Doc/whatsnew/3.8.rst
What's New In Python 3.8
.. Rules for maintenance:
Anyone can add text to this document. Do not spend very much time on the wording of your changes, because your text will probably get rewritten to some degree.
The maintainer will go through Misc/NEWS periodically and add changes; it's therefore more important to add your changes to Misc/NEWS than to this file.
This is not a complete list of every single change; completeness is the purpose of Misc/NEWS. Some changes I consider too small or esoteric to include. If such a change is added to the text, I'll just remove it. (This is another reason you shouldn't spend too much time on writing your addition.)
If you want to draw your new text to the attention of the maintainer, add 'XXX' to the beginning of the paragraph or section.
It's OK to just add a fragmentary note about a change. For example: "XXX Describe the transmogrify() function added to the socket module." The maintainer will research the change and write the necessary text.
You can comment out your additions if you like, but it's not necessary (especially when a final release is some months away).
Credit the author of a patch or bugfix. Just the name is sufficient; the e-mail address isn't necessary.
It's helpful to add the bug/patch number as a comment:
XXX Describe the transmogrify() function added to the socket
module.
(Contributed by P.Y. Developer in :issue:12345.)
This saves the maintainer the effort of going through the Git log when researching a change.
:Editor: Raymond Hettinger
This article explains the new features in Python 3.8, compared to 3.7.
Python 3.8 was released on October 14, 2019.
For full details, see the :ref:changelog <changelog>.
.. testsetup::
from math import cos, radians from unicodedata import normalize import re import math
.. This section singles out the most important changes in Python 3.8. Brevity is key.
.. PEP-sized items next.
There is new syntax := that assigns values to variables as part of a larger
expression. It is affectionately known as "the walrus operator" due to
its resemblance to the eyes and tusks of a walrus <https://en.wikipedia.org/wiki/Walrus#/media/File:Pacific_Walrus_-_Bull_(8247646168).jpg>_.
In this example, the assignment expression helps avoid calling
:func:len twice::
if (n := len(a)) > 10: print(f"List is too long ({n} elements, expected <= 10)")
A similar benefit arises during regular expression matching where match objects are needed twice, once to test whether a match occurred and another to extract a subgroup::
discount = 0.0 if (mo := re.search(r'(\d+)% discount', advertisement)): discount = float(mo.group(1)) / 100.0
The operator is also useful with while-loops that compute a value to test loop termination and then need that same value again in the body of the loop::
while (block := f.read(256)) != '': process(block)
Another motivating use case arises in list comprehensions where a value computed in a filtering condition is also needed in the expression body::
[clean_name.title() for name in names if (clean_name := normalize('NFC', name)) in allowed_names]
Try to limit use of the walrus operator to clean cases that reduce complexity and improve readability.
See :pep:572 for a full description.
(Contributed by Emily Morehouse in :issue:35224.)
There is a new function parameter syntax / to indicate that some
function parameters must be specified positionally and cannot be used as
keyword arguments. This is the same notation shown by help() for C
functions annotated with Larry Hastings'
Argument Clinic <https://devguide.python.org/development-tools/clinic/>__ tool.
In the following example, parameters a and b are positional-only, while c or d can be positional or keyword, and e or f are required to be keywords::
def f(a, b, /, c, d, *, e, f): print(a, b, c, d, e, f)
The following is a valid call::
f(10, 20, 30, d=40, e=50, f=60)
However, these are invalid calls::
f(10, b=20, c=30, d=40, e=50, f=60) # b cannot be a keyword argument f(10, 20, 30, 40, 50, f=60) # e must be a keyword argument
One use case for this notation is that it allows pure Python functions
to fully emulate behaviors of existing C coded functions. For example,
the built-in :func:divmod function does not accept keyword arguments::
def divmod(a, b, /): "Emulate the built in divmod() function" return (a // b, a % b)
Another use case is to preclude keyword arguments when the parameter
name is not helpful. For example, the builtin :func:len function has
the signature len(obj, /). This precludes awkward calls such as::
len(obj='hello') # The "obj" keyword argument impairs readability
A further benefit of marking a parameter as positional-only is that it
allows the parameter name to be changed in the future without risk of
breaking client code. For example, in the :mod:statistics module, the
parameter name dist may be changed in the future. This was made
possible with the following function specification::
def quantiles(dist, /, *, n=4, method='exclusive') ...
Since the parameters to the left of / are not exposed as possible
keywords, the parameters names remain available for use in **kwargs::
def f(a, b, /, **kwargs): ... print(a, b, kwargs) ... f(10, 20, a=1, b=2, c=3) # a and b are used in two ways 10 20 {'a': 1, 'b': 2, 'c': 3}
This greatly simplifies the implementation of functions and methods
that need to accept arbitrary keyword arguments. For example, here
is an excerpt from code in the :mod:collections module::
class Counter(dict):
def __init__(self, iterable=None, /, **kwds):
# Note "iterable" is a possible keyword argument
See :pep:570 for a full description.
(Contributed by Pablo Galindo in :issue:36540.)
.. TODO: Pablo will sprint on docs at PyCon US 2019.
The new :envvar:PYTHONPYCACHEPREFIX setting (also available as
:option:-X pycache_prefix) configures the implicit bytecode
cache to use a separate parallel filesystem tree, rather than
the default __pycache__ subdirectories within each source
directory.
The location of the cache is reported in :data:sys.pycache_prefix
(:const:None indicates the default location in __pycache__
subdirectories).
(Contributed by Carl Meyer in :issue:33499.)
The ABI of Python :ref:debug builds <debug-build> is now compatible with
Python release builds. On Unix, when Python is built in debug mode, it is now
possible to load C extensions built in release mode and C extensions built
using the stable ABI. The inverse is not true, as debug builds expose
additional symbols not available in release builds.
Defining the Py_DEBUG macro no longer implies the Py_TRACE_REFS macro,
which introduces the only ABI incompatibility. The Py_TRACE_REFS macro,
which adds the :func:sys.getobjects function and the :envvar:PYTHONDUMPREFS
environment variable, can be set using the new :option:./configure --with-trace-refs <--with-trace-refs> build option.
(Contributed by Victor Stinner in :issue:36465.)
On Unix, C extensions are no longer linked to libpython except on Android
and Cygwin.
It is now possible
for a statically linked Python to load a C extension built using a shared
library Python.
(Contributed by Victor Stinner in :issue:21536.)
On Unix, when Python is built in debug mode, import now also looks for C
extensions compiled in release mode and for C extensions compiled with the
stable ABI.
(Contributed by Victor Stinner in :issue:36722.)
To embed Python into an application, a new --embed option must be passed to
python3-config --libs --embed to get -lpython3.8 (link the application
to libpython). To support both 3.8 and older, try python3-config --libs --embed first and fallback to python3-config --libs (without --embed)
if the previous command fails.
Add a pkg-config python-3.8-embed module to embed Python into an
application: pkg-config python-3.8-embed --libs includes -lpython3.8.
To support both 3.8 and older, try pkg-config python-X.Y-embed --libs first
and fallback to pkg-config python-X.Y --libs (without --embed) if the
previous command fails (replace X.Y with the Python version).
On the other hand, pkg-config python3.8 --libs no longer contains
-lpython3.8. C extensions must not be linked to libpython (except on
Android and Cygwin, whose cases are handled by the script);
this change is backward incompatible on purpose.
(Contributed by Victor Stinner in :issue:36721.)
