressions (both ``yield`` and ``yield from`` clauses) are now disallowed 1816 in comprehensions and generator expressions (aside from the iterable expression 1817 in the leftmost :keyword:`!for` clause). 1818 (Contributed by Serhiy Storchaka in :issue:`10544`.) 1819 1820* The compiler now produces a :exc:`SyntaxWarning` when identity checks 1821 (``is`` and ``is not``) are used with certain types of literals 1822 (e.g. strings, numbers). These can often work by accident in CPython, 1823 but are not guaranteed by the language spec. The warning advises users 1824 to use equality tests (``==`` and ``!=``) instead. 1825 (Contributed by Serhiy Storchaka in :issue:`34850`.) 1826 1827* The CPython interpreter can swallow exceptions in some circumstances. 1828 In Python 3.8 this happens in fewer cases. In particular, exceptions 1829 raised when getting the attribute from the type dictionary are no longer 1830 ignored. (Contributed by Serhiy Storchaka in :issue:`35459`.) 1831 1832* Removed ``__str__`` implementations from builtin types :class:`bool`, 1833 :class:`int`, :class:`float`, :class:`complex` and few classes from 1834 the standard library. They now inherit ``__str__()`` from :class:`object`. 1835 As result, defining the ``__repr__()`` method in the subclass of these 1836 classes will affect their string representation. 1837 (Contributed by Serhiy Storchaka in :issue:`36793`.) 1838 1839* On AIX, :attr:`sys.platform` doesn't contain the major version anymore. 1840 It is always ``'aix'``, instead of ``'aix3'`` .. ``'aix7'``. Since 1841 older Python versions include the version number, so it is recommended to 1842 always use ``sys.platform.startswith('aix')``. 1843 (Contributed by M. Felt in :issue:`36588`.) 1844 1845* :c:func:`PyEval_AcquireLock` and :c:func:`PyEval_AcquireThread` now 1846 terminate the current thread if called while the interpreter is 1847 finalizing, making them consistent with :c:func:`PyEval_RestoreThread`, 1848 :c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`. If this 1849 behavior is not desired, guard the call by checking :c:func:`_Py_IsFinalizing` 1850 or :c:func:`sys.is_finalizing`. 1851 (Contributed by Joannah Nanjekye in :issue:`36475`.) 1852 1853 1854Changes in the Python API 1855------------------------- 1856 1857* The :func:`os.getcwdb` function now uses the UTF-8 encoding on Windows, 1858 rather than the ANSI code page: see :pep:`529` for the rationale. The 1859 function is no longer deprecated on Windows. 1860 (Contributed by Victor Stinner in :issue:`37412`.) 1861 1862* :class:`subprocess.Popen` can now use :func:`os.posix_spawn` in some cases 1863 for better performance. On Windows Subsystem for Linux and QEMU User 1864 Emulation, the :class:`Popen` constructor using :func:`os.posix_spawn` no longer raises an 1865 exception on errors like "missing program". Instead the child process fails with a 1866 non-zero :attr:`~Popen.returncode`. 1867 (Contributed by Joannah Nanjekye and Victor Stinner in :issue:`35537`.) 1868 1869* The *preexec_fn* argument of * :class:`subprocess.Popen` is no longer 1870 compatible with subinterpreters. The use of the parameter in a 1871 subinterpreter now raises :exc:`RuntimeError`. 1872 (Contributed by Eric Snow in :issue:`34651`, modified by Christian Heimes 1873 in :issue:`37951`.) 1874 1875* The :meth:`imap.IMAP4.logout` method no longer silently ignores arbitrary 1876 exceptions. 1877 (Contributed by Victor Stinner in :issue:`36348`.) 1878 1879* The function :func:`platform.popen` has been removed, after having been deprecated since 1880 Python 3.3: use :func:`os.popen` instead. 1881 (Contributed by Victor Stinner in :issue:`35345`.) 