1 ****************************
2 What's New In Python 3.8
3 ****************************
5 .. Rules for maintenance:
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.
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.
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.)
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
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.
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).
33 * Credit the author of a patch or bugfix. Just the name is
34 sufficient; the e-mail address isn't necessary.
36 * It's helpful to add the bug/patch number as a comment:
38 XXX Describe the transmogrify() function added to the socket
40 (Contributed by P.Y. Developer in :issue:`12345`.)
42 This saves the maintainer the effort of going through the Git log
43 when researching a change.
45 :Editor: Raymond Hettinger
47 This article explains the new features in Python 3.8, compared to 3.7.
48 For full details, see the :ref:`changelog <changelog>`.
50 Prerelease users should be aware that this document is currently in
51 draft form. It will be updated as Python 3.8 moves towards release, so
52 it's worth checking back even after reading earlier versions. Some
53 notable items not yet covered are:
55 * :pep:`578` - Runtime audit hooks for potentially sensitive operations
56 * ``python -m asyncio`` runs a natively async REPL
60 from datetime import date
61 from math import cos, radians
62 from unicodedata import normalize
67 Summary -- Release highlights
68 =============================
70 .. This section singles out the most important changes in Python 3.8.
74 .. PEP-sized items next.
81 Assignment expressions
82 ----------------------
84 There is new syntax ``:=`` that assigns values to variables as part of a larger
85 expression. It is affectionately known as "walrus operator" due to
86 its resemblance to `the eyes and tusks of a walrus
87 <https://en.wikipedia.org/wiki/Walrus#/media/File:Pacific_Walrus_-_Bull_(8247646168).jpg>`_.
89 In this example, the assignment expression helps avoid calling
92 if (n := len(a)) > 10:
93 print(f"List is too long ({n} elements, expected <= 10)")
95 A similar benefit arises during regular expression matching where
96 match objects are needed twice, once to test whether a match
97 occurred and another to extract a subgroup::
100 if (mo := re.search(r'(\d+)% discount', advertisement)):
101 discount = float(mo.group(1)) / 100.0
103 The operator is also useful with while-loops that compute
104 a value to test loop termination and then need that same
105 value again in the body of the loop::
107 # Loop over fixed length blocks
108 while (block := f.read(256)) != '':
111 Another motivating use case arises in list comprehensions where
112 a value computed in a filtering condition is also needed in
113 the expression body::
115 [clean_name.title() for name in names
116 if (clean_name := normalize('NFC', name)) in allowed_names]
118 Try to limit use of the walrus operator to clean cases that reduce
119 complexity and improve readability.
121 See :pep:`572` for a full description.
123 (Contributed by Emily Morehouse in :issue:`35224`.)
126 Positional-only parameters
127 --------------------------
129 There is a new function parameter syntax ``/`` to indicate that some
130 function parameters must be specified positionally and cannot be used as
131 keyword arguments. This is the same notation shown by ``help()`` for C
132 functions annotated with Larry Hastings' `Argument Clinic
133 <https://docs.python.org/3/howto/clinic.html>`_ tool.
135 In the following example, parameters *a* and *b* are positional-only,
136 while *c* or *d* can be positional or keyword, and *e* or *f* are
137 required to be keywords::
139 def f(a, b, /, c, d, *, e, f):
140 print(a, b, c, d, e, f)
142 The following is a valid call::
144 f(10, 20, 30, d=40, e=50, f=60)
146 However, these are invalid calls::
148 f(10, b=20, c=30, d=40, e=50, f=60) # b cannot be a keyword argument
149 f(10, 20, 30, 40, 50, f=60) # e must be a keyword argument
151 One use case for this notation is that it allows pure Python functions
152 to fully emulate behaviors of existing C coded functions. For example,
153 the built-in :func:`pow` function does not accept keyword arguments::
155 def pow(x, y, z=None, /):
156 "Emulate the built in pow() function"
158 return r if z is None else r%z
160 Another use case is to preclude keyword arguments when the parameter
161 name is not helpful. For example, the builtin :func:`len` function has
162 the signature ``len(obj, /)``. This precludes awkward calls such as::
164 len(obj='hello') # The "obj" keyword argument impairs readability
166 A further benefit of marking a parameter as positional-only is that it
167 allows the parameter name to be changed in the future without risk of
168 breaking client code. For example, in the :mod:`statistics` module, the
169 parameter name *dist* may be changed in the future. This was made
170 possible with the following function specification::
172 def quantiles(dist, /, *, n=4, method='exclusive')
175 Since the parameters to the left of ``/`` are not exposed as possible
176 keywords, the parameters names remain available for use in ``**kwargs``::
178 >>> def f(a, b, /, **kwargs):
179 ... print(a, b, kwargs)
181 >>> f(10, 20, a=1, b=2, c=3) # a and b are used in two ways
182 10 20 {'a': 1, 'b': 2, 'c': 3}
184 This greatly simplifies the implementation of functions and methods
185 that need to accept arbitrary keyword arguments. For example, here
186 is an except from code in the :mod:`collections` module::
190 def __init__(self, iterable=None, /, **kwds):
191 # Note "iterable" is a possible keyword argument
193 See :pep:`570` for a full description.
195 (Contributed by Pablo Galindo in :issue:`36540`.)
197 .. TODO: Pablo will sprint on docs at PyCon US 2019.
200 Parallel filesystem cache for compiled bytecode files
201 -----------------------------------------------------
203 The new :envvar:`PYTHONPYCACHEPREFIX` setting (also available as
204 :option:`-X` ``pycache_prefix``) configures the implicit bytecode
205 cache to use a separate parallel filesystem tree, rather than
206 the default ``__pycache__`` subdirectories within each source
209 The location of the cache is reported in :data:`sys.pycache_prefix`
210 (:const:`None` indicates the default location in ``__pycache__``
213 (Contributed by Carl Meyer in :issue:`33499`.)
215 Debug build uses the same ABI as release build
216 -----------------------------------------------
218 Python now uses the same ABI whether it built in release or debug mode. On
219 Unix, when Python is built in debug mode, it is now possible to load C
220 extensions built in release mode and C extensions built using the stable ABI.
222 Release builds and debug builds are now ABI compatible: defining the
223 ``Py_DEBUG`` macro no longer implies the ``Py_TRACE_REFS`` macro, which
224 introduces the only ABI incompatibility. The ``Py_TRACE_REFS`` macro, which
225 adds the :func:`sys.getobjects` function and the :envvar:`PYTHONDUMPREFS`
226 environment variable, can be set using the new ``./configure --with-trace-refs``
228 (Contributed by Victor Stinner in :issue:`36465`.)
230 On Unix, C extensions are no longer linked to libpython except on Android
233 for a statically linked Python to load a C extension built using a shared
235 (Contributed by Victor Stinner in :issue:`21536`.)
237 On Unix, when Python is built in debug mode, import now also looks for C
238 extensions compiled in release mode and for C extensions compiled with the
240 (Contributed by Victor Stinner in :issue:`36722`.)
242 To embed Python into an application, a new ``--embed`` option must be passed to
243 ``python3-config --libs --embed`` to get ``-lpython3.8`` (link the application
244 to libpython). To support both 3.8 and older, try ``python3-config --libs
245 --embed`` first and fallback to ``python3-config --libs`` (without ``--embed``)
246 if the previous command fails.
248 Add a pkg-config ``python-3.8-embed`` module to embed Python into an
249 application: ``pkg-config python-3.8-embed --libs`` includes ``-lpython3.8``.
250 To support both 3.8 and older, try ``pkg-config python-X.Y-embed --libs`` first
251 and fallback to ``pkg-config python-X.Y --libs`` (without ``--embed``) if the
252 previous command fails (replace ``X.Y`` with the Python version).
254 On the other hand, ``pkg-config python3.8 --libs`` no longer contains
255 ``-lpython3.8``. C extensions must not be linked to libpython (except on
256 Android and Cygwin, whose cases are handled by the script);
257 this change is backward incompatible on purpose.
258 (Contributed by Victor Stinner in :issue:`36721`.)
261 f-strings support ``=`` for self-documenting expressions and debugging
262 ----------------------------------------------------------------------
264 Added an ``=`` specifier to :term:`f-string`\s. An f-string such as
265 ``f'{expr=}'`` will expand to the text of the expression, an equal sign,
266 then the representation of the evaluated expression. For example:
268 >>> user = 'eric_idle'
269 >>> member_since = date(1975, 7, 31)
270 >>> f'{user=} {member_since=}'
271 "user='eric_idle' member_since=datetime.date(1975, 7, 31)"
273 The usual :ref:`f-string format specifiers <f-strings>` allow more
274 control over how the result of the expression is displayed::
276 >>> delta = date.today() - member_since
277 >>> f'{user=!s} {delta.days=:,d}'
278 'user=eric_idle delta.days=16,075'
280 The ``=`` specifier will display the whole expression so that
281 calculations can be shown::
283 >>> print(f'{theta=} {cos(radians(theta))=:.3f}')
284 theta=30 cos(radians(theta))=0.866
286 (Contributed by Eric V. Smith and Larry Hastings in :issue:`36817`.)
288 PEP 587: Python Initialization Configuration
289 --------------------------------------------
291 The :pep:`587` adds a new C API to configure the Python Initialization
292 providing finer control on the whole configuration and better error reporting.