.. _bpo-36817-whatsnew:
= for self-documenting expressions and debuggingAdded an = specifier to :term:f-string\s. An f-string such as
f'{expr=}' will expand to the text of the expression, an equal sign,
then the representation of the evaluated expression. For example:
import datetime as dt user = 'eric_idle' member_since = dt.date(1975, 7, 31) f'{user=} {member_since=}' "user='eric_idle' member_since=datetime.date(1975, 7, 31)"
The usual :ref:f-string format specifiers <f-strings> allow more
control over how the result of the expression is displayed::
delta = dt.date.today() - member_since f'{user=!s} {delta.days=:,d}' 'user=eric_idle delta.days=16,075'
The = specifier will display the whole expression so that
calculations can be shown::
print(f'{theta=} {cos(radians(theta))=:.3f}') theta=30 cos(radians(theta))=0.866
(Contributed by Eric V. Smith and Larry Hastings in :issue:36817.)
The PEP adds an Audit Hook and Verified Open Hook. Both are available from Python and native code, allowing applications and frameworks written in pure Python code to take advantage of extra notifications, while also allowing embedders or system administrators to deploy builds of Python where auditing is always enabled.
See :pep:578 for full details.
The :pep:587 adds a new C API to configure the Python Initialization
providing finer control on the whole configuration and better error reporting.
New structures:
PyConfigPyPreConfigPyStatusPyWideStringListNew functions:
PyConfig_ClearPyConfig_InitIsolatedConfigPyConfig_InitPythonConfigPyConfig_ReadPyConfig_SetArgvPyConfig_SetBytesArgvPyConfig_SetBytesStringPyConfig_SetStringPyPreConfig_InitIsolatedConfigPyPreConfig_InitPythonConfigPyStatus_ErrorPyStatus_ExceptionPyStatus_ExitPyStatus_IsErrorPyStatus_IsExitPyStatus_NoMemoryPyStatus_OkPyWideStringList_AppendPyWideStringList_InsertPy_BytesMainPy_ExitStatusExceptionPy_InitializeFromConfigPy_PreInitializePy_PreInitializeFromArgsPy_PreInitializeFromBytesArgsPy_RunMainThis PEP also adds _PyRuntimeState.preconfig (:c:type:PyPreConfig type)
and PyInterpreterState.config (:c:type:PyConfig type) fields to these
internal structures. PyInterpreterState.config becomes the new
reference configuration, replacing global configuration variables and
other private variables.
See :ref:Python Initialization Configuration <init-config> for the
documentation.
See :pep:587 for a full description.
(Contributed by Victor Stinner in :issue:36763.)
:ref:vectorcall is added to the Python/C API.
It is meant to formalize existing optimizations which were already done
for various classes.
Any :ref:static type <static-types> implementing a callable can use this
protocol.
This is currently provisional. The aim is to make it fully public in Python 3.9.
See :pep:590 for a full description.
(Contributed by Jeroen Demeyer, Mark Shannon and Petr Viktorin in :issue:36974.)
When :mod:pickle is used to transfer large data between Python processes
in order to take advantage of multi-core or multi-machine processing,
it is important to optimize the transfer by reducing memory copies, and
possibly by applying custom techniques such as data-dependent compression.
The :mod:pickle protocol 5 introduces support for out-of-band buffers
where :pep:3118-compatible data can be transmitted separately from the
main pickle stream, at the discretion of the communication layer.
See :pep:574 for a full description.
(Contributed by Antoine Pitrou in :issue:36785.)
A :keyword:continue statement was illegal in the :keyword:finally clause
due to a problem with the implementation. In Python 3.8 this restriction
was lifted.
(Contributed by Serhiy Storchaka in :issue:32489.)
The :class:bool, :class:int, and :class:fractions.Fraction types
now have an :meth:~int.as_integer_ratio method like that found in
:class:float and :class:decimal.Decimal. This minor API extension
makes it possible to write numerator, denominator = x.as_integer_ratio() and have it work across multiple numeric types.
(Contributed by Lisa Roach in :issue:33073 and Raymond Hettinger in
:issue:37819.)
Constructors of :class:int, :class:float and :class:complex will now
use the :meth:~object.__index__ special method, if available and the
corresponding method :meth:~object.__int__, :meth:~object.__float__
or :meth:~object.__complex__ is not available.
(Contributed by Serhiy Storchaka in :issue:20092.)
Added support of :samp:\\N\\{{name}\\} escapes in :mod:regular expressions <re>::
notice = 'Copyright © 2019' copyright_year_pattern = re.compile(r'\N{copyright sign}\s*(\d{4})') int(copyright_year_pattern.search(notice).group(1)) 2019
(Contributed by Jonathan Eunice and Serhiy Storchaka in :issue:30688.)
Dict and dictviews are now iterable in reversed insertion order using
:func:reversed. (Contributed by Rémi Lapeyre in :issue:33462.)
The syntax allowed for keyword names in function calls was further
restricted. In particular, f((keyword)=arg) is no longer allowed. It was
never intended to permit more than a bare name on the left-hand side of a
keyword argument assignment term.
(Contributed by Benjamin Peterson in :issue:34641.)
Generalized iterable unpacking in :keyword:yield and
:keyword:return statements no longer requires enclosing parentheses.
This brings the yield and return syntax into better agreement with
normal assignment syntax::
def parse(family): ... lastname, *members = family.split() ... return lastname.upper(), *members ... parse('simpsons homer marge bart lisa maggie') ('SIMPSONS', 'homer', 'marge', 'bart', 'lisa', 'maggie')
(Contributed by David Cuthbert and Jordan Chapman in :issue:32117.)
When a comma is missed in code such as [(10, 20) (30, 40)], the
compiler displays a :exc:SyntaxWarning with a helpful suggestion.
This improves on just having a :exc:TypeError indicating that the
first tuple was not callable. (Contributed by Serhiy Storchaka in
:issue:15248.)
Arithmetic operations between subclasses of :class:datetime.date or
:class:datetime.datetime and :class:datetime.timedelta objects now return
an instance of the subclass, rather than the base class. This also affects
the return type of operations whose implementation (directly or indirectly)
uses :class:datetime.timedelta arithmetic, such as
:meth:~datetime.datetime.astimezone.
(Contributed by Paul Ganssle in :issue:32417.)
When the Python interpreter is interrupted by Ctrl-C (SIGINT) and the
resulting :exc:KeyboardInterrupt exception is not caught, the Python process
now exits via a SIGINT signal or with the correct exit code such that the
calling process can detect that it died due to a Ctrl-C. Shells on POSIX
and Windows use this to properly terminate scripts in interactive sessions.
(Contributed by Google via Gregory P. Smith in :issue:1054041.)
Some advanced styles of programming require updating the
:class:types.CodeType object for an existing function. Since code
objects are immutable, a new code object needs to be created, one
that is modeled on the existing code object. With 19 parameters,
this was somewhat tedious. Now, the new replace() method makes
it possible to create a clone with a few altered parameters.
Here's an example that alters the :func:statistics.mean function to
prevent the data parameter from being used as a keyword argument::
from statistics import mean mean(data=[10, 20, 90]) 40 mean.code = mean.code.replace(co_posonlyargcount=1) mean(data=[10, 20, 90]) Traceback (most recent call last): ... TypeError: mean() got some positional-only arguments passed as keyword arguments: 'data'
(Contributed by Victor Stinner in :issue:37032.)
For integers, the three-argument form of the :func:pow function now
permits the exponent to be negative in the case where the base is
relatively prime to the modulus. It then computes a modular inverse to
the base when the exponent is -1, and a suitable power of that
inverse for other negative exponents. For example, to compute the
modular multiplicative inverse <https://en.wikipedia.org/wiki/Modular_multiplicative_inverse>_ of 38
modulo 137, write::
pow(38, -1, 137) 119 119 * 38 % 137 1
Modular inverses arise in the solution of linear Diophantine equations <https://en.wikipedia.org/wiki/Diophantine_equation>_.