1882 1883* The :func:`statistics.mode` function no longer raises an exception 1884 when given multimodal data. Instead, it returns the first mode 1885 encountered in the input data. (Contributed by Raymond Hettinger 1886 in :issue:`35892`.) 1887 1888* The :meth:`~tkinter.ttk.Treeview.selection` method of the 1889 :class:`tkinter.ttk.Treeview` class no longer takes arguments. Using it with 1890 arguments for changing the selection was deprecated in Python 3.6. Use 1891 specialized methods like :meth:`~tkinter.ttk.Treeview.selection_set` for 1892 changing the selection. (Contributed by Serhiy Storchaka in :issue:`31508`.) 1893 1894* The :meth:`writexml`, :meth:`toxml` and :meth:`toprettyxml` methods of 1895 :mod:`xml.dom.minidom`, and the :meth:`write` method of :mod:`xml.etree`, 1896 now preserve the attribute order specified by the user. 1897 (Contributed by Diego Rojas and Raymond Hettinger in :issue:`34160`.) 1898 1899* A :mod:`dbm.dumb` database opened with flags ``'r'`` is now read-only. 1900 :func:`dbm.dumb.open` with flags ``'r'`` and ``'w'`` no longer creates 1901 a database if it does not exist. 1902 (Contributed by Serhiy Storchaka in :issue:`32749`.) 1903 1904* The ``doctype()`` method defined in a subclass of 1905 :class:`~xml.etree.ElementTree.XMLParser` will no longer be called and will 1906 emit a :exc:`RuntimeWarning` instead of a :exc:`DeprecationWarning`. 1907 Define the :meth:`doctype() <xml.etree.ElementTree.TreeBuilder.doctype>` 1908 method on a target for handling an XML doctype declaration. 1909 (Contributed by Serhiy Storchaka in :issue:`29209`.) 1910 1911* A :exc:`RuntimeError` is now raised when the custom metaclass doesn't 1912 provide the ``__classcell__`` entry in the namespace passed to 1913 ``type.__new__``. A :exc:`DeprecationWarning` was emitted in Python 1914 3.6--3.7. (Contributed by Serhiy Storchaka in :issue:`23722`.) 1915 1916* The :class:`cProfile.Profile` class can now be used as a context 1917 manager. (Contributed by Scott Sanderson in :issue:`29235`.) 1918 1919* :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`, 1920 :func:`shutil.copytree` and :func:`shutil.move` use platform-specific 1921 "fast-copy" syscalls (see 1922 :ref:`shutil-platform-dependent-efficient-copy-operations` section). 1923 1924* :func:`shutil.copyfile` default buffer size on Windows was changed from 1925 16 KiB to 1 MiB. 1926 1927* The ``PyGC_Head`` struct has changed completely. All code that touched the 1928 struct member should be rewritten. (See :issue:`33597`.) 1929 1930* The :c:type:`PyInterpreterState` struct has been moved into the "internal" 1931 header files (specifically Include/internal/pycore_pystate.h). An 1932 opaque ``PyInterpreterState`` is still available as part of the public 1933 API (and stable ABI). The docs indicate that none of the struct's 1934 fields are public, so we hope no one has been using them. However, 1935 if you do rely on one or more of those private fields and have no 1936 alternative then please open a BPO issue. We'll work on helping 1937 you adjust (possibly including adding accessor functions to the 1938 public API). (See :issue:`35886`.) 1939 1940* The :meth:`mmap.flush() <mmap.mmap.flush>` method now returns ``None`` on 1941 success and raises an exception on error under all platforms. Previously, 1942 its behavior was platform-dependent: a nonzero value was returned on success; 1943 zero was returned on error under Windows. A zero value was returned on 1944 success; an exception was raised on error under Unix. 1945 (Contributed by Berker Peksag in :issue:`2122`.) 1946 1947* :mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process 1948 external entities by default. 