297 * :c:type:`PyPreConfig`
299 * :c:type:`PyWideStringList`
303 * :c:func:`PyConfig_Clear`
304 * :c:func:`PyConfig_InitIsolatedConfig`
305 * :c:func:`PyConfig_InitPythonConfig`
306 * :c:func:`PyConfig_Read`
307 * :c:func:`PyConfig_SetArgv`
308 * :c:func:`PyConfig_SetBytesArgv`
309 * :c:func:`PyConfig_SetBytesString`
310 * :c:func:`PyConfig_SetString`
311 * :c:func:`PyPreConfig_InitIsolatedConfig`
312 * :c:func:`PyPreConfig_InitPythonConfig`
313 * :c:func:`PyStatus_Error`
314 * :c:func:`PyStatus_Exception`
315 * :c:func:`PyStatus_Exit`
316 * :c:func:`PyStatus_IsError`
317 * :c:func:`PyStatus_IsExit`
318 * :c:func:`PyStatus_NoMemory`
319 * :c:func:`PyStatus_Ok`
320 * :c:func:`PyWideStringList_Append`
321 * :c:func:`PyWideStringList_Insert`
322 * :c:func:`Py_BytesMain`
323 * :c:func:`Py_ExitStatusException`
324 * :c:func:`Py_InitializeFromConfig`
325 * :c:func:`Py_PreInitialize`
326 * :c:func:`Py_PreInitializeFromArgs`
327 * :c:func:`Py_PreInitializeFromBytesArgs`
328 * :c:func:`Py_RunMain`
330 This PEP also adds ``_PyRuntimeState.preconfig`` (:c:type:`PyPreConfig` type)
331 and ``PyInterpreterState.config`` (:c:type:`PyConfig` type) fields to these
332 internal structures. ``PyInterpreterState.config`` becomes the new
333 reference configuration, replacing global configuration variables and
334 other private variables.
336 See :ref:`Python Initialization Configuration <init-config>` for the
339 See :pep:`587` for a full description.
341 (Contributed by Victor Stinner in :issue:`36763`.)
344 Vectorcall: a fast calling protocol for CPython
345 -----------------------------------------------
347 The "vectorcall" protocol is added to the Python/C API.
348 It is meant to formalize existing optimizations which were already done
350 Any extension type implementing a callable can use this protocol.
352 This is currently provisional,
353 the aim is to make it fully public in Python 3.9.
355 See :pep:`590` for a full description.
357 (Contributed by Jeroen Demeyer and Mark Shannon in :issue:`36974`.)
360 Pickle protocol 5 with out-of-band data buffers
361 -----------------------------------------------
363 When :mod:`pickle` is used to transfer large data between Python processes
364 in order to take advantage of multi-core or multi-machine processing,
365 it is important to optimize the transfer by reducing memory copies, and
366 possibly by applying custom techniques such as data-dependent compression.
368 The :mod:`pickle` protocol 5 introduces support for out-of-band buffers
369 where :pep:`3118`-compatible data can be transmitted separately from the
370 main pickle stream, at the discretion of the communication layer.
372 See :pep:`574` for a full description.
374 (Contributed by Antoine Pitrou in :issue:`36785`.)
377 Other Language Changes
378 ======================
380 * A :keyword:`continue` statement was illegal in the :keyword:`finally` clause
381 due to a problem with the implementation. In Python 3.8 this restriction
383 (Contributed by Serhiy Storchaka in :issue:`32489`.)
385 * The :class:`bool`, :class:`int`, and :class:`fractions.Fraction` types
386 now have an :meth:`~int.as_integer_ratio` method like that found in
387 :class:`float` and :class:`decimal.Decimal`. This minor API extension
388 makes it possible to write ``numerator, denominator =
389 x.as_integer_ratio()`` and have it work across multiple numeric types.
390 (Contributed by Lisa Roach in :issue:`33073` and Raymond Hettinger in
393 * Constructors of :class:`int`, :class:`float` and :class:`complex` will now
394 use the :meth:`~object.__index__` special method, if available and the
395 corresponding method :meth:`~object.__int__`, :meth:`~object.__float__`
396 or :meth:`~object.__complex__` is not available.
397 (Contributed by Serhiy Storchaka in :issue:`20092`.)
399 * Added support of ``\N{name}`` escapes in :mod:`regular expressions <re>`::
401 >>> notice = 'Copyright © 2019'
402 >>> copyright_year_pattern = re.compile(r'\N{copyright sign}\s*(\d{4})')
403 >>> int(copyright_year_pattern.search(notice).group(1))
406 (Contributed by Jonathan Eunice and Serhiy Storchaka in :issue:`30688`.)
408 * Dict and dictviews are now iterable in reversed insertion order using
409 :func:`reversed`. (Contributed by Rémi Lapeyre in :issue:`33462`.)
411 * The syntax allowed for keyword names in function calls was further
412 restricted. In particular, ``f((keyword)=arg)`` is no longer allowed. It was
413 never intended to permit more than a bare name on the left-hand side of a
414 keyword argument assignment term. See :issue:`34641`.
416 * Generalized iterable unpacking in :keyword:`yield` and
417 :keyword:`return` statements no longer requires enclosing parentheses.
418 This brings the *yield* and *return* syntax into better agreement with
419 normal assignment syntax::
421 >>> def parse(family):
422 lastname, *members = family.split()
423 return lastname.upper(), *members
425 >>> parse('simpsons homer marge bart lisa sally')
426 ('SIMPSONS', 'homer', 'marge', 'bart', 'lisa', 'sally')
429 (Contributed by David Cuthbert and Jordan Chapman in :issue:`32117`.)
431 * When a comma is missed in code such as ``[(10, 20) (30, 40)]``, the
432 compiler displays a :exc:`SyntaxWarning` with a helpful suggestion.
433 This improves on just having a :exc:`TypeError` indicating that the
434 first tuple was not callable. (Contributed by Serhiy Storchaka in
437 * Arithmetic operations between subclasses of :class:`datetime.date` or
438 :class:`datetime.datetime` and :class:`datetime.timedelta` objects now return
439 an instance of the subclass, rather than the base class. This also affects
440 the return type of operations whose implementation (directly or indirectly)
441 uses :class:`datetime.timedelta` arithmetic, such as
442 :meth:`datetime.datetime.astimezone`.
443 (Contributed by Paul Ganssle in :issue:`32417`.)
445 * When the Python interpreter is interrupted by Ctrl-C (SIGINT) and the
446 resulting :exc:`KeyboardInterrupt` exception is not caught, the Python process
447 now exits via a SIGINT signal or with the correct exit code such that the
448 calling process can detect that it died due to a Ctrl-C. Shells on POSIX
449 and Windows use this to properly terminate scripts in interactive sessions.
450 (Contributed by Google via Gregory P. Smith in :issue:`1054041`.)
452 * Some advanced styles of programming require updating the
453 :class:`types.CodeType` object for an existing function. Since code
454 objects are immutable, a new code object needs to be created, one
455 that is modeled on the existing code object. With 19 parameters,
456 this was somewhat tedious. Now, the new ``replace()`` method makes
457 it possible to create a clone with a few altered parameters.
459 Here's an example that alters the :func:`statistics.mean` function to
460 prevent the *data* parameter from being used as a keyword argument::
462 >>> from statistics import mean
463 >>> mean(data=[10, 20, 90])
465 >>> mean.__code__ = mean.__code__.replace(co_posonlyargcount=1)
466 >>> mean(data=[10, 20, 90])
467 Traceback (most recent call last):
469 TypeError: mean() got some positional-only arguments passed as keyword arguments: 'data'
471 (Contributed by Victor Stinner in :issue:`37032`.)
473 * For integers, the three-argument form of the :func:`pow` function now
474 permits the exponent to be negative in the case where the base is
475 relatively prime to the modulus. It then computes a modular inverse to
476 the base when the exponent is ``-1``, and a suitable power of that
477 inverse for other negative exponents. For example, to compute the
478 `modular multiplicative inverse
479 <https://en.wikipedia.org/wiki/Modular_multiplicative_inverse>`_ of 38
487 Modular inverses arise in the solution of `linear Diophantine
488 equations <https://en.wikipedia.org/wiki/Diophantine_equation>`_.
489 For example, to find integer solutions for ``4258𝑥 + 147𝑦 = 369``,
490 first rewrite as ``4258𝑥 ≡ 369 (mod 147)`` then solve:
492 >>> x = 369 * pow(4258, -1, 147) % 147
493 >>> y = (4258 * x - 369) // -147
494 >>> 4258 * x + 147 * y
497 (Contributed by Mark Dickinson in :issue:`36027`.)
499 * Dict comprehensions have been synced-up with dict literals so that the
500 key is computed first and the value second::
502 >>> # Dict comprehension
503 >>> cast = {input('role? '): input('actor? ') for i in range(2)}
510 >>> cast = {input('role? '): input('actor? ')}
514 The guaranteed execution order is helpful with assignment expressions
515 because variables assigned in the key expression will be available in
516 the value expression::
518 >>> names = ['Martin von Löwis', 'Łukasz Langa', 'Walter Dörwald']
519 >>> {(n := normalize('NFC', name)).casefold() : n for name in names}
520 {'martin von löwis': 'Martin von Löwis',
521 'łukasz langa': 'Łukasz Langa',
522 'walter dörwald': 'Walter Dörwald'}
528 * The new :mod:`importlib.metadata` module provides (provisional) support for
529 reading metadata from third-party packages. For example, it can extract an
530 installed package's version number, list of entry points, and more::
532 >>> # Note following example requires that the popular "requests"
533 >>> # package has been installed.