For example, to find integer solutions for 4258𝑥 + 147𝑦 = 369,
first rewrite as 4258𝑥 ≡ 369 (mod 147) then solve:
x = 369 * pow(4258, -1, 147) % 147 y = (4258 * x - 369) // -147 4258 * x + 147 * y 369
(Contributed by Mark Dickinson in :issue:36027.)
Dict comprehensions have been synced-up with dict literals so that the key is computed first and the value second::
Dict comprehension
cast = {input('role? '): input('actor? ') for i in range(2)} role? King Arthur actor? Chapman role? Black Knight actor? Cleese
Dict literal
cast = {input('role? '): input('actor? ')} role? Sir Robin actor? Eric Idle
The guaranteed execution order is helpful with assignment expressions because variables assigned in the key expression will be available in the value expression::
names = ['Martin von Löwis', 'Łukasz Langa', 'Walter Dörwald'] {(n := normalize('NFC', name)).casefold() : n for name in names} {'martin von löwis': 'Martin von Löwis', 'łukasz langa': 'Łukasz Langa', 'walter dörwald': 'Walter Dörwald'}
(Contributed by Jörn Heissler in :issue:35224.)
The :meth:object.__reduce__ method can now return a tuple from two to
six elements long. Formerly, five was the limit. The new, optional sixth
element is a callable with a (obj, state) signature. This allows the
direct control over the state-updating behavior of a specific object. If
not None, this callable will have priority over the object's
:meth:~object.__setstate__ method.
(Contributed by Pierre Glaser and Olivier Grisel in :issue:35900.)
The new :mod:importlib.metadata module provides (provisional) support for
reading metadata from third-party packages. For example, it can extract an
installed package's version number, list of entry points, and more::
Note following example requires that the popular "requests"
package has been installed.
from importlib.metadata import version, requires, files version('requests') '2.22.0' list(requires('requests')) ['chardet (<3.1.0,>=3.0.2)'] list(files('requests'))[:5] [PackagePath('requests-2.22.0.dist-info/INSTALLER'), PackagePath('requests-2.22.0.dist-info/LICENSE'), PackagePath('requests-2.22.0.dist-info/METADATA'), PackagePath('requests-2.22.0.dist-info/RECORD'), PackagePath('requests-2.22.0.dist-info/WHEEL')]
(Contributed by Barry Warsaw and Jason R. Coombs in :issue:34632.)
AST nodes now have end_lineno and end_col_offset attributes,
which give the precise location of the end of the node. (This only
applies to nodes that have lineno and col_offset attributes.)
New function :func:ast.get_source_segment returns the source code
for a specific AST node.
(Contributed by Ivan Levkivskyi in :issue:33416.)
The :func:ast.parse function has some new flags:
type_comments=True causes it to return the text of :pep:484 and
:pep:526 type comments associated with certain AST nodes;
mode='func_type' can be used to parse :pep:484 "signature type
comments" (returned for function definition AST nodes);
feature_version=(3, N) allows specifying an earlier Python 3
version. For example, feature_version=(3, 4) will treat
:keyword:async and :keyword:await as non-reserved words.
(Contributed by Guido van Rossum in :issue:35766.)
:func:asyncio.run has graduated from the provisional to stable API. This
function can be used to execute a :term:coroutine and return the result while
automatically managing the event loop. For example::
import asyncio
async def main():
await asyncio.sleep(0)
return 42
asyncio.run(main())
This is roughly equivalent to::
import asyncio
async def main():
await asyncio.sleep(0)
return 42
loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)
try:
loop.run_until_complete(main())
finally:
asyncio.set_event_loop(None)
loop.close()
The actual implementation is significantly more complex. Thus,
:func:asyncio.run should be the preferred way of running asyncio programs.
(Contributed by Yury Selivanov in :issue:32314.)
Running python -m asyncio launches a natively async REPL. This allows rapid
experimentation with code that has a top-level :keyword:await. There is no
longer a need to directly call asyncio.run() which would spawn a new event
loop on every invocation:
.. code-block:: none
$ python -m asyncio
asyncio REPL 3.8.0
Use "await" directly instead of "asyncio.run()".
Type "help", "copyright", "credits" or "license" for more information.
>>> import asyncio
>>> await asyncio.sleep(10, result='hello')
hello
(Contributed by Yury Selivanov in :issue:37028.)
The exception :class:asyncio.CancelledError now inherits from
:class:BaseException rather than :class:Exception and no longer inherits
from :class:concurrent.futures.CancelledError.
(Contributed by Yury Selivanov in :issue:32528.)
On Windows, the default event loop is now :class:~asyncio.ProactorEventLoop.
(Contributed by Victor Stinner in :issue:34687.)
:class:~asyncio.ProactorEventLoop now also supports UDP.
(Contributed by Adam Meily and Andrew Svetlov in :issue:29883.)
:class:~asyncio.ProactorEventLoop can now be interrupted by
:exc:KeyboardInterrupt ("CTRL+C").
(Contributed by Vladimir Matveev in :issue:23057.)
Added :meth:asyncio.Task.get_coro for getting the wrapped coroutine
within an :class:asyncio.Task.
(Contributed by Alex Grönholm in :issue:36999.)
Asyncio tasks can now be named, either by passing the name keyword
argument to :func:asyncio.create_task or
the :meth:~asyncio.loop.create_task event loop method, or by
calling the :meth:~asyncio.Task.set_name method on the task object. The
task name is visible in the repr() output of :class:asyncio.Task and
can also be retrieved using the :meth:~asyncio.Task.get_name method.
(Contributed by Alex Grönholm in :issue:34270.)
Added support for
Happy Eyeballs <https://en.wikipedia.org/wiki/Happy_Eyeballs>_ to
:func:asyncio.loop.create_connection. To specify the behavior, two new
parameters have been added: happy_eyeballs_delay and interleave. The Happy
Eyeballs algorithm improves responsiveness in applications that support IPv4
and IPv6 by attempting to simultaneously connect using both.
(Contributed by twisteroid ambassador in :issue:33530.)
The :func:compile built-in has been improved to accept the
ast.PyCF_ALLOW_TOP_LEVEL_AWAIT flag. With this new flag passed,
:func:compile will allow top-level await, async for and async with
constructs that are usually considered invalid syntax. Asynchronous code object
marked with the CO_COROUTINE flag may then be returned.
(Contributed by Matthias Bussonnier in :issue:34616)
The :meth:~collections.somenamedtuple._asdict method for
:func:collections.namedtuple now returns a :class:dict instead of a
:class:collections.OrderedDict. This works because regular dicts have
guaranteed ordering since Python 3.7. If the extra features of
:class:OrderedDict are required, the suggested remediation is to cast the
result to the desired type: OrderedDict(nt._asdict()).
(Contributed by Raymond Hettinger in :issue:35864.)
The :class:cProfile.Profile <profile.Profile> class can now be used as a context manager.
Profile a block of code by running::
import cProfile
with cProfile.Profile() as profiler:
# code to be profiled
...
(Contributed by Scott Sanderson in :issue:29235.)
The :class:csv.DictReader now returns instances of :class:dict instead of
a :class:collections.OrderedDict. The tool is now faster and uses less
memory while still preserving the field order.
(Contributed by Michael Selik in :issue:34003.)
Added a new variable holding structured version information for the
underlying ncurses library: :data:~curses.ncurses_version.
(Contributed by Serhiy Storchaka in :issue:31680.)
On Windows, :class:~ctypes.CDLL and subclasses now accept a winmode parameter
to specify flags for the underlying LoadLibraryEx call. The default flags are
set to only load DLL dependencies from trusted locations, including the path
where the DLL is stored (if a full or partial path is used to load the initial
DLL) and paths added by :func:~os.add_dll_directory.
(Contributed by Steve Dower in :issue:36085.)