1949 (Contributed by Christian Heimes in :issue:`17239`.) 1950 1951* Deleting a key from a read-only :mod:`dbm` database (:mod:`dbm.dumb`, 1952 :mod:`dbm.gnu` or :mod:`dbm.ndbm`) raises :attr:`error` (:exc:`dbm.dumb.error`, 1953 :exc:`dbm.gnu.error` or :exc:`dbm.ndbm.error`) instead of :exc:`KeyError`. 1954 (Contributed by Xiang Zhang in :issue:`33106`.) 1955 1956* Simplified AST for literals. All constants will be represented as 1957 :class:`ast.Constant` instances. Instantiating old classes ``Num``, 1958 ``Str``, ``Bytes``, ``NameConstant`` and ``Ellipsis`` will return 1959 an instance of ``Constant``. 1960 (Contributed by Serhiy Storchaka in :issue:`32892`.) 1961 1962* :func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE` 1963 environment variable and does not use :envvar:`HOME`, which is not normally 1964 set for regular user accounts. 1965 (Contributed by Anthony Sottile in :issue:`36264`.) 1966 1967* The exception :class:`asyncio.CancelledError` now inherits from 1968 :class:`BaseException` rather than :class:`Exception` and no longer inherits 1969 from :class:`concurrent.futures.CancelledError`. 1970 (Contributed by Yury Selivanov in :issue:`32528`.) 1971 1972* The function :func:`asyncio.wait_for` now correctly waits for cancellation 1973 when using an instance of :class:`asyncio.Task`. Previously, upon reaching 1974 *timeout*, it was cancelled and immediately returned. 1975 (Contributed by Elvis Pranskevichus in :issue:`32751`.) 1976 1977* The function :func:`asyncio.BaseTransport.get_extra_info` now returns a safe 1978 to use socket object when 'socket' is passed to the *name* parameter. 1979 (Contributed by Yury Selivanov in :issue:`37027`.) 1980 1981* :class:`asyncio.BufferedProtocol` has graduated to the stable API. 1982 1983.. _bpo-36085-whatsnew: 1984 1985* DLL dependencies for extension modules and DLLs loaded with :mod:`ctypes` on 1986 Windows are now resolved more securely. Only the system paths, the directory 1987 containing the DLL or PYD file, and directories added with 1988 :func:`~os.add_dll_directory` are searched for load-time dependencies. 1989 Specifically, :envvar:`PATH` and the current working directory are no longer 1990 used, and modifications to these will no longer have any effect on normal DLL 1991 resolution. If your application relies on these mechanisms, you should check 1992 for :func:`~os.add_dll_directory` and if it exists, use it to add your DLLs 1993 directory while loading your library. Note that Windows 7 users will need to 1994 ensure that Windows Update KB2533623 has been installed (this is also verified 1995 by the installer). 1996 (Contributed by Steve Dower in :issue:`36085`.) 1997 1998* The header files and functions related to pgen have been removed after its 1999 replacement by a pure Python implementation. (Contributed by Pablo Galindo 2000 in :issue:`36623`.) 2001 2002* :class:`types.CodeType` has a new parameter in the second position of the 2003 constructor (*posonlyargcount*) to support positional-only arguments defined 2004 in :pep:`570`. The first argument (*argcount*) now represents the total 2005 number of positional arguments (including positional-only arguments). The new 2006 ``replace()`` method of :class:`types.CodeType` can be used to make the code 2007 future-proof. 2008 2009* The parameter ``digestmod`` for :func:`hmac.new` no longer uses the MD5 digest 2010 by default. 2011 2012Changes in the C API 2013-------------------- 2014 2015* The :c:struct:`PyCompilerFlags` structure got a new *cf_feature_version* 2016 field. It should be initialized to ``PY_MINOR_VERSION``. The field is ignored 2017 by default, and is used if and only if ``PyCF_ONLY_AST`` flag is set in 2018 *cf_flags*. 