535 >>> from importlib.metadata import version, requires, files
536 >>> version('requests')
538 >>> list(requires('requests'))
539 ['chardet (<3.1.0,>=3.0.2)']
540 >>> list(files('requests'))[:5]
541 [PackagePath('requests-2.22.0.dist-info/INSTALLER'),
542 PackagePath('requests-2.22.0.dist-info/LICENSE'),
543 PackagePath('requests-2.22.0.dist-info/METADATA'),
544 PackagePath('requests-2.22.0.dist-info/RECORD'),
545 PackagePath('requests-2.22.0.dist-info/WHEEL')]
547 (Contributed in :issue:`34632` by Barry Warsaw and Jason R. Coombs.)
557 AST nodes now have ``end_lineno`` and ``end_col_offset`` attributes,
558 which give the precise location of the end of the node. (This only
559 applies to nodes that have ``lineno`` and ``col_offset`` attributes.)
561 The :func:`ast.parse` function has some new flags:
563 * ``type_comments=True`` causes it to return the text of :pep:`484` and
564 :pep:`526` type comments associated with certain AST nodes;
566 * ``mode='func_type'`` can be used to parse :pep:`484` "signature type
567 comments" (returned for function definition AST nodes);
569 * ``feature_version=(3, N)`` allows specifying an earlier Python 3
570 version. (For example, ``feature_version=(3, 4)`` will treat
571 ``async`` and ``await`` as non-reserved words.)
573 New function :func:`ast.get_source_segment` returns the source code
574 for a specific AST node.
580 On Windows, the default event loop is now :class:`~asyncio.ProactorEventLoop`.
581 (Contributed by Victor Stinner in :issue:`34687`.)
583 :class:`~asyncio.ProactorEventLoop` now also supports UDP.
584 (Contributed by Adam Meily and Andrew Svetlov in :issue:`29883`.)
586 :class:`~asyncio.ProactorEventLoop` can now be interrupted by
587 :exc:`KeyboardInterrupt` ("CTRL+C").
588 (Contributed by Vladimir Matveev in :issue:`23057`.)
594 The :func:`compile` built-in has been improved to accept the
595 ``ast.PyCF_ALLOW_TOP_LEVEL_AWAIT`` flag. With this new flag passed,
596 :func:`compile` will allow top-level ``await``, ``async for`` and ``async with``
597 constructs that are usually considered invalid syntax. Asynchronous code object
598 marked with the ``CO_COROUTINE`` flag may then be returned.
600 (Contributed by Matthias Bussonnier in :issue:`34616`)
605 The :meth:`_asdict()` method for :func:`collections.namedtuple` now returns
606 a :class:`dict` instead of a :class:`collections.OrderedDict`. This works because
607 regular dicts have guaranteed ordering since Python 3.7. If the extra
608 features of :class:`OrderedDict` are required, the suggested remediation is
609 to cast the result to the desired type: ``OrderedDict(nt._asdict())``.
610 (Contributed by Raymond Hettinger in :issue:`35864`.)
616 On Windows, :class:`~ctypes.CDLL` and subclasses now accept a *winmode* parameter
617 to specify flags for the underlying ``LoadLibraryEx`` call. The default flags are
618 set to only load DLL dependencies from trusted locations, including the path
619 where the DLL is stored (if a full or partial path is used to load the initial
620 DLL) and paths added by :func:`~os.add_dll_directory`.
626 :func:`functools.lru_cache` can now be used as a straight decorator rather
627 than as a function returning a decorator. So both of these are now supported::
633 @lru_cache(maxsize=256)
637 (Contributed by Raymond Hettinger in :issue:`36772`.)
643 Added new alternate constructors :meth:`datetime.date.fromisocalendar` and
644 :meth:`datetime.datetime.fromisocalendar`, which construct :class:`date` and
645 :class:`datetime` objects respectively from ISO year, week number and weekday;
646 these are the inverse of each class's ``isocalendar`` method.
647 (Contributed by Paul Ganssle in :issue:`36004`.)
653 Added :func:`~gettext.pgettext` and its variants.
654 (Contributed by Franz Glasner, Éric Araujo, and Cheryl Sabella in :issue:`2504`.)
660 Output over N lines (50 by default) is squeezed down to a button.
661 N can be changed in the PyShell section of the General page of the
662 Settings dialog. Fewer, but possibly extra long, lines can be squeezed by
663 right clicking on the output. Squeezed output can be expanded in place
664 by double-clicking the button or into the clipboard or a separate window
665 by right-clicking the button. (Contributed by Tal Einat in :issue:`1529353`.)
667 Add "Run Customized" to the Run menu to run a module with customized
668 settings. Any command line arguments entered are added to sys.argv.
669 They also re-appear in the box for the next customized run. One can also
670 suppress the normal Shell main module restart. (Contributed by Cheryl
671 Sabella, Terry Jan Reedy, and others in :issue:`5680` and :issue:`37627`.)
673 Add optional line numbers for IDLE editor windows. Windows
674 open without line numbers unless set otherwise in the General
675 tab of the configuration dialog. Line numbers for an existing
676 window are shown and hidden in the Options menu.
677 (Contributed by Tal Einat and Saimadhav Heblikar in :issue:`17535`.)
679 The changes above have been backported to 3.7 maintenance releases.
685 The :func:`inspect.getdoc` function can now find docstrings for ``__slots__``
686 if that attribute is a :class:`dict` where the values are docstrings.
687 This provides documentation options similar to what we already have
688 for :func:`property`, :func:`classmethod`, and :func:`staticmethod`::
691 __slots__ = {'bit_rate': 'expressed in kilohertz to one decimal place',
692 'duration': 'in seconds, rounded up to an integer'}
693 def __init__(self, bit_rate, duration):
694 self.bit_rate = round(bit_rate / 1000.0, 1)
695 self.duration = ceil(duration)
701 In development mode (:option:`-X` ``env``) and in debug build, the
702 :class:`io.IOBase` finalizer now logs the exception if the ``close()`` method
703 fails. The exception is ignored silently by default in release build.
704 (Contributed by Victor Stinner in :issue:`18748`.)
710 :func:`~gc.get_objects` can now receive an optional *generation* parameter
711 indicating a generation to get objects from. Contributed in
712 :issue:`36016` by Pablo Galindo.
718 Added the *mtime* parameter to :func:`gzip.compress` for reproducible output.
719 (Contributed by Guo Ci Teo in :issue:`34898`.)
721 A :exc:`~gzip.BadGzipFile` exception is now raised instead of :exc:`OSError`
722 for certain types of invalid or corrupt gzip files.
723 (Contributed by Filip Gruszczyński, Michele Orrù, and Zackery Spytz in
730 Add optional line numbers for IDLE editor windows. Windows
731 open without line numbers unless set otherwise in the General
732 tab of the configuration dialog.
733 (Contributed by Tal Einat and Saimadhav Heblikar in :issue:`17535`.)
735 Output over N lines (50 by default) is squeezed down to a button.
736 N can be changed in the PyShell section of the General page of the
737 Settings dialog. Fewer, but possibly extra long, lines can be squeezed by
738 right clicking on the output. Squeezed output can be expanded in place
739 by double-clicking the button or into the clipboard or a separate window
740 by right-clicking the button. (Contributed by Tal Einat in :issue:`1529353`.)
742 The changes above have been backported to 3.7 maintenance releases.
748 Add option ``--json-lines`` to parse every input line as separate JSON object.
749 (Contributed by Weipeng Hong in :issue:`31553`.)
755 Added new function :func:`math.dist` for computing Euclidean distance
756 between two points. (Contributed by Raymond Hettinger in :issue:`33089`.)
758 Expanded the :func:`math.hypot` function to handle multiple dimensions.
759 Formerly, it only supported the 2-D case.
760 (Contributed by Raymond Hettinger in :issue:`33089`.)
762 Added new function, :func:`math.prod`, as analogous function to :func:`sum`
763 that returns the product of a 'start' value (default: 1) times an iterable of
767 >>> likelihoods = [0.625, 0.84, 0.30]
768 >>> math.prod(likelihoods, start=prior)
771 (Contributed by Pablo Galindo in :issue:`35606`)
773 Added new function :func:`math.isqrt` for computing integer square roots.
774 (Contributed by Mark Dickinson in :issue:`36887`.)
776 The function :func:`math.factorial` no longer accepts arguments that are not
777 int-like. (Contributed by Pablo Galindo in :issue:`33083`.)
783 The :class:`mmap.mmap` class now has an :meth:`~mmap.mmap.madvise` method to
784 access the ``madvise()`` system call.
785 (Contributed by Zackery Spytz in :issue:`32941`.)
791 Added new :mod:`multiprocessing.shared_memory` module.
792 (Contributed Davin Potts in :issue:`35813`.)
794 On macOS, the *spawn* start method is now used by default.
795 (Contributed by Victor Stinner in :issue:`33725`.)
801 Added new function :func:`~os.add_dll_directory` on Windows for providing
802 additional search paths for native dependencies when importing extension
803 modules or loading DLLs using :mod:`ctypes`.
805 A new :func:`os.memfd_create` function was added to wrap the
806 ``memfd_create()`` syscall.
807 (Contributed by Zackery Spytz and Christian Heimes in :issue:`26836`.)
809 On Windows, much of the manual logic for handling reparse points (including
810 symlinks and directory junctions) has been delegated to the operating system.
811 Specifically, :func:`os.stat` will now traverse anything supported by the
812 operating system, while :func:`os.lstat` will only open reparse points that
813 identify as "name surrogates" while others are opened as for :func:`os.stat`.
814 In all cases, :attr:`stat_result.st_mode` will only have ``S_IFLNK`` set for
815 symbolic links and not other kinds of reparse points. To identify other kinds
816 of reparse point, check the new :attr:`stat_result.st_reparse_tag` attribute.