Added new alternate constructors :meth:datetime.date.fromisocalendar and
:meth:datetime.datetime.fromisocalendar, which construct :class:~datetime.date and
:class:~datetime.datetime objects respectively from ISO year, week number, and weekday;
these are the inverse of each class's isocalendar method.
(Contributed by Paul Ganssle in :issue:36004.)
:func:functools.lru_cache can now be used as a straight decorator rather
than as a function returning a decorator. So both of these are now supported::
@lru_cache
def f(x):
...
@lru_cache(maxsize=256)
def f(x):
...
(Contributed by Raymond Hettinger in :issue:36772.)
Added a new :func:functools.cached_property decorator, for computed properties
cached for the life of the instance. ::
import functools import statistics
class Dataset: def init(self, sequence_of_numbers): self.data = sequence_of_numbers
@functools.cached_property
def variance(self):
return statistics.variance(self.data)
(Contributed by Carl Meyer in :issue:21145)
Added a new :func:functools.singledispatchmethod decorator that converts
methods into :term:generic functions <generic function> using
:term:single dispatch::
from functools import singledispatchmethod
from contextlib import suppress
class TaskManager:
def __init__(self, tasks):
self.tasks = list(tasks)
@singledispatchmethod
def discard(self, value):
with suppress(ValueError):
self.tasks.remove(value)
@discard.register(list)
def _(self, tasks):
targets = set(tasks)
self.tasks = [x for x in self.tasks if x not in targets]
(Contributed by Ethan Smith in :issue:32380)
:func:~gc.get_objects can now receive an optional generation parameter
indicating a generation to get objects from.
(Contributed by Pablo Galindo in :issue:36016.)
Added :func:~gettext.pgettext and its variants.
(Contributed by Franz Glasner, Éric Araujo, and Cheryl Sabella in :issue:2504.)
Added the mtime parameter to :func:gzip.compress for reproducible output.
(Contributed by Guo Ci Teo in :issue:34898.)
A :exc:~gzip.BadGzipFile exception is now raised instead of :exc:OSError
for certain types of invalid or corrupt gzip files.
(Contributed by Filip Gruszczyński, Michele Orrù, and Zackery Spytz in
:issue:6584.)
Output over N lines (50 by default) is squeezed down to a button.
N can be changed in the PyShell section of the General page of the
Settings dialog. Fewer, but possibly extra long, lines can be squeezed by
right clicking on the output. Squeezed output can be expanded in place
by double-clicking the button or into the clipboard or a separate window
by right-clicking the button. (Contributed by Tal Einat in :issue:1529353.)
Add "Run Customized" to the Run menu to run a module with customized
settings. Any command line arguments entered are added to sys.argv.
They also re-appear in the box for the next customized run. One can also
suppress the normal Shell main module restart. (Contributed by Cheryl
Sabella, Terry Jan Reedy, and others in :issue:5680 and :issue:37627.)
Added optional line numbers for IDLE editor windows. Windows
open without line numbers unless set otherwise in the General
tab of the configuration dialog. Line numbers for an existing
window are shown and hidden in the Options menu.
(Contributed by Tal Einat and Saimadhav Heblikar in :issue:17535.)
OS native encoding is now used for converting between Python strings and Tcl
objects. This allows IDLE to work with emoji and other non-BMP characters.
These characters can be displayed or copied and pasted to or from the
clipboard. Converting strings from Tcl to Python and back now never fails.
(Many people worked on this for eight years but the problem was finally
solved by Serhiy Storchaka in :issue:13153.)
New in 3.8.1:
Add option to toggle cursor blink off. (Contributed by Zackery Spytz
in :issue:4603.)
Escape key now closes IDLE completion windows. (Contributed by Johnny
Najera in :issue:38944.)
The changes above have been backported to 3.7 maintenance releases.
Add keywords to module name completion list. (Contributed by Terry J.
Reedy in :issue:37765.)
The :func:inspect.getdoc function can now find docstrings for __slots__
if that attribute is a :class:dict where the values are docstrings.
This provides documentation options similar to what we already have
for :func:property, :func:classmethod, and :func:staticmethod::
class AudioClip: slots = {'bit_rate': 'expressed in kilohertz to one decimal place', 'duration': 'in seconds, rounded up to an integer'} def init(self, bit_rate, duration): self.bit_rate = round(bit_rate / 1000.0, 1) self.duration = ceil(duration)
(Contributed by Raymond Hettinger in :issue:36326.)
In development mode (:option:-X env) and in :ref:debug build <debug-build>, the
:class:io.IOBase finalizer now logs the exception if the close() method
fails. The exception is ignored silently by default in release build.
(Contributed by Victor Stinner in :issue:18748.)
The :func:itertools.accumulate function added an option initial keyword
argument to specify an initial value::
>>> from itertools import accumulate
>>> list(accumulate([10, 5, 30, 15], initial=1000))
[1000, 1010, 1015, 1045, 1060]
(Contributed by Lisa Roach in :issue:34659.)
Add option --json-lines to parse every input line as a separate JSON object.
(Contributed by Weipeng Hong in :issue:31553.)
Added a force keyword argument to :func:logging.basicConfig.
When set to true, any existing handlers attached
to the root logger are removed and closed before carrying out the
configuration specified by the other arguments.
This solves a long-standing problem. Once a logger or basicConfig() had been called, subsequent calls to basicConfig() were silently ignored. This made it difficult to update, experiment with, or teach the various logging configuration options using the interactive prompt or a Jupyter notebook.
(Suggested by Raymond Hettinger, implemented by Donghee Na, and
reviewed by Vinay Sajip in :issue:33897.)
Added new function :func:math.dist for computing Euclidean distance
between two points. (Contributed by Raymond Hettinger in :issue:33089.)
Expanded the :func:math.hypot function to handle multiple dimensions.
Formerly, it only supported the 2-D case.
(Contributed by Raymond Hettinger in :issue:33089.)
Added new function, :func:math.prod, as analogous function to :func:sum
that returns the product of a 'start' value (default: 1) times an iterable of
numbers::
>>> prior = 0.8
>>> likelihoods = [0.625, 0.84, 0.30]
>>> math.prod(likelihoods, start=prior)
0.126
(Contributed by Pablo Galindo in :issue:35606.)
Added two new combinatoric functions :func:math.perm and :func:math.comb::
>>> math.perm(10, 3) # Permutations of 10 things taken 3 at a time
720
>>> math.comb(10, 3) # Combinations of 10 things taken 3 at a time
120
(Contributed by Yash Aggarwal, Keller Fuchs, Serhiy Storchaka, and Raymond
Hettinger in :issue:37128, :issue:37178, and :issue:35431.)
Added a new function :func:math.isqrt for computing accurate integer square
roots without conversion to floating point. The new function supports
arbitrarily large integers. It is faster than floor(sqrt(n)) but slower
than :func:math.sqrt::
>>> r = 650320427
>>> s = r ** 2
>>> isqrt(s - 1) # correct
650320426
>>> floor(sqrt(s - 1)) # incorrect
650320427
(Contributed by Mark Dickinson in :issue:36887.)
The function :func:math.factorial no longer accepts arguments that are not
int-like. (Contributed by Pablo Galindo in :issue:33083.)
The :class:mmap.mmap class now has an :meth:~mmap.mmap.madvise method to
access the madvise() system call.
(Contributed by Zackery Spytz in :issue:32941.)
Added new :mod:multiprocessing.shared_memory module.
(Contributed by Davin Potts in :issue:35813.)
On macOS, the spawn start method is now used by default.
(Contributed by Victor Stinner in :issue:33725.)
Added new function :func:~os.add_dll_directory on Windows for providing
additional search paths for native dependencies when importing extension
modules or loading DLLs using :mod:ctypes.