2019 (Contributed by Guido van Rossum in :issue:`35766`.) 2020 2021* The :c:func:`PyEval_ReInitThreads` function has been removed from the C API. 2022 It should not be called explicitly: use :c:func:`PyOS_AfterFork_Child` 2023 instead. 2024 (Contributed by Victor Stinner in :issue:`36728`.) 2025 2026* On Unix, C extensions are no longer linked to libpython except on Android 2027 and Cygwin. When Python is embedded, ``libpython`` must not be loaded with 2028 ``RTLD_LOCAL``, but ``RTLD_GLOBAL`` instead. Previously, using 2029 ``RTLD_LOCAL``, it was already not possible to load C extensions which 2030 were not linked to ``libpython``, like C extensions of the standard 2031 library built by the ``*shared*`` section of ``Modules/Setup``. 2032 (Contributed by Victor Stinner in :issue:`21536`.) 2033 2034* Use of ``#`` variants of formats in parsing or building value (e.g. 2035 :c:func:`PyArg_ParseTuple`, :c:func:`Py_BuildValue`, :c:func:`PyObject_CallFunction`, 2036 etc.) without ``PY_SSIZE_T_CLEAN`` defined raises ``DeprecationWarning`` now. 2037 It will be removed in 3.10 or 4.0. Read :ref:`arg-parsing` for detail. 2038 (Contributed by Inada Naoki in :issue:`36381`.) 2039 2040* Instances of heap-allocated types (such as those created with 2041 :c:func:`PyType_FromSpec`) hold a reference to their type object. 2042 Increasing the reference count of these type objects has been moved from 2043 :c:func:`PyType_GenericAlloc` to the more low-level functions, 2044 :c:func:`PyObject_Init` and :c:func:`PyObject_INIT`. 2045 This makes types created through :c:func:`PyType_FromSpec` behave like 2046 other classes in managed code. 2047 2048 :ref:`Statically allocated types <static-types>` are not affected. 2049 2050 For the vast majority of cases, there should be no side effect. 2051 However, types that manually increase the reference count after allocating 2052 an instance (perhaps to work around the bug) may now become immortal. 2053 To avoid this, these classes need to call Py_DECREF on the type object 2054 during instance deallocation. 2055 2056 To correctly port these types into 3.8, please apply the following 2057 changes: 2058 2059 * Remove :c:macro:`Py_INCREF` on the type object after allocating an 2060 instance - if any. 2061 This may happen after calling :c:func:`PyObject_New`, 2062 :c:func:`PyObject_NewVar`, :c:func:`PyObject_GC_New`, 2063 :c:func:`PyObject_GC_NewVar`, or any other custom allocator that uses 2064 :c:func:`PyObject_Init` or :c:func:`PyObject_INIT`. 2065 2066 Example: 2067 2068 .. code-block:: c 2069 2070 static foo_struct * 2071 foo_new(PyObject *type) { 2072 foo_struct *foo = PyObject_GC_New(foo_struct, (PyTypeObject *) type); 2073 if (foo == NULL) 2074 return NULL; 2075 #if PY_VERSION_HEX < 0x03080000 2076 // Workaround for Python issue 35810; no longer necessary in Python 3.8 2077 PY_INCREF(type) 2078 #endif 2079 return foo; 2080 } 2081 2082 * Ensure that all custom ``tp_dealloc`` functions of heap-allocated types 2083 decrease the type's reference count. 2084 2085 Example: 2086 2087 .. code-block:: c 2088 2089 static void 2090 foo_dealloc(foo_struct *instance) { 2091 PyObject *type = Py_TYPE(instance); 2092 PyObject_GC_Del(instance); 2093 #if PY_VERSION_HEX >= 0x03080000 2094 // This was not needed before Python 3.8 (Python issue 35810) 2095 Py_DECREF(type); 2096 #endif 2097 } 2098 2099 (Contributed by Eddie Elizondo in :issue:`35810`.) 