818 On Windows, :func:`os.readlink` is now able to read directory junctions. Note
819 that :func:`~os.path.islink` will return ``False`` for directory junctions,
820 and so code that checks ``islink`` first will continue to treat junctions as
821 directories, while code that handles errors from :func:`os.readlink` may now
822 treat junctions as links.
828 :mod:`os.path` functions that return a boolean result like
829 :func:`~os.path.exists`, :func:`~os.path.lexists`, :func:`~os.path.isdir`,
830 :func:`~os.path.isfile`, :func:`~os.path.islink`, and :func:`~os.path.ismount`
831 now return ``False`` instead of raising :exc:`ValueError` or its subclasses
832 :exc:`UnicodeEncodeError` and :exc:`UnicodeDecodeError` for paths that contain
833 characters or bytes unrepresentable at the OS level.
834 (Contributed by Serhiy Storchaka in :issue:`33721`.)
836 :func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE`
837 environment variable and does not use :envvar:`HOME`, which is not normally set
838 for regular user accounts.
840 :func:`~os.path.isdir` on Windows no longer returns true for a link to a
841 non-existent directory.
843 :func:`~os.path.realpath` on Windows now resolves reparse points, including
844 symlinks and directory junctions.
850 Added a new variable holding structured version information for the
851 underlying ncurses library: :data:`~curses.ncurses_version`.
852 (Contributed by Serhiy Storchaka in :issue:`31680`.)
858 :mod:`pathlib.Path` methods that return a boolean result like
859 :meth:`~pathlib.Path.exists()`, :meth:`~pathlib.Path.is_dir()`,
860 :meth:`~pathlib.Path.is_file()`, :meth:`~pathlib.Path.is_mount()`,
861 :meth:`~pathlib.Path.is_symlink()`, :meth:`~pathlib.Path.is_block_device()`,
862 :meth:`~pathlib.Path.is_char_device()`, :meth:`~pathlib.Path.is_fifo()`,
863 :meth:`~pathlib.Path.is_socket()` now return ``False`` instead of raising
864 :exc:`ValueError` or its subclass :exc:`UnicodeEncodeError` for paths that
865 contain characters unrepresentable at the OS level.
866 (Contributed by Serhiy Storchaka in :issue:`33721`.)
868 Added :meth:`pathlib.Path.link_to()` which creates a hard link pointing
870 (Contributed by Joannah Nanjekye in :issue:`26978`)
876 Reduction methods can now include a 6th item in the tuple they return. This
877 item should specify a custom state-setting method that's called instead of the
878 regular ``__setstate__`` method.
879 (Contributed by Pierre Glaser and Olivier Grisel in :issue:`35900`)
881 :mod:`pickle` extensions subclassing the C-optimized :class:`~pickle.Pickler`
882 can now override the pickling logic of functions and classes by defining the
883 special :meth:`~pickle.Pickler.reducer_override` method.
884 (Contributed by Pierre Glaser and Olivier Grisel in :issue:`35900`)
890 Added new :class:`plistlib.UID` and enabled support for reading and writing
891 NSKeyedArchiver-encoded binary plists.
892 (Contributed by Jon Janzen in :issue:`26707`.)
898 :func:`py_compile.compile` now supports silent mode.
899 (Contributed by Joannah Nanjekye in :issue:`22640`.)
905 Added :meth:`~socket.create_server()` and :meth:`~socket.has_dualstack_ipv6()`
906 convenience functions to automate the necessary tasks usually involved when
907 creating a server socket, including accepting both IPv4 and IPv6 connections
908 on the same socket. (Contributed by Giampaolo Rodola in :issue:`17561`.)
910 The :func:`socket.if_nameindex()`, :func:`socket.if_nametoindex()`, and
911 :func:`socket.if_indextoname()` functions have been implemented on Windows.
912 (Contributed by Zackery Spytz in :issue:`37007`.)
917 The new :func:`shlex.join` function acts as the inverse of :func:`shlex.split`.
918 (Contributed by Bo Bayles in :issue:`32102`.)
923 :func:`shutil.copytree` now accepts a new ``dirs_exist_ok`` keyword argument.
924 (Contributed by Josh Bronson in :issue:`20849`.)
926 :func:`shutil.make_archive` now defaults to the modern pax (POSIX.1-2001)
927 format for new archives to improve portability and standards conformance,
928 inherited from the corresponding change to the :mod:`tarfile` module.
929 (Contributed by C.A.M. Gerlach in :issue:`30661`.)
931 :func:`shutil.rmtree` on Windows now removes directory junctions without
932 recursively removing their contents first.
938 Added :attr:`SSLContext.post_handshake_auth` to enable and
939 :meth:`ssl.SSLSocket.verify_client_post_handshake` to initiate TLS 1.3
940 post-handshake authentication.
941 (Contributed by Christian Heimes in :issue:`34670`.)
947 Added :func:`statistics.fmean` as a faster, floating point variant of
948 :func:`statistics.mean()`. (Contributed by Raymond Hettinger and
949 Steven D'Aprano in :issue:`35904`.)
951 Added :func:`statistics.geometric_mean()`
952 (Contributed by Raymond Hettinger in :issue:`27181`.)
954 Added :func:`statistics.multimode` that returns a list of the most
955 common values. (Contributed by Raymond Hettinger in :issue:`35892`.)
957 Added :func:`statistics.quantiles` that divides data or a distribution
958 in to equiprobable intervals (e.g. quartiles, deciles, or percentiles).
959 (Contributed by Raymond Hettinger in :issue:`36546`.)
961 Added :class:`statistics.NormalDist`, a tool for creating
962 and manipulating normal distributions of a random variable.
963 (Contributed by Raymond Hettinger in :issue:`36018`.)
967 >>> temperature_feb = NormalDist.from_samples([4, 12, -3, 2, 7, 14])
968 >>> temperature_feb.mean
970 >>> temperature_feb.stdev
973 >>> temperature_feb.cdf(3) # Chance of being under 3 degrees
975 >>> # Relative chance of being 7 degrees versus 10 degrees
976 >>> temperature_feb.pdf(7) / temperature_feb.pdf(10)
979 >>> el_niño = NormalDist(4, 2.5)
980 >>> temperature_feb += el_niño # Add in a climate effect
982 NormalDist(mu=10.0, sigma=6.830080526611674)
984 >>> temperature_feb * (9/5) + 32 # Convert to Fahrenheit
985 NormalDist(mu=50.0, sigma=12.294144947901014)
986 >>> temperature_feb.samples(3) # Generate random samples
987 [7.672102882379219, 12.000027119750287, 4.647488369766392]
993 Add new :func:`sys.unraisablehook` function which can be overridden to control
994 how "unraisable exceptions" are handled. It is called when an exception has
995 occurred but there is no way for Python to handle it. For example, when a
996 destructor raises an exception or during garbage collection
997 (:func:`gc.collect`).
998 (Contributed by Victor Stinner in :issue:`36829`.)
1004 The :mod:`tarfile` module now defaults to the modern pax (POSIX.1-2001)
1005 format for new archives, instead of the previous GNU-specific one.
1006 This improves cross-platform portability with a consistent encoding (UTF-8)
1007 in a standardized and extensible format, and offers several other benefits.
1008 (Contributed by C.A.M. Gerlach in :issue:`36268`.)
1014 * Add a new :func:`threading.excepthook` function which handles uncaught
1015 :meth:`threading.Thread.run` exception. It can be overridden to control how
1016 uncaught :meth:`threading.Thread.run` exceptions are handled.
1017 (Contributed by Victor Stinner in :issue:`1230540`.)
1020 :func:`threading.get_native_id` function and a :data:`~threading.Thread.native_id`
1021 attribute to the :class:`threading.Thread` class. These return the native
1022 integral Thread ID of the current thread assigned by the kernel.
1023 This feature is only available on certain platforms, see
1024 :func:`get_native_id <threading.get_native_id>` for more information.
1025 (Contributed by Jake Tesler in :issue:`36084`.)
1031 The :mod:`tokenize` module now implicitly emits a ``NEWLINE`` token when
1032 provided with input that does not have a trailing new line. This behavior
1033 now matches what the C tokenizer does internally.
1034 (Contributed by Ammar Askar in :issue:`33899`.)
1039 Added methods :meth:`~tkinter.Spinbox.selection_from`,
1040 :meth:`~tkinter.Spinbox.selection_present`,
1041 :meth:`~tkinter.Spinbox.selection_range` and
1042 :meth:`~tkinter.Spinbox.selection_to`
1043 in the :class:`tkinter.Spinbox` class.
1044 (Contributed by Juliette Monsel in :issue:`34829`.)
1046 Added method :meth:`~tkinter.Canvas.moveto`
1047 in the :class:`tkinter.Canvas` class.
1048 (Contributed by Juliette Monsel in :issue:`23831`.)
1050 The :class:`tkinter.PhotoImage` class now has
1051 :meth:`~tkinter.PhotoImage.transparency_get` and
1052 :meth:`~tkinter.PhotoImage.transparency_set` methods. (Contributed by
1053 Zackery Spytz in :issue:`25451`.)
1058 Added new clock :data:`~time.CLOCK_UPTIME_RAW` for macOS 10.12.
1059 (Contributed by Joannah Nanjekye in :issue:`35702`.)
1065 The :mod:`typing` module incorporates several new features:
1067 * Protocol definitions. See :pep:`544`, :class:`typing.Protocol` and
1068 :func:`typing.runtime_checkable`. Simple ABCs like
1069 :class:`typing.SupportsInt` are now ``Protocol`` subclasses.