(Contributed by Steve Dower in :issue:36085.)
A new :func:os.memfd_create function was added to wrap the
memfd_create() syscall.
(Contributed by Zackery Spytz and Christian Heimes in :issue:26836.)
On Windows, much of the manual logic for handling reparse points (including
symlinks and directory junctions) has been delegated to the operating system.
Specifically, :func:os.stat will now traverse anything supported by the
operating system, while :func:os.lstat will only open reparse points that
identify as "name surrogates" while others are opened as for :func:os.stat.
In all cases, :attr:os.stat_result.st_mode will only have S_IFLNK set for
symbolic links and not other kinds of reparse points. To identify other kinds
of reparse point, check the new :attr:os.stat_result.st_reparse_tag attribute.
On Windows, :func:os.readlink is now able to read directory junctions. Note
that :func:~os.path.islink will return False for directory junctions,
and so code that checks islink first will continue to treat junctions as
directories, while code that handles errors from :func:os.readlink may now
treat junctions as links.
(Contributed by Steve Dower in :issue:37834.)
:mod:os.path functions that return a boolean result like
:func:~os.path.exists, :func:~os.path.lexists, :func:~os.path.isdir,
:func:~os.path.isfile, :func:~os.path.islink, and :func:~os.path.ismount
now return False instead of raising :exc:ValueError or its subclasses
:exc:UnicodeEncodeError and :exc:UnicodeDecodeError for paths that contain
characters or bytes unrepresentable at the OS level.
(Contributed by Serhiy Storchaka in :issue:33721.)
:func:~os.path.expanduser on Windows now prefers the :envvar:USERPROFILE
environment variable and does not use :envvar:HOME, which is not normally set
for regular user accounts.
(Contributed by Anthony Sottile in :issue:36264.)
:func:~os.path.isdir on Windows no longer returns True for a link to a
non-existent directory.
:func:~os.path.realpath on Windows now resolves reparse points, including
symlinks and directory junctions.
(Contributed by Steve Dower in :issue:37834.)
:mod:pathlib.Path methods that return a boolean result like
:meth:~pathlib.Path.exists, :meth:~pathlib.Path.is_dir,
:meth:~pathlib.Path.is_file, :meth:~pathlib.Path.is_mount,
:meth:~pathlib.Path.is_symlink, :meth:~pathlib.Path.is_block_device,
:meth:~pathlib.Path.is_char_device, :meth:~pathlib.Path.is_fifo,
:meth:~pathlib.Path.is_socket now return False instead of raising
:exc:ValueError or its subclass :exc:UnicodeEncodeError for paths that
contain characters unrepresentable at the OS level.
(Contributed by Serhiy Storchaka in :issue:33721.)
Added :meth:!pathlib.Path.link_to which creates a hard link pointing
to a path.
(Contributed by Joannah Nanjekye in :issue:26978)
Note that link_to was deprecated in 3.10 and removed in 3.12 in
favor of a hardlink_to method added in 3.10 which matches the
semantics of the existing symlink_to method.
:mod:pickle extensions subclassing the C-optimized :class:~pickle.Pickler
can now override the pickling logic of functions and classes by defining the
special :meth:~pickle.Pickler.reducer_override method.
(Contributed by Pierre Glaser and Olivier Grisel in :issue:35900.)
Added new :class:plistlib.UID and enabled support for reading and writing
NSKeyedArchiver-encoded binary plists.
(Contributed by Jon Janzen in :issue:26707.)
The :mod:pprint module added a sort_dicts parameter to several functions.
By default, those functions continue to sort dictionaries before rendering or
printing. However, if sort_dicts is set to false, the dictionaries retain
the order that keys were inserted. This can be useful for comparison to JSON
inputs during debugging.
In addition, there is a convenience new function, :func:pprint.pp that is
like :func:pprint.pprint but with sort_dicts defaulting to False::
>>> from pprint import pprint, pp
>>> d = dict(source='input.txt', operation='filter', destination='output.txt')
>>> pp(d, width=40) # Original order
{'source': 'input.txt',
'operation': 'filter',
'destination': 'output.txt'}
>>> pprint(d, width=40) # Keys sorted alphabetically
{'destination': 'output.txt',
'operation': 'filter',
'source': 'input.txt'}
(Contributed by Rémi Lapeyre in :issue:30670.)
:func:py_compile.compile now supports silent mode.
(Contributed by Joannah Nanjekye in :issue:22640.)
The new :func:shlex.join function acts as the inverse of :func:shlex.split.
(Contributed by Bo Bayles in :issue:32102.)
:func:shutil.copytree now accepts a new dirs_exist_ok keyword argument.
(Contributed by Josh Bronson in :issue:20849.)
:func:shutil.make_archive now defaults to the modern pax (POSIX.1-2001)
format for new archives to improve portability and standards conformance,
inherited from the corresponding change to the :mod:tarfile module.
(Contributed by C.A.M. Gerlach in :issue:30661.)
:func:shutil.rmtree on Windows now removes directory junctions without
recursively removing their contents first.
(Contributed by Steve Dower in :issue:37834.)
Added :meth:~socket.create_server and :meth:~socket.has_dualstack_ipv6
convenience functions to automate the necessary tasks usually involved when
creating a server socket, including accepting both IPv4 and IPv6 connections
on the same socket. (Contributed by Giampaolo Rodolà in :issue:17561.)
The :func:socket.if_nameindex, :func:socket.if_nametoindex, and
:func:socket.if_indextoname functions have been implemented on Windows.
(Contributed by Zackery Spytz in :issue:37007.)
Added :attr:~ssl.SSLContext.post_handshake_auth to enable and
:meth:~ssl.SSLSocket.verify_client_post_handshake to initiate TLS 1.3
post-handshake authentication.
(Contributed by Christian Heimes in :issue:34670.)
Added :func:statistics.fmean as a faster, floating-point variant of
:func:statistics.mean. (Contributed by Raymond Hettinger and
Steven D'Aprano in :issue:35904.)
Added :func:statistics.geometric_mean
(Contributed by Raymond Hettinger in :issue:27181.)
Added :func:statistics.multimode that returns a list of the most
common values. (Contributed by Raymond Hettinger in :issue:35892.)
Added :func:statistics.quantiles that divides data or a distribution
in to equiprobable intervals (e.g. quartiles, deciles, or percentiles).
(Contributed by Raymond Hettinger in :issue:36546.)
Added :class:statistics.NormalDist, a tool for creating
and manipulating normal distributions of a random variable.
(Contributed by Raymond Hettinger in :issue:36018.)
::
>>> temperature_feb = NormalDist.from_samples([4, 12, -3, 2, 7, 14])
>>> temperature_feb.mean
6.0
>>> temperature_feb.stdev
6.356099432828281
>>> temperature_feb.cdf(3) # Chance of being under 3 degrees
0.3184678262814532
>>> # Relative chance of being 7 degrees versus 10 degrees
>>> temperature_feb.pdf(7) / temperature_feb.pdf(10)
1.2039930378537762
>>> el_niño = NormalDist(4, 2.5)
>>> temperature_feb += el_niño # Add in a climate effect
>>> temperature_feb
NormalDist(mu=10.0, sigma=6.830080526611674)
>>> temperature_feb * (9/5) + 32 # Convert to Fahrenheit
NormalDist(mu=50.0, sigma=12.294144947901014)
>>> temperature_feb.samples(3) # Generate random samples
[7.672102882379219, 12.000027119750287, 4.647488369766392]
Add new :func:sys.unraisablehook function which can be overridden to control
how "unraisable exceptions" are handled. It is called when an exception has
occurred but there is no way for Python to handle it. For example, when a
destructor raises an exception or during garbage collection
(:func:gc.collect).
(Contributed by Victor Stinner in :issue:36829.)