2100 2101* The :c:macro:`Py_DEPRECATED()` macro has been implemented for MSVC. 2102 The macro now must be placed before the symbol name. 2103 2104 Example: 2105 2106 .. code-block:: c 2107 2108 Py_DEPRECATED(3.8) PyAPI_FUNC(int) Py_OldFunction(void); 2109 2110 (Contributed by Zackery Spytz in :issue:`33407`.) 2111 2112* The interpreter does not pretend to support binary compatibility of 2113 extension types across feature releases, anymore. A :c:type:`PyTypeObject` 2114 exported by a third-party extension module is supposed to have all the 2115 slots expected in the current Python version, including 2116 :c:member:`~PyTypeObject.tp_finalize` (:const:`Py_TPFLAGS_HAVE_FINALIZE` 2117 is not checked anymore before reading :c:member:`~PyTypeObject.tp_finalize`). 2118 2119 (Contributed by Antoine Pitrou in :issue:`32388`.) 2120 2121* The functions :c:func:`PyNode_AddChild` and :c:func:`PyParser_AddToken` now accept 2122 two additional ``int`` arguments *end_lineno* and *end_col_offset*. 2123 2124* The :file:`libpython38.a` file to allow MinGW tools to link directly against 2125 :file:`python38.dll` is no longer included in the regular Windows distribution. 2126 If you require this file, it may be generated with the ``gendef`` and 2127 ``dlltool`` tools, which are part of the MinGW binutils package: 2128 2129 .. code-block:: shell 2130 2131 gendef - python38.dll > tmp.def 2132 dlltool --dllname python38.dll --def tmp.def --output-lib libpython38.a 2133 2134 The location of an installed :file:`pythonXY.dll` will depend on the 2135 installation options and the version and language of Windows. See 2136 :ref:`using-on-windows` for more information. The resulting library should be 2137 placed in the same directory as :file:`pythonXY.lib`, which is generally the 2138 :file:`libs` directory under your Python installation. 2139 2140 (Contributed by Steve Dower in :issue:`37351`.) 2141 2142 2143CPython bytecode changes 2144------------------------ 2145 2146* The interpreter loop has been simplified by moving the logic of unrolling 2147 the stack of blocks into the compiler. The compiler emits now explicit 2148 instructions for adjusting the stack of values and calling the 2149 cleaning-up code for :keyword:`break`, :keyword:`continue` and 2150 :keyword:`return`. 2151 2152 Removed opcodes :opcode:`BREAK_LOOP`, :opcode:`CONTINUE_LOOP`, 2153 :opcode:`SETUP_LOOP` and :opcode:`SETUP_EXCEPT`. Added new opcodes 2154 :opcode:`ROT_FOUR`, :opcode:`BEGIN_FINALLY`, :opcode:`CALL_FINALLY` and 2155 :opcode:`POP_FINALLY`. Changed the behavior of :opcode:`END_FINALLY` 2156 and :opcode:`WITH_CLEANUP_START`. 2157 2158 (Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka in 2159 :issue:`17611`.) 2160 2161* Added new opcode :opcode:`END_ASYNC_FOR` for handling exceptions raised 2162 when awaiting a next item in an :keyword:`async for` loop. 2163 (Contributed by Serhiy Storchaka in :issue:`33041`.) 2164 2165* The :opcode:`MAP_ADD` now expects the value as the first element in the 2166 stack and the key as the second element. This change was made so the key 2167 is always evaluated before the value in dictionary comprehensions, as 2168 proposed by :pep:`572`. (Contributed by Jörn Heissler in :issue:`35224`.) 2169 2170 2171Demos and Tools 2172--------------- 2173 2174Added a benchmark script for timing various ways to access variables: 2175``Tools/scripts/var_access_benchmark.py``. 2176(Contributed by Raymond Hettinger in :issue:`35884`.) 