1071 * A dictionary type with per-key types. See :pep:`589` and
1072 :class:`typing.TypedDict`.
1074 * Literal types. See :pep:`586` and :class:`typing.Literal`.
1076 * "Final" variables, functions, methods and classes. See :pep:`591`,
1077 :class:`typing.Final` and :func:`typing.final`.
1079 * New protocol class :class:`typing.SupportsIndex`.
1081 * New functions :func:`typing.get_origin` and :func:`typing.get_args`.
1087 * The :mod:`unicodedata` module has been upgraded to use the `Unicode 12.1.0
1088 <http://blog.unicode.org/2019/05/unicode-12-1-en.html>`_ release.
1090 * New function :func:`~unicodedata.is_normalized` can be used to verify a string
1091 is in a specific normal form, often much faster than by actually normalizing
1092 the string. (Contributed by Max Belanger, David Euresti, and Greg Price in
1093 :issue:`32285` and :issue:`37966`).
1099 * Added :class:`AsyncMock` to support an asynchronous version of :class:`Mock`.
1100 Appropriate new assert functions for testing have been added as well.
1101 (Contributed by Lisa Roach in :issue:`26467`).
1103 * Added :func:`~unittest.addModuleCleanup()` and
1104 :meth:`~unittest.TestCase.addClassCleanup()` to unittest to support
1105 cleanups for :func:`~unittest.setUpModule()` and
1106 :meth:`~unittest.TestCase.setUpClass()`.
1107 (Contributed by Lisa Roach in :issue:`24412`.)
1109 * Several mock assert functions now also print a list of actual calls upon
1110 failure. (Contributed by Petter Strandmark in :issue:`35047`.)
1112 * :mod:`unittest` module gained support for coroutines to be used as test cases
1113 with :class:`unittest.IsolatedAsyncioTestCase`.
1114 (Contributed by Andrew Svetlov in :issue:`32972`.)
1121 class TestRequest(unittest.IsolatedAsyncioTestCase):
1123 async def asyncSetUp(self):
1124 self.connection = await AsyncConnection()
1126 async def test_get(self):
1127 response = await self.connection.get("https://example.com")
1128 self.assertEqual(response.status_code, 200)
1130 async def asyncTearDown(self):
1131 await self.connection.close()
1134 if __name__ == "__main__":
1141 * :mod:`venv` now includes an ``Activate.ps1`` script on all platforms for
1142 activating virtual environments under PowerShell Core 6.1.
1143 (Contributed by Brett Cannon in :issue:`32718`.)
1148 * The proxy objects returned by :func:`weakref.proxy` now support the matrix
1149 multiplication operators ``@`` and ``@=`` in addition to the other
1150 numeric operators. (Contributed by Mark Dickinson in :issue:`36669`.)
1155 * As mitigation against DTD and external entity retrieval, the
1156 :mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process
1157 external entities by default.
1158 (Contributed by Christian Heimes in :issue:`17239`.)
1160 * The ``.find*()`` methods in the :mod:`xml.etree.ElementTree` module
1161 support wildcard searches like ``{*}tag`` which ignores the namespace
1162 and ``{namespace}*`` which returns all tags in the given namespace.
1163 (Contributed by Stefan Behnel in :issue:`28238`.)
1165 * The :mod:`xml.etree.ElementTree` module provides a new function
1166 :func:`–xml.etree.ElementTree.canonicalize()` that implements C14N 2.0.
1167 (Contributed by Stefan Behnel in :issue:`13611`.)
1169 * The target object of :class:`xml.etree.ElementTree.XMLParser` can
1170 receive namespace declaration events through the new callback methods
1171 ``start_ns()`` and ``end_ns()``. Additionally, the
1172 :class:`xml.etree.ElementTree.TreeBuilder` target can be configured
1173 to process events about comments and processing instructions to include
1174 them in the generated tree.
1175 (Contributed by Stefan Behnel in :issue:`36676` and :issue:`36673`.)
1180 * The :mod:`subprocess` module can now use the :func:`os.posix_spawn` function
1181 in some cases for better performance. Currently, it is only used on macOS
1182 and Linux (using glibc 2.24 or newer) if all these conditions are met:
1184 * *close_fds* is false;
1185 * *preexec_fn*, *pass_fds*, *cwd* and *start_new_session* parameters
1187 * the *executable* path contains a directory.
1189 (Contributed by Joannah Nanjekye and Victor Stinner in :issue:`35537`.)
1191 * :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`,
1192 :func:`shutil.copytree` and :func:`shutil.move` use platform-specific
1193 "fast-copy" syscalls on Linux and macOS in order to copy the file
1195 "fast-copy" means that the copying operation occurs within the kernel,
1196 avoiding the use of userspace buffers in Python as in
1197 "``outfd.write(infd.read())``".
1198 On Windows :func:`shutil.copyfile` uses a bigger default buffer size (1 MiB
1199 instead of 16 KiB) and a :func:`memoryview`-based variant of
1200 :func:`shutil.copyfileobj` is used.
1201 The speedup for copying a 512 MiB file within the same partition is about
1202 +26% on Linux, +50% on macOS and +40% on Windows. Also, much less CPU cycles
1204 See :ref:`shutil-platform-dependent-efficient-copy-operations` section.
1205 (Contributed by Giampaolo Rodola' in :issue:`33671`.)
1207 * :func:`shutil.copytree` uses :func:`os.scandir` function and all copy
1208 functions depending from it use cached :func:`os.stat` values. The speedup
1209 for copying a directory with 8000 files is around +9% on Linux, +20% on
1210 Windows and +30% on a Windows SMB share. Also the number of :func:`os.stat`
1211 syscalls is reduced by 38% making :func:`shutil.copytree` especially faster
1212 on network filesystems. (Contributed by Giampaolo Rodola' in :issue:`33695`.)
1214 * The default protocol in the :mod:`pickle` module is now Protocol 4,
1215 first introduced in Python 3.4. It offers better performance and smaller
1216 size compared to Protocol 3 available since Python 3.0.
1218 * Removed one ``Py_ssize_t`` member from ``PyGC_Head``. All GC tracked
1219 objects (e.g. tuple, list, dict) size is reduced 4 or 8 bytes.
1220 (Contributed by Inada Naoki in :issue:`33597`)
1222 * :class:`uuid.UUID` now uses ``__slots__`` to reduce its memory footprint.
1224 * Improved performance of :func:`operator.itemgetter` by 33%. Optimized
1225 argument handling and added a fast path for the common case of a single
1226 non-negative integer index into a tuple (which is the typical use case in
1227 the standard library). (Contributed by Raymond Hettinger in
1230 * Sped-up field lookups in :func:`collections.namedtuple`. They are now more
1231 than two times faster, making them the fastest form of instance variable
1232 lookup in Python. (Contributed by Raymond Hettinger, Pablo Galindo, and
1233 Joe Jevnik, Serhiy Storchaka in :issue:`32492`.)
1235 * The :class:`list` constructor does not overallocate the internal item buffer
1236 if the input iterable has a known length (the input implements ``__len__``).
1237 This makes the created list 12% smaller on average. (Contributed by
1238 Raymond Hettinger and Pablo Galindo in :issue:`33234`.)
1240 * Doubled the speed of class variable writes. When a non-dunder attribute
1241 was updated, there was an unnecessary call to update slots.
1242 (Contributed by Stefan Behnel, Pablo Galindo Salgado, Raymond Hettinger,
1243 Neil Schemenauer, and Serhiy Storchaka in :issue:`36012`.)
1245 * Reduced an overhead of converting arguments passed to many builtin functions
1246 and methods. This sped up calling some simple builtin functions and
1247 methods up to 20--50%. (Contributed by Serhiy Storchaka in :issue:`23867`,
1248 :issue:`35582` and :issue:`36127`.)
1250 * ``LOAD_GLOBAL`` instruction now uses new "per opcode cache" mechanism.
1251 It is about 40% faster now. (Contributed by Yury Selivanov and Inada Naoki in
1255 Build and C API Changes
1256 =======================
1258 * Default :data:`sys.abiflags` became an empty string: the ``m`` flag for
1259 pymalloc became useless (builds with and without pymalloc are ABI compatible)
1260 and so has been removed. (Contributed by Victor Stinner in :issue:`36707`.)
1264 * Only ``python3.8`` program is installed, ``python3.8m`` program is gone.
1265 * Only ``python3.8-config`` script is installed, ``python3.8m-config`` script
1267 * The ``m`` flag has been removed from the suffix of dynamic library
1268 filenames: extension modules in the standard library as well as those
1269 produced and installed by third-party packages, like those downloaded from
1270 PyPI. On Linux, for example, the Python 3.7 suffix
1271 ``.cpython-37m-x86_64-linux-gnu.so`` became
1272 ``.cpython-38-x86_64-linux-gnu.so`` in Python 3.8.
1274 * The header files have been reorganized to better separate the different kinds
1277 * ``Include/*.h`` should be the portable public stable C API.
1278 * ``Include/cpython/*.h`` should be the unstable C API specific to CPython;
1279 public API, with some private API prefixed by ``_Py`` or ``_PY``.
1280 * ``Include/internal/*.h`` is the private internal C API very specific to
1281 CPython. This API comes with no backward compatibility warranty and should
1282 not be used outside CPython. It is only exposed for very specific needs
1283 like debuggers and profiles which has to access to CPython internals
1284 without calling functions. This API is now installed by ``make install``.