The :mod:tarfile module now defaults to the modern pax (POSIX.1-2001)
format for new archives, instead of the previous GNU-specific one.
This improves cross-platform portability with a consistent encoding (UTF-8)
in a standardized and extensible format, and offers several other benefits.
(Contributed by C.A.M. Gerlach in :issue:36268.)
Add a new :func:threading.excepthook function which handles uncaught
:meth:threading.Thread.run exception. It can be overridden to control how
uncaught :meth:threading.Thread.run exceptions are handled.
(Contributed by Victor Stinner in :issue:1230540.)
Add a new :func:threading.get_native_id function and
a :data:~threading.Thread.native_id
attribute to the :class:threading.Thread class. These return the native
integral Thread ID of the current thread assigned by the kernel.
This feature is only available on certain platforms, see
:func:get_native_id <threading.get_native_id> for more information.
(Contributed by Jake Tesler in :issue:36084.)
The :mod:tokenize module now implicitly emits a NEWLINE token when
provided with input that does not have a trailing new line. This behavior
now matches what the C tokenizer does internally.
(Contributed by Ammar Askar in :issue:33899.)
Added methods :meth:!selection_from,
:meth:!selection_present,
:meth:!selection_range and
:meth:!selection_to
in the :class:!tkinter.Spinbox class.
(Contributed by Juliette Monsel in :issue:34829.)
Added method :meth:!moveto
in the :class:!tkinter.Canvas class.
(Contributed by Juliette Monsel in :issue:23831.)
The :class:!tkinter.PhotoImage class now has
:meth:!transparency_get and
:meth:!transparency_set methods. (Contributed by
Zackery Spytz in :issue:25451.)
Added new clock :const:~time.CLOCK_UPTIME_RAW for macOS 10.12.
(Contributed by Joannah Nanjekye in :issue:35702.)
The :mod:typing module incorporates several new features:
A dictionary type with per-key types. See :pep:589 and
:class:typing.TypedDict.
TypedDict uses only string keys. By default, every key is required
to be present. Specify "total=False" to allow keys to be optional::
class Location(TypedDict, total=False):
lat_long: tuple
grid_square: str
xy_coordinate: tuple
Literal types. See :pep:586 and :class:typing.Literal.
Literal types indicate that a parameter or return value
is constrained to one or more specific literal values::
def get_status(port: int) -> Literal['connected', 'disconnected']:
...
"Final" variables, functions, methods and classes. See :pep:591,
:class:typing.Final and :func:typing.final.
The final qualifier instructs a static type checker to restrict
subclassing, overriding, or reassignment::
pi: Final[float] = 3.1415926536
Protocol definitions. See :pep:544, :class:typing.Protocol and
:func:typing.runtime_checkable. Simple ABCs like
:class:typing.SupportsInt are now Protocol subclasses.
New protocol class :class:typing.SupportsIndex.
New functions :func:typing.get_origin and :func:typing.get_args.
The :mod:unicodedata module has been upgraded to use the Unicode 12.1.0 <https://blog.unicode.org/2019/05/unicode-12-1-en.html>_ release.
New function :func:~unicodedata.is_normalized can be used to verify a string
is in a specific normal form, often much faster than by actually normalizing
the string. (Contributed by Max Belanger, David Euresti, and Greg Price in
:issue:32285 and :issue:37966).
Added :class:~unittest.mock.AsyncMock to support an asynchronous version of
:class:~unittest.mock.Mock. Appropriate new assert functions for testing
have been added as well.
(Contributed by Lisa Roach in :issue:26467).
Added :func:~unittest.addModuleCleanup and
:meth:~unittest.TestCase.addClassCleanup to unittest to support
cleanups for :func:~unittest.setUpModule and
:meth:~unittest.TestCase.setUpClass.
(Contributed by Lisa Roach in :issue:24412.)
Several mock assert functions now also print a list of actual calls upon
failure. (Contributed by Petter Strandmark in :issue:35047.)
:mod:unittest module gained support for coroutines to be used as test cases
with :class:unittest.IsolatedAsyncioTestCase.
(Contributed by Andrew Svetlov in :issue:32972.)
Example::
import unittest
class TestRequest(unittest.IsolatedAsyncioTestCase):
async def asyncSetUp(self):
self.connection = await AsyncConnection()
async def test_get(self):
response = await self.connection.get("https://example.com")
self.assertEqual(response.status_code, 200)
async def asyncTearDown(self):
await self.connection.close()
if name == "main": unittest.main()
:mod:venv now includes an Activate.ps1 script on all platforms for
activating virtual environments under PowerShell Core 6.1.
(Contributed by Brett Cannon in :issue:32718.)
The proxy objects returned by :func:weakref.proxy now support the matrix
multiplication operators @ and @= in addition to the other
numeric operators. (Contributed by Mark Dickinson in :issue:36669.)
As mitigation against DTD and external entity retrieval, the
:mod:xml.dom.minidom and :mod:xml.sax modules no longer process
external entities by default.
(Contributed by Christian Heimes in :issue:17239.)
The .find*() methods in the :mod:xml.etree.ElementTree module
support wildcard searches like {*}tag which ignores the namespace
and {namespace}* which returns all tags in the given namespace.
(Contributed by Stefan Behnel in :issue:28238.)
The :mod:xml.etree.ElementTree module provides a new function
:func:~xml.etree.ElementTree.canonicalize that implements C14N 2.0.
(Contributed by Stefan Behnel in :issue:13611.)
The target object of :class:xml.etree.ElementTree.XMLParser can
receive namespace declaration events through the new callback methods
start_ns() and end_ns(). Additionally, the
:class:xml.etree.ElementTree.TreeBuilder target can be configured
to process events about comments and processing instructions to include
them in the generated tree.
(Contributed by Stefan Behnel in :issue:36676 and :issue:36673.)
:class:xmlrpc.client.ServerProxy now supports an optional headers keyword
argument for a sequence of HTTP headers to be sent with each request. Among
other things, this makes it possible to upgrade from default basic
authentication to faster session authentication.
(Contributed by Cédric Krier in :issue:35153.)
The :mod:subprocess module can now use the :func:os.posix_spawn function
in some cases for better performance. Currently, it is only used on macOS
and Linux (using glibc 2.24 or newer) if all these conditions are met:
(Contributed by Joannah Nanjekye and Victor Stinner in :issue:35537.)
:func:shutil.copyfile, :func:shutil.copy, :func:shutil.copy2,
:func:shutil.copytree and :func:shutil.move use platform-specific
"fast-copy" syscalls on Linux and macOS in order to copy the file
more efficiently.
"fast-copy" means that the copying operation occurs within the kernel,
avoiding the use of userspace buffers in Python as in
"outfd.write(infd.read())".
On Windows :func:shutil.copyfile uses a bigger default buffer size (1 MiB
instead of 16 KiB) and a :func:memoryview-based variant of
:func:shutil.copyfileobj is used.
The speedup for copying a 512 MiB file within the same partition is about
+26% on Linux, +50% on macOS and +40% on Windows. Also, much less CPU cycles
are consumed.
See :ref:shutil-platform-dependent-efficient-copy-operations section.
(Contributed by Giampaolo Rodolà in :issue:33671.)
:func:shutil.copytree uses :func:os.scandir function and all copy
functions depending from it use cached :func:os.stat values. The speedup
for copying a directory with 8000 files is around +9% on Linux, +20% on
Windows and +30% on a Windows SMB share. Also the number of :func:os.stat
syscalls is reduced by 38% making :func:shutil.copytree especially faster
on network filesystems. (Contributed by Giampaolo Rodolà in :issue:33695.)
The default protocol in the :mod:pickle module is now Protocol 4,
first introduced in Python 3.4. It offers better performance and smaller
size compared to Protocol 3 available since Python 3.0.
Removed one :c:type:Py_ssize_t member from PyGC_Head. All GC tracked
objects (e.g. tuple, list, dict) size is reduced 4 or 8 bytes.
(Contributed by Inada Naoki in :issue:33597.)
:class:uuid.UUID now uses __slots__ to reduce its memory footprint.
(Contributed by Wouter Bolsterlee and Tal Einat in :issue:30977)
Improved performance of :func:operator.itemgetter by 33%. Optimized
argument handling and added a fast path for the common case of a single
non-negative integer index into a tuple (which is the typical use case in
the standard library). (Contributed by Raymond Hettinger in
:issue:35664.)
Sped-up field lookups in :func:collections.namedtuple. They are now more
than two times faster, making them the fastest form of instance variable
lookup in Python. (Contributed by Raymond Hettinger, Pablo Galindo, and
Joe Jevnik, Serhiy Storchaka in :issue:32492.)
The :class:list constructor does not overallocate the internal item buffer
if the input iterable has a known length (the input implements __len__).
This makes the created list 12% smaller on average. (Contributed by
Raymond Hettinger and Pablo Galindo in :issue:33234.)
Doubled the speed of class variable writes. When a non-dunder attribute
was updated, there was an unnecessary call to update slots.
(Contributed by Stefan Behnel, Pablo Galindo Salgado, Raymond Hettinger,
Neil Schemenauer, and Serhiy Storchaka in :issue:36012.)
Reduced an overhead of converting arguments passed to many builtin functions
and methods. This sped up calling some simple builtin functions and
methods up to 20--50%. (Contributed by Serhiy Storchaka in :issue:23867,
:issue:35582 and :issue:36127.)
LOAD_GLOBAL instruction now uses new "per opcode cache" mechanism.
It is about 40% faster now. (Contributed by Yury Selivanov and Inada Naoki in
:issue:26219.)
Default :data:sys.abiflags became an empty string: the m flag for
pymalloc became useless (builds with and without pymalloc are ABI compatible)
and so has been removed. (Contributed by Victor Stinner in :issue:36707.)
Example of changes:
python3.8 program is installed, python3.8m program is gone.python3.8-config script is installed, python3.8m-config script
is gone.m flag has been removed from the suffix of dynamic library
filenames: extension modules in the standard library as well as those
produced and installed by third-party packages, like those downloaded from
PyPI. On Linux, for example, the Python 3.7 suffix
.cpython-37m-x86_64-linux-gnu.so became
.cpython-38-x86_64-linux-gnu.so in Python 3.8.The header files have been reorganized to better separate the different kinds of APIs:
Include/*.h should be the portable public stable C API.Include/cpython/*.h should be the unstable C API specific to CPython;
public API, with some private API prefixed by _Py or _PY.Include/internal/*.h is the private internal C API very specific to
CPython. This API comes with no backward compatibility warranty and should
not be used outside CPython. It is only exposed for very specific needs
like debuggers and profiles which has to access to CPython internals
without calling functions. This API is now installed by make install.(Contributed by Victor Stinner in :issue:35134 and :issue:35081,
work initiated by Eric Snow in Python 3.7.)
Some macros have been converted to static inline functions: parameter types and return type are well defined, they don't have issues specific to macros, variables have a local scopes. Examples:
Py_INCREF, :c:func:Py_DECREFPy_XINCREF, :c:func:Py_XDECREF!PyObject_INIT, :c:macro:!PyObject_INIT_VAR!_PyObject_GC_TRACK,
:c:func:!_PyObject_GC_UNTRACK, :c:func:!_Py_Dealloc(Contributed by Victor Stinner in :issue:35059.)
The :c:func:!PyByteArray_Init and :c:func:!PyByteArray_Fini functions have
been removed. They did nothing since Python 2.7.4 and Python 3.2.0, were
excluded from the limited API (stable ABI), and were not documented.
(Contributed by Victor Stinner in :issue:35713.)
The result of :c:func:PyExceptionClass_Name is now of type
const char * rather of char *.
(Contributed by Serhiy Storchaka in :issue:33818.)
The duality of Modules/Setup.dist and Modules/Setup has been
removed. Previously, when updating the CPython source tree, one had
to manually copy Modules/Setup.dist (inside the source tree) to
Modules/Setup (inside the build tree) in order to reflect any changes
upstream. This was of a small benefit to packagers at the expense of
a frequent annoyance to developers following CPython development, as
forgetting to copy the file could produce build failures.
Now the build system always reads from Modules/Setup inside the source
tree. People who want to customize that file are encouraged to maintain
their changes in a git fork of CPython or as patch files, as they would do
for any other change to the source tree.
(Contributed by Antoine Pitrou in :issue:32430.)
Functions that convert Python number to C integer like
:c:func:PyLong_AsLong and argument parsing functions like
:c:func:PyArg_ParseTuple with integer converting format units like 'i'
will now use the :meth:~object.__index__ special method instead of
:meth:~object.__int__, if available. The deprecation warning will be
emitted for objects with the __int__() method but without the
__index__() method (like :class:~decimal.Decimal and
:class:~fractions.Fraction). :c:func:PyNumber_Check will now return
1 for objects implementing __index__().
:c:func:PyNumber_Long, :c:func:PyNumber_Float and
:c:func:PyFloat_AsDouble also now use the __index__() method if
available.
(Contributed by Serhiy Storchaka in :issue:36048 and :issue:20092.)
Heap-allocated type objects will now increase their reference count
in :c:func:PyObject_Init (and its parallel macro PyObject_INIT)
instead of in :c:func:PyType_GenericAlloc. Types that modify instance
allocation or deallocation may need to be adjusted.
(Contributed by Eddie Elizondo in :issue:35810.)
The new function :c:func:!PyCode_NewWithPosOnlyArgs allows to create
code objects like :c:func:!PyCode_New, but with an extra posonlyargcount
parameter for indicating the number of positional-only arguments.
(Contributed by Pablo Galindo in :issue:37221.)
:c:func:!Py_SetPath now sets :data:sys.executable to the program full
path (:c:func:!Py_GetProgramFullPath) rather than to the program name
(:c:func:!Py_GetProgramName).
(Contributed by Victor Stinner in :issue:38234.)
The distutils bdist_wininst command is now deprecated, use
bdist_wheel (wheel packages) instead.
(Contributed by Victor Stinner in :issue:37481.)
Deprecated methods getchildren() and getiterator() in
the :mod:~xml.etree.ElementTree module now emit a
:exc:DeprecationWarning instead of :exc:PendingDeprecationWarning.
They will be removed in Python 3.9.
(Contributed by Serhiy Storchaka in :issue:29209.)
Passing an object that is not an instance of
:class:concurrent.futures.ThreadPoolExecutor to
:meth:loop.set_default_executor() <asyncio.loop.set_default_executor> is
deprecated and will be prohibited in Python 3.9.
(Contributed by Elvis Pranskevichus in :issue:34075.)
The :meth:~object.__getitem__ methods of :class:xml.dom.pulldom.DOMEventStream,
:class:wsgiref.util.FileWrapper and :class:fileinput.FileInput have been
deprecated.
Implementations of these methods have been ignoring their index parameter,
and returning the next item instead.
(Contributed by Berker Peksag in :issue:9372.)
The :class:typing.NamedTuple class has deprecated the _field_types
attribute in favor of the __annotations__ attribute which has the same
information. (Contributed by Raymond Hettinger in :issue:36320.)
:mod:ast classes Num, Str, Bytes, NameConstant and
Ellipsis are considered deprecated and will be removed in future Python
versions. :class:~ast.Constant should be used instead.
(Contributed by Serhiy Storchaka in :issue:32892.)