2177 2178Here's a summary of performance improvements since Python 3.3: 2179 2180.. code-block:: none 2181 2182 Python version 3.3 3.4 3.5 3.6 3.7 3.8 2183 -------------- --- --- --- --- --- --- 2184 2185 Variable and attribute read access: 2186 read_local 4.0 7.1 7.1 5.4 5.1 3.9 2187 read_nonlocal 5.3 7.1 8.1 5.8 5.4 4.4 2188 read_global 13.3 15.5 19.0 14.3 13.6 7.6 2189 read_builtin 20.0 21.1 21.6 18.5 19.0 7.5 2190 read_classvar_from_class 20.5 25.6 26.5 20.7 19.5 18.4 2191 read_classvar_from_instance 18.5 22.8 23.5 18.8 17.1 16.4 2192 read_instancevar 26.8 32.4 33.1 28.0 26.3 25.4 2193 read_instancevar_slots 23.7 27.8 31.3 20.8 20.8 20.2 2194 read_namedtuple 68.5 73.8 57.5 45.0 46.8 18.4 2195 read_boundmethod 29.8 37.6 37.9 29.6 26.9 27.7 2196 2197 Variable and attribute write access: 2198 write_local 4.6 8.7 9.3 5.5 5.3 4.3 2199 write_nonlocal 7.3 10.5 11.1 5.6 5.5 4.7 2200 write_global 15.9 19.7 21.2 18.0 18.0 15.8 2201 write_classvar 81.9 92.9 96.0 104.6 102.1 39.2 2202 write_instancevar 36.4 44.6 45.8 40.0 38.9 35.5 2203 write_instancevar_slots 28.7 35.6 36.1 27.3 26.6 25.7 2204 2205 Data structure read access: 2206 read_list 19.2 24.2 24.5 20.8 20.8 19.0 2207 read_deque 19.9 24.7 25.5 20.2 20.6 19.8 2208 read_dict 19.7 24.3 25.7 22.3 23.0 21.0 2209 read_strdict 17.9 22.6 24.3 19.5 21.2 18.9 2210 2211 Data structure write access: 2212 write_list 21.2 27.1 28.5 22.5 21.6 20.0 2213 write_deque 23.8 28.7 30.1 22.7 21.8 23.5 2214 write_dict 25.9 31.4 33.3 29.3 29.2 24.7 2215 write_strdict 22.9 28.4 29.9 27.5 25.2 23.1 2216 2217 Stack (or queue) operations: 2218 list_append_pop 144.2 93.4 112.7 75.4 74.2 50.8 2219 deque_append_pop 30.4 43.5 57.0 49.4 49.2 42.5 2220 deque_append_popleft 30.8 43.7 57.3 49.7 49.7 42.8 2221 2222 Timing loop: 2223 loop_overhead 0.3 0.5 0.6 0.4 0.3 0.3 2224 2225The benchmarks were measured on an 2226`Intel® Core™ i7-4960HQ processor 2227<https://ark.intel.com/content/www/us/en/ark/products/76088/intel-core-i7-4960hq-processor-6m-cache-up-to-3-80-ghz.html>`_ 2228running the macOS 64-bit builds found at 2229`python.org <https://www.python.org/downloads/macos/>`_. 2230The benchmark script displays timings in nanoseconds. 2231 2232 2233Notable changes in Python 3.8.1 2234=============================== 2235 2236Due to significant security concerns, the *reuse_address* parameter of 2237:meth:`asyncio.loop.create_datagram_endpoint` is no longer supported. This is 2238because of the behavior of the socket option ``SO_REUSEADDR`` in UDP. For more 2239details, see the documentation for ``loop.create_datagram_endpoint()``. 2240(Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in 2241:issue:`37228`.) 2242 2243Notable changes in Python 3.8.8 2244=============================== 2245 2246Earlier Python versions allowed using both ``;`` and ``&`` as 2247query parameter separators in :func:`urllib.parse.parse_qs` and 2248:func:`urllib.parse.parse_qsl`. Due to security concerns, and to conform with 2249newer W3C recommendations, this has been changed to allow only a single 2250separator key, with ``&`` as the default. This change also affects 2251:func:`cgi.parse` and :func:`cgi.parse_multipart` as they use the affected 2252functions internally. For more details, please see their respective 2253documentation. 2254(Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in :issue:`42967`.) 2255 2256Notable changes in Python 3.8.12 2257================================ 2258 2259Starting with Python 3.8.12 the :mod:`ipaddress` module no longer accepts 2260any leading zeros in IPv4 address strings. Leading zeros are ambiguous and 2261interpreted as octal notation by some libraries. For example the legacy 2262function :func:`socket.inet_aton` treats leading zeros as octal notation. 2263glibc implementation of modern :func:`~socket.inet_pton` does not accept 2264any leading zeros. 2265 2266(Originally contributed by Christian Heimes in :issue:`36384`, and backported 2267to 3.8 by Achraf Merzouki.) 2268