1286 (Contributed by Victor Stinner in :issue:`35134` and :issue:`35081`,
1287 work initiated by Eric Snow in Python 3.7)
1289 * Some macros have been converted to static inline functions: parameter types
1290 and return type are well defined, they don't have issues specific to macros,
1291 variables have a local scopes. Examples:
1293 * :c:func:`Py_INCREF`, :c:func:`Py_DECREF`
1294 * :c:func:`Py_XINCREF`, :c:func:`Py_XDECREF`
1295 * :c:func:`PyObject_INIT`, :c:func:`PyObject_INIT_VAR`
1296 * Private functions: :c:func:`_PyObject_GC_TRACK`,
1297 :c:func:`_PyObject_GC_UNTRACK`, :c:func:`_Py_Dealloc`
1299 (Contributed by Victor Stinner in :issue:`35059`.)
1301 * The :c:func:`PyByteArray_Init` and :c:func:`PyByteArray_Fini` functions have
1302 been removed. They did nothing since Python 2.7.4 and Python 3.2.0, were
1303 excluded from the limited API (stable ABI), and were not documented.
1304 (Contributed by Victor Stinner in :issue:`35713`.)
1306 * The result of :c:func:`PyExceptionClass_Name` is now of type
1307 ``const char *`` rather of ``char *``.
1308 (Contributed by Serhiy Storchaka in :issue:`33818`.)
1310 * The duality of ``Modules/Setup.dist`` and ``Modules/Setup`` has been
1311 removed. Previously, when updating the CPython source tree, one had
1312 to manually copy ``Modules/Setup.dist`` (inside the source tree) to
1313 ``Modules/Setup`` (inside the build tree) in order to reflect any changes
1314 upstream. This was of a small benefit to packagers at the expense of
1315 a frequent annoyance to developers following CPython development, as
1316 forgetting to copy the file could produce build failures.
1318 Now the build system always reads from ``Modules/Setup`` inside the source
1319 tree. People who want to customize that file are encouraged to maintain
1320 their changes in a git fork of CPython or as patch files, as they would do
1321 for any other change to the source tree.
1323 (Contributed by Antoine Pitrou in :issue:`32430`.)
1325 * Functions that convert Python number to C integer like
1326 :c:func:`PyLong_AsLong` and argument parsing functions like
1327 :c:func:`PyArg_ParseTuple` with integer converting format units like ``'i'``
1328 will now use the :meth:`~object.__index__` special method instead of
1329 :meth:`~object.__int__`, if available. The deprecation warning will be
1330 emitted for objects with the ``__int__()`` method but without the
1331 ``__index__()`` method (like :class:`~decimal.Decimal` and
1332 :class:`~fractions.Fraction`). :c:func:`PyNumber_Check` will now return
1333 ``1`` for objects implementing ``__index__()``.
1334 :c:func:`PyNumber_Long`, :c:func:`PyNumber_Float` and
1335 :c:func:`PyFloat_AsDouble` also now use the ``__index__()`` method if
1337 (Contributed by Serhiy Storchaka in :issue:`36048` and :issue:`20092`.)
1339 * Heap-allocated type objects will now increase their reference count
1340 in :c:func:`PyObject_Init` (and its parallel macro ``PyObject_INIT``)
1341 instead of in :c:func:`PyType_GenericAlloc`. Types that modify instance
1342 allocation or deallocation may need to be adjusted.
1343 (Contributed by Eddie Elizondo in :issue:`35810`.)
1345 * The new function :c:func:`PyCode_NewWithPosOnlyArgs` allows to create
1346 code objects like :c:func:`PyCode_New`, but with an extra *posonlyargcount*
1347 parameter for indicating the number of positional-only arguments.
1348 (Contributed by Pablo Galindo in :issue:`37221`.)
1350 * :c:func:`Py_SetPath` now sets :data:`sys.executable` to the program full
1351 path (:c:func:`Py_GetProgramFullPath`) rather than to the program name
1352 (:c:func:`Py_GetProgramName`).
1353 (Contributed by Victor Stinner in :issue:`38234`.)
1359 * The distutils ``bdist_wininst`` command is now deprecated, use
1360 ``bdist_wheel`` (wheel packages) instead.
1361 (Contributed by Victor Stinner in :issue:`37481`.)
1363 * Deprecated methods ``getchildren()`` and ``getiterator()`` in
1364 the :mod:`~xml.etree.ElementTree` module emit now a
1365 :exc:`DeprecationWarning` instead of :exc:`PendingDeprecationWarning`.
1366 They will be removed in Python 3.9.
1367 (Contributed by Serhiy Storchaka in :issue:`29209`.)
1369 * Passing an object that is not an instance of
1370 :class:`concurrent.futures.ThreadPoolExecutor` to
1371 :meth:`asyncio.loop.set_default_executor()` is
1372 deprecated and will be prohibited in Python 3.9.
1373 (Contributed by Elvis Pranskevichus in :issue:`34075`.)
1375 * The :meth:`__getitem__` methods of :class:`xml.dom.pulldom.DOMEventStream`,
1376 :class:`wsgiref.util.FileWrapper` and :class:`fileinput.FileInput` have been
1379 Implementations of these methods have been ignoring their *index* parameter,
1380 and returning the next item instead.
1382 (Contributed by Berker Peksag in :issue:`9372`.)
1384 * The :class:`typing.NamedTuple` class has deprecated the ``_field_types``
1385 attribute in favor of the ``__annotations__`` attribute which has the same
1386 information. (Contributed by Raymond Hettinger in :issue:`36320`.)
1388 * :mod:`ast` classes ``Num``, ``Str``, ``Bytes``, ``NameConstant`` and
1389 ``Ellipsis`` are considered deprecated and will be removed in future Python
1390 versions. :class:`~ast.Constant` should be used instead.
1391 (Contributed by Serhiy Storchaka in :issue:`32892`.)
1393 * :class:`ast.NodeVisitor` methods ``visit_Num()``, ``visit_Str()``,
1394 ``visit_Bytes()``, ``visit_NameConstant()`` and ``visit_Ellipsis()`` are
1395 deprecated now and will not be called in future Python versions.
1396 Add the :meth:`~ast.NodeVisitor.visit_Constant` method to handle all
1398 (Contributed by Serhiy Storchaka in :issue:`36917`.)
1400 * The following functions and methods are deprecated in the :mod:`gettext`
1401 module: :func:`~gettext.lgettext`, :func:`~gettext.ldgettext`,
1402 :func:`~gettext.lngettext` and :func:`~gettext.ldngettext`.
1403 They return encoded bytes, and it's possible that you will get unexpected
1404 Unicode-related exceptions if there are encoding problems with the
1405 translated strings. It's much better to use alternatives which return
1406 Unicode strings in Python 3. These functions have been broken for a long time.
1408 Function :func:`~gettext.bind_textdomain_codeset`, methods
1409 :meth:`~gettext.NullTranslations.output_charset` and
1410 :meth:`~gettext.NullTranslations.set_output_charset`, and the *codeset*
1411 parameter of functions :func:`~gettext.translation` and
1412 :func:`~gettext.install` are also deprecated, since they are only used for
1413 for the ``l*gettext()`` functions.
1415 (Contributed by Serhiy Storchaka in :issue:`33710`.)
1417 * The :meth:`~threading.Thread.isAlive()` method of :class:`threading.Thread` has been deprecated.
1418 (Contributed by Dong-hee Na in :issue:`35283`.)
1420 * Many builtin and extension functions that take integer arguments will
1421 now emit a deprecation warning for :class:`~decimal.Decimal`\ s,
1422 :class:`~fractions.Fraction`\ s and any other objects that can be converted
1423 to integers only with a loss (e.g. that have the :meth:`~object.__int__`
1424 method but do not have the :meth:`~object.__index__` method). In future
1425 version they will be errors.
1426 (Contributed by Serhiy Storchaka in :issue:`36048`.)
1428 * Deprecated passing the following arguments as keyword arguments:
1430 - *func* in :func:`functools.partialmethod`, :func:`weakref.finalize`,
1431 :meth:`profile.Profile.runcall`, :meth:`cProfile.Profile.runcall`,
1432 :meth:`bdb.Bdb.runcall`, :meth:`trace.Trace.runfunc` and
1433 :func:`curses.wrapper`.
1434 - *function* in :meth:`unittest.TestCase.addCleanup`.
1435 - *fn* in the :meth:`~concurrent.futures.Executor.submit` method of
1436 :class:`concurrent.futures.ThreadPoolExecutor` and
1437 :class:`concurrent.futures.ProcessPoolExecutor`.
1438 - *callback* in :meth:`contextlib.ExitStack.callback`,
1439 :meth:`contextlib.AsyncExitStack.callback` and
1440 :meth:`contextlib.AsyncExitStack.push_async_callback`.
1441 - *c* and *typeid* in the :meth:`~multiprocessing.managers.Server.create`
1442 method of :class:`multiprocessing.managers.Server` and
1443 :class:`multiprocessing.managers.SharedMemoryServer`.
1444 - *obj* in :func:`weakref.finalize`.
1446 In future releases of Python they will be :ref:`positional-only
1447 <positional-only_parameter>`.
1448 (Contributed by Serhiy Storchaka in :issue:`36492`.)
1451 API and Feature Removals
1452 ========================
1454 The following features and APIs have been removed from Python 3.8:
1456 * The :mod:`macpath` module, deprecated in Python 3.7, has been removed.
1457 (Contributed by Victor Stinner in :issue:`35471`.)
1459 * The function :func:`platform.popen` has been removed, it was deprecated since
1460 Python 3.3: use :func:`os.popen` instead.
1461 (Contributed by Victor Stinner in :issue:`35345`.)
1463 * The function :func:`time.clock` has been removed, it was deprecated since Python
1464 3.3: use :func:`time.perf_counter` or :func:`time.process_time` instead, depending
1465 on your requirements, to have a well defined behavior.