:class:ast.NodeVisitor methods visit_Num(), visit_Str(),
visit_Bytes(), visit_NameConstant() and visit_Ellipsis() are
deprecated now and will not be called in future Python versions.
Add the :meth:~ast.NodeVisitor.visit_Constant method to handle all
constant nodes.
(Contributed by Serhiy Storchaka in :issue:36917.)
The :deco:!asyncio.coroutine :term:decorator is deprecated and will be
removed in version 3.10. Instead of @asyncio.coroutine, use
:keyword:async def instead.
(Contributed by Andrew Svetlov in :issue:36921.)
In :mod:asyncio, the explicit passing of a loop argument has been
deprecated and will be removed in version 3.10 for the following:
:func:asyncio.sleep, :func:asyncio.gather, :func:asyncio.shield,
:func:asyncio.wait_for, :func:asyncio.wait, :func:asyncio.as_completed,
:class:asyncio.Task, :class:asyncio.Lock, :class:asyncio.Event,
:class:asyncio.Condition, :class:asyncio.Semaphore,
:class:asyncio.BoundedSemaphore, :class:asyncio.Queue,
:func:asyncio.create_subprocess_exec, and
:func:asyncio.create_subprocess_shell.
The explicit passing of coroutine objects to :func:asyncio.wait has been
deprecated and will be removed in version 3.11.
(Contributed by Yury Selivanov in :issue:34790.)
The following functions and methods are deprecated in the :mod:gettext
module: :func:!lgettext, :func:!ldgettext,
:func:!lngettext and :func:!ldngettext.
They return encoded bytes, and it's possible that you will get unexpected
Unicode-related exceptions if there are encoding problems with the
translated strings. It's much better to use alternatives which return
Unicode strings in Python 3. These functions have been broken for a long time.
Function :func:!bind_textdomain_codeset, methods
:meth:!NullTranslations.output_charset and
:meth:!NullTranslations.set_output_charset, and the codeset
parameter of functions :func:~gettext.translation and
:func:~gettext.install are also deprecated, since they are only used for
the l*gettext() functions.
(Contributed by Serhiy Storchaka in :issue:33710.)
The :meth:!isAlive method of :class:threading.Thread
has been deprecated.
(Contributed by Donghee Na in :issue:35283.)
Many builtin and extension functions that take integer arguments will
now emit a deprecation warning for :class:~decimal.Decimal\ s,
:class:~fractions.Fraction\ s and any other objects that can be converted
to integers only with a loss (e.g. that have the :meth:~object.__int__
method but do not have the :meth:~object.__index__ method). In future
version they will be errors.
(Contributed by Serhiy Storchaka in :issue:36048.)
Deprecated passing the following arguments as keyword arguments:
functools.partialmethod, :func:weakref.finalize,
:meth:profile.Profile.runcall, :meth:!cProfile.Profile.runcall,
:meth:bdb.Bdb.runcall, :meth:trace.Trace.runfunc and
:func:curses.wrapper.unittest.TestCase.addCleanup.~concurrent.futures.Executor.submit method of
:class:concurrent.futures.ThreadPoolExecutor and
:class:concurrent.futures.ProcessPoolExecutor.contextlib.ExitStack.callback,
:meth:!contextlib.AsyncExitStack.callback and
:meth:contextlib.AsyncExitStack.push_async_callback.!create
method of :class:!multiprocessing.managers.Server and
:class:!multiprocessing.managers.SharedMemoryServer.weakref.finalize.In future releases of Python, they will be :ref:positional-only <positional-only_parameter>.
(Contributed by Serhiy Storchaka in :issue:36492.)
The following features and APIs have been removed from Python 3.8:
Starting with Python 3.3, importing ABCs from :mod:collections was
deprecated, and importing should be done from :mod:collections.abc. Being
able to import from collections was marked for removal in 3.8, but has been
delayed to 3.9. (See :gh:81134.)
The :mod:!macpath module, deprecated in Python 3.7, has been removed.
(Contributed by Victor Stinner in :issue:35471.)
The function :func:!platform.popen has been removed, after having been
deprecated since Python 3.3: use :func:os.popen instead.
(Contributed by Victor Stinner in :issue:35345.)
The function :func:!time.clock has been removed, after having been
deprecated since Python 3.3: use :func:time.perf_counter or
:func:time.process_time instead, depending
on your requirements, to have well-defined behavior.
(Contributed by Matthias Bussonnier in :issue:36895.)
The pyvenv script has been removed in favor of python3.8 -m venv
to help eliminate confusion as to what Python interpreter the pyvenv
script is tied to. (Contributed by Brett Cannon in :issue:25427.)
parse_qs, parse_qsl, and escape are removed from the :mod:!cgi
module. They are deprecated in Python 3.2 or older. They should be imported
from the urllib.parse and html modules instead.
filemode function is removed from the :mod:tarfile module.
It is not documented and deprecated since Python 3.3.
The :class:~xml.etree.ElementTree.XMLParser constructor no longer accepts
the html argument. It never had an effect and was deprecated in Python 3.4.
All other parameters are now :ref:keyword-only <keyword-only_parameter>.
(Contributed by Serhiy Storchaka in :issue:29209.)
Removed the doctype() method of :class:~xml.etree.ElementTree.XMLParser.
(Contributed by Serhiy Storchaka in :issue:29209.)
"unicode_internal" codec is removed.
(Contributed by Inada Naoki in :issue:36297.)
The Cache and Statement objects of the :mod:sqlite3 module are not
exposed to the user.
(Contributed by Aviv Palivoda in :issue:30262.)
The bufsize keyword argument of :func:fileinput.input and
:func:fileinput.FileInput which was ignored and deprecated since Python 3.6
has been removed. :issue:36952 (Contributed by Matthias Bussonnier.)
The functions :func:!sys.set_coroutine_wrapper and
:func:!sys.get_coroutine_wrapper deprecated in Python 3.7 have been removed;
:issue:36933 (Contributed by Matthias Bussonnier.)
This section lists previously described changes and other bugfixes that may require changes to your code.
Yield expressions (both yield and yield from clauses) are now disallowed
in comprehensions and generator expressions (aside from the iterable expression
in the leftmost :keyword:!for clause).
(Contributed by Serhiy Storchaka in :issue:10544.)
The compiler now produces a :exc:SyntaxWarning when identity checks
(is and is not) are used with certain types of literals
(e.g. strings, numbers). These can often work by accident in CPython,
but are not guaranteed by the language spec. The warning advises users
to use equality tests (== and !=) instead.
(Contributed by Serhiy Storchaka in :issue:34850.)
The CPython interpreter can swallow exceptions in some circumstances.
In Python 3.8 this happens in fewer cases. In particular, exceptions
raised when getting the attribute from the type dictionary are no longer
ignored. (Contributed by Serhiy Storchaka in :issue:35459.)
Removed __str__ implementations from builtin types :class:bool,
:class:int, :class:float, :class:complex and few classes from
the standard library. They now inherit __str__() from :class:object.
As result, defining the __repr__() method in the subclass of these
classes will affect their string representation.
(Contributed by Serhiy Storchaka in :issue:36793.)
On AIX, :data:sys.platform doesn't contain the major version anymore.
It is always 'aix', instead of 'aix3' .. 'aix7'. Since
older Python versions include the version number, so it is recommended to
always use sys.platform.startswith('aix').
(Contributed by M. Felt in :issue:36588.)
:c:func:!PyEval_AcquireLock and :c:func:!PyEval_AcquireThread now
terminate the current thread if called while the interpreter is
finalizing, making them consistent with :c:func:PyEval_RestoreThread,
:c:func:Py_END_ALLOW_THREADS, and :c:func:PyGILState_Ensure. If this
behavior is not desired, guard the call by checking :c:func:!_Py_IsFinalizing