1466 (Contributed by Matthias Bussonnier in :issue:`36895`.)
1468 * The ``pyvenv`` script has been removed in favor of ``python3.8 -m venv``
1469 to help eliminate confusion as to what Python interpreter the ``pyvenv``
1470 script is tied to. (Contributed by Brett Cannon in :issue:`25427`.)
1472 * ``parse_qs``, ``parse_qsl``, and ``escape`` are removed from :mod:`cgi`
1473 module. They are deprecated from Python 3.2 or older. They should be imported
1474 from the ``urllib.parse`` and ``html`` modules instead.
1476 * ``filemode`` function is removed from :mod:`tarfile` module.
1477 It is not documented and deprecated since Python 3.3.
1479 * The :class:`~xml.etree.ElementTree.XMLParser` constructor no longer accepts
1480 the *html* argument. It never had effect and was deprecated in Python 3.4.
1481 All other parameters are now :ref:`keyword-only <keyword-only_parameter>`.
1482 (Contributed by Serhiy Storchaka in :issue:`29209`.)
1484 * Removed the ``doctype()`` method of :class:`~xml.etree.ElementTree.XMLParser`.
1485 (Contributed by Serhiy Storchaka in :issue:`29209`.)
1487 * "unicode_internal" codec is removed.
1488 (Contributed by Inada Naoki in :issue:`36297`.)
1490 * The ``Cache`` and ``Statement`` objects of the :mod:`sqlite3` module are not
1491 exposed to the user.
1492 (Contributed by Aviv Palivoda in :issue:`30262`.)
1494 * The ``bufsize`` keyword argument of :func:`fileinput.input` and
1495 :func:`fileinput.FileInput` which was ignored and deprecated since Python 3.6
1496 has been removed. :issue:`36952` (Contributed by Matthias Bussonnier)
1498 * The functions :func:`sys.set_coroutine_wrapper` and
1499 :func:`sys.get_coroutine_wrapper` deprecated in Python 3.7 have been removed;
1500 :issue:`36933` (Contributed by Matthias Bussonnier)
1503 Porting to Python 3.8
1504 =====================
1506 This section lists previously described changes and other bugfixes
1507 that may require changes to your code.
1510 Changes in Python behavior
1511 --------------------------
1513 * Yield expressions (both ``yield`` and ``yield from`` clauses) are now disallowed
1514 in comprehensions and generator expressions (aside from the iterable expression
1515 in the leftmost :keyword:`!for` clause).
1516 (Contributed by Serhiy Storchaka in :issue:`10544`.)
1518 * The compiler now produces a :exc:`SyntaxWarning` when identity checks
1519 (``is`` and ``is not``) are used with certain types of literals
1520 (e.g. strings, ints). These can often work by accident in CPython,
1521 but are not guaranteed by the language spec. The warning advises users
1522 to use equality tests (``==`` and ``!=``) instead.
1523 (Contributed by Serhiy Storchaka in :issue:`34850`.)
1525 * The CPython interpreter can swallow exceptions in some circumstances.
1526 In Python 3.8 this happens in less cases. In particular, exceptions
1527 raised when getting the attribute from the type dictionary are no longer
1528 ignored. (Contributed by Serhiy Storchaka in :issue:`35459`.)
1530 * Removed ``__str__`` implementations from builtin types :class:`bool`,
1531 :class:`int`, :class:`float`, :class:`complex` and few classes from
1532 the standard library. They now inherit ``__str__()`` from :class:`object`.
1533 As result, defining the ``__repr__()`` method in the subclass of these
1534 classes will affect their string representation.
1535 (Contributed by Serhiy Storchaka in :issue:`36793`.)
1537 * On AIX, :attr:`sys.platform` doesn't contain the major version anymore.
1538 It is always ``'aix'``, instead of ``'aix3'`` .. ``'aix7'``. Since
1539 older Python versions include the version number, it is recommended to
1540 always use the ``sys.platform.startswith('aix')``.
1541 (Contributed by M. Felt in :issue:`36588`.)
1543 * :c:func:`PyEval_AcquireLock` and :c:func:`PyEval_AcquireThread` now
1544 terminate the current thread if called while the interpreter is
1545 finalizing, making them consistent with :c:func:`PyEval_RestoreThread`,
1546 :c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`. If this
1547 behaviour is not desired, guard the call by checking :c:func:`_Py_IsFinalizing`
1548 or :c:func:`sys.is_finalizing`.
1550 Changes in the Python API
1551 -------------------------
1553 * The :func:`os.getcwdb` function now uses the UTF-8 encoding on Windows,
1554 rather than the ANSI code page: see :pep:`529` for the rationale. The
1555 function is no longer deprecated on Windows.
1556 (Contributed by Victor Stinner in :issue:`37412`.)
1558 * :class:`subprocess.Popen` can now use :func:`os.posix_spawn` in some cases
1559 for better performance. On Windows Subsystem for Linux and QEMU User
1560 Emulation, Popen constructor using :func:`os.posix_spawn` no longer raise an
1561 exception on errors like missing program, but the child process fails with a
1562 non-zero :attr:`~Popen.returncode`.
1563 (Contributed by Joannah Nanjekye and Victor Stinner in :issue:`35537`.)
1565 * The *preexec_fn* argument of * :class:`subprocess.Popen` is no longer
1566 compatible with subinterpreters. The use of the parameter in a
1567 subinterpreter now raises :exc:`RuntimeError`.
1568 (Contributed by Eric Snow in :issue:`34651`, modified by Christian Heimes
1571 * The :meth:`imap.IMAP4.logout` method no longer ignores silently arbitrary
1574 * The function :func:`platform.popen` has been removed, it was deprecated since
1575 Python 3.3: use :func:`os.popen` instead.
1576 (Contributed by Victor Stinner in :issue:`35345`.)
1578 * The :func:`statistics.mode` function no longer raises an exception
1579 when given multimodal data. Instead, it returns the first mode
1580 encountered in the input data. (Contributed by Raymond Hettinger
1583 * The :meth:`~tkinter.ttk.Treeview.selection` method of the
1584 :class:`tkinter.ttk.Treeview` class no longer takes arguments. Using it with
1585 arguments for changing the selection was deprecated in Python 3.6. Use
1586 specialized methods like :meth:`~tkinter.ttk.Treeview.selection_set` for
1587 changing the selection. (Contributed by Serhiy Storchaka in :issue:`31508`.)
1589 * The :meth:`writexml`, :meth:`toxml` and :meth:`toprettyxml` methods of the
1590 :mod:`xml.dom.minidom` module, and :mod:`xml.etree` now preserve the attribute
1591 order specified by the user.
1592 (Contributed by Diego Rojas and Raymond Hettinger in :issue:`34160`.)
1594 * A :mod:`dbm.dumb` database opened with flags ``'r'`` is now read-only.
1595 :func:`dbm.dumb.open` with flags ``'r'`` and ``'w'`` no longer creates
1596 a database if it does not exist.
1597 (Contributed by Serhiy Storchaka in :issue:`32749`.)
1599 * The ``doctype()`` method defined in a subclass of
1600 :class:`~xml.etree.ElementTree.XMLParser` will no longer be called and will
1601 cause emitting a :exc:`RuntimeWarning` instead of a :exc:`DeprecationWarning`.
1602 Define the :meth:`doctype() <xml.etree.ElementTree.TreeBuilder.doctype>`
1603 method on a target for handling an XML doctype declaration.
1604 (Contributed by Serhiy Storchaka in :issue:`29209`.)
1606 * A :exc:`RuntimeError` is now raised when the custom metaclass doesn't
1607 provide the ``__classcell__`` entry in the namespace passed to
1608 ``type.__new__``. A :exc:`DeprecationWarning` was emitted in Python
1609 3.6--3.7. (Contributed by Serhiy Storchaka in :issue:`23722`.)
1611 * The :class:`cProfile.Profile` class can now be used as a context
1612 manager. (Contributed by Scott Sanderson in :issue:`29235`.)
1614 * :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`,
1615 :func:`shutil.copytree` and :func:`shutil.move` use platform-specific
1616 "fast-copy" syscalls (see
1617 :ref:`shutil-platform-dependent-efficient-copy-operations` section).
1619 * :func:`shutil.copyfile` default buffer size on Windows was changed from
1622 * The ``PyGC_Head`` struct has changed completely. All code that touched the
1623 struct member should be rewritten. (See :issue:`33597`)
1625 * The ``PyInterpreterState`` struct has been moved into the "internal"
1626 header files (specifically Include/internal/pycore_pystate.h). An
1627 opaque ``PyInterpreterState`` is still available as part of the public
1628 API (and stable ABI). The docs indicate that none of the struct's
1629 fields are public, so we hope no one has been using them. However,
1630 if you do rely on one or more of those private fields and have no
1631 alternative then please open a BPO issue. We'll work on helping
1632 you adjust (possibly including adding accessor functions to the
1633 public API). (See :issue:`35886`.)
1635 * Asyncio tasks can now be named, either by passing the ``name`` keyword
1636 argument to :func:`asyncio.create_task` or
1637 the :meth:`~asyncio.loop.create_task` event loop method, or by
1638 calling the :meth:`~asyncio.Task.set_name` method on the task object. The
1639 task name is visible in the ``repr()`` output of :class:`asyncio.Task` and
1640 can also be retrieved using the :meth:`~asyncio.Task.get_name` method.
1642 * The :meth:`mmap.flush() <mmap.mmap.flush>` method now returns ``None`` on
1643 success and raises an exception on error under all platforms. Previously,
1644 its behavior was platform-depended: a nonzero value was returned on success;
1645 zero was returned on error under Windows. A zero value was returned on
1646 success; an exception was raised on error under Unix.
1647 (Contributed by Berker Peksag in :issue:`2122`.)
1649 * :mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process
1650 external entities by default.
1651 (Contributed by Christian Heimes in :issue:`17239`.)
1653 * Deleting a key from a read-only :mod:`dbm` database (:mod:`dbm.dumb`,
1654 :mod:`dbm.gnu` or :mod:`dbm.ndbm`) raises :attr:`error` (:exc:`dbm.dumb.error`,
1655 :exc:`dbm.gnu.error` or :exc:`dbm.ndbm.error`) instead of :exc:`KeyError`.
1656 (Contributed by Xiang Zhang in :issue:`33106`.)
1658 * :func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE`
1659 environment variable and does not use :envvar:`HOME`, which is not normally
1660 set for regular user accounts.
1662 * The Exception :class:`asyncio.CancelledError` now inherits from
1663 :class:`BaseException` rather than a :class:`Exception`.
1664 (Contributed by Yury Selivanov in :issue:`13528`.)
1666 .. _bpo-36085-whatsnew:
1668 * DLL dependencies for extension modules and DLLs loaded with :mod:`ctypes` on
1669 Windows are now resolved more securely. Only the system paths, the directory
1670 containing the DLL or PYD file, and directories added with
1671 :func:`~os.add_dll_directory` are searched for load-time dependencies.
1672 Specifically, :envvar:`PATH` and the current working directory are no longer
1673 used, and modifications to these will no longer have any effect on normal DLL
1674 resolution. If your application relies on these mechanisms, you should check
1675 for :func:`~os.add_dll_directory` and if it exists, use it to add your DLLs
1676 directory while loading your library. Note that Windows 7 users will need to
1677 ensure that Windows Update KB2533625 has been installed (this is also verified
1679 (See :issue:`36085`.)
1681 * The header files and functions related to pgen have been removed after its
1682 replacement by a pure Python implementation. (Contributed by Pablo Galindo
1685 * :class:`types.CodeType` has a new parameter in the second position of the
1686 constructor (*posonlyargcount*) to support positional-only arguments defined
1687 in :pep:`570`. The first argument (*argcount*) now represents the total
1688 number of positional arguments (including positional-only arguments). A new
1689 ``replace()`` method of :class:`types.CodeType` can be used to make the code
1693 Changes in the C API
1694 --------------------
1696 * The :c:type:`PyCompilerFlags` structure gets a new *cf_feature_version*
1697 field. It should be initialized to ``PY_MINOR_VERSION``. The field is ignored
1698 by default, it is used if and only if ``PyCF_ONLY_AST`` flag is set in
1701 * The :c:func:`PyEval_ReInitThreads` function has been removed from the C API.
1702 It should not be called explicitly: use :c:func:`PyOS_AfterFork_Child`
1704 (Contributed by Victor Stinner in :issue:`36728`.)
1706 * On Unix, C extensions are no longer linked to libpython except on Android
1707 and Cygwin. When Python is embedded, ``libpython`` must not be loaded with
1708 ``RTLD_LOCAL``, but ``RTLD_GLOBAL`` instead. Previously, using
1709 ``RTLD_LOCAL``, it was already not possible to load C extensions which
1710 were not linked to ``libpython``, like C extensions of the standard
1711 library built by the ``*shared*`` section of ``Modules/Setup``.
1712 (Contributed by Victor Stinner in :issue:`21536`.)
1714 * Use of ``#`` variants of formats in parsing or building value (e.g.
1715 :c:func:`PyArg_ParseTuple`, :c:func:`Py_BuildValue`, :c:func:`PyObject_CallFunction`,
1716 etc.) without ``PY_SSIZE_T_CLEAN`` defined raises ``DeprecationWarning`` now.
1717 It will be removed in 3.10 or 4.0. Read :ref:`arg-parsing` for detail.
1718 (Contributed by Inada Naoki in :issue:`36381`.)
1720 * Instances of heap-allocated types (such as those created with
1721 :c:func:`PyType_FromSpec`) hold a reference to their type object.
1722 Increasing the reference count of these type objects has been moved from
1723 :c:func:`PyType_GenericAlloc` to the more low-level functions,
1724 :c:func:`PyObject_Init` and :c:func:`PyObject_INIT`.
1725 This makes types created through :c:func:`PyType_FromSpec` behave like
1726 other classes in managed code.
1728 Statically allocated types are not affected.
1730 For the vast majority of cases, there should be no side effect.
1731 However, types that manually increase the reference count after allocating
1732 an instance (perhaps to work around the bug) may now become immortal.
1733 To avoid this, these classes need to call Py_DECREF on the type object
1734 during instance deallocation.
1736 To correctly port these types into 3.8, please apply the following
1739 * Remove :c:macro:`Py_INCREF` on the type object after allocating an
1741 This may happen after calling :c:func:`PyObject_New`,
1742 :c:func:`PyObject_NewVar`, :c:func:`PyObject_GC_New`,
1743 :c:func:`PyObject_GC_NewVar`, or any other custom allocator that uses
1744 :c:func:`PyObject_Init` or :c:func:`PyObject_INIT`.
1749 foo_new(PyObject *type) {
1750 foo_struct *foo = PyObject_GC_New(foo_struct, (PyTypeObject *) type);
1753 #if PY_VERSION_HEX < 0x03080000
1754 // Workaround for Python issue 35810; no longer necessary in Python 3.8
1760 * Ensure that all custom ``tp_dealloc`` functions of heap-allocated types
1761 decrease the type's reference count.
1766 foo_dealloc(foo_struct *instance) {
1767 PyObject *type = Py_TYPE(instance);
1768 PyObject_GC_Del(instance);
1769 #if PY_VERSION_HEX >= 0x03080000
1770 // This was not needed before Python 3.8 (Python issue 35810)
1775 (Contributed by Eddie Elizondo in :issue:`35810`.)
1777 * The :c:macro:`Py_DEPRECATED()` macro has been implemented for MSVC.
1778 The macro now must be placed before the symbol name.
1782 Py_DEPRECATED(3.8) PyAPI_FUNC(int) Py_OldFunction(void);
1784 (Contributed by Zackery Spytz in :issue:`33407`.)
1786 * The interpreter does not pretend to support binary compatibility of
1787 extension types across feature releases, anymore. A :c:type:`PyTypeObject`
1788 exported by a third-party extension module is supposed to have all the
1789 slots expected in the current Python version, including
1790 :c:member:`~PyTypeObject.tp_finalize` (:const:`Py_TPFLAGS_HAVE_FINALIZE`
1791 is not checked anymore before reading :c:member:`~PyTypeObject.tp_finalize`).
1793 (Contributed by Antoine Pitrou in :issue:`32388`.)
1795 * The :c:func:`PyCode_New` has a new parameter in the second position (*posonlyargcount*)
1796 to support :pep:`570`, indicating the number of positional-only arguments.
1798 * The functions :c:func:`PyNode_AddChild` and :c:func:`PyParser_AddToken` now accept
1799 two additional ``int`` arguments *end_lineno* and *end_col_offset*.
1801 .. highlight:: shell
1803 * The :file:`libpython38.a` file to allow MinGW tools to link directly against
1804 :file:`python38.dll` is no longer included in the regular Windows distribution.
1805 If you require this file, it may be generated with the ``gendef`` and
1806 ``dlltool`` tools, which are part of the MinGW binutils package::
1808 gendef python38.dll > tmp.def
1809 dlltool --dllname python38.dll --def tmp.def --output-lib libpython38.a
1811 The location of an installed :file:`pythonXY.dll` will depend on the
1812 installation options and the version and language of Windows. See
1813 :ref:`using-on-windows` for more information. The resulting library should be
1814 placed in the same directory as :file:`pythonXY.lib`, which is generally the
1815 :file:`libs` directory under your Python installation.
1817 .. highlight:: python3
1820 CPython bytecode changes
1821 ------------------------
1823 * The interpreter loop has been simplified by moving the logic of unrolling
1824 the stack of blocks into the compiler. The compiler emits now explicit
1825 instructions for adjusting the stack of values and calling the
1826 cleaning-up code for :keyword:`break`, :keyword:`continue` and
1829 Removed opcodes :opcode:`BREAK_LOOP`, :opcode:`CONTINUE_LOOP`,
1830 :opcode:`SETUP_LOOP` and :opcode:`SETUP_EXCEPT`. Added new opcodes
1831 :opcode:`ROT_FOUR`, :opcode:`BEGIN_FINALLY`, :opcode:`CALL_FINALLY` and
1832 :opcode:`POP_FINALLY`. Changed the behavior of :opcode:`END_FINALLY`
1833 and :opcode:`WITH_CLEANUP_START`.
1835 (Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka in
1838 * Added new opcode :opcode:`END_ASYNC_FOR` for handling exceptions raised
1839 when awaiting a next item in an :keyword:`async for` loop.
1840 (Contributed by Serhiy Storchaka in :issue:`33041`.)
1842 * The :opcode:`MAP_ADD` now expects the value as the first element in the
1843 stack and the key as the second element. This change was made so the key
1844 is always evaluated before the value in dictionary comprehensions, as
1845 proposed by :pep:`572`. (Contributed by Jörn Heissler in :issue:`35224`.)
1851 * Added a benchmark script for timing various ways to access variables:
1852 ``Tools/scripts/var_access_benchmark.py``.
1853 (Contributed by Raymond Hettinger in :issue:`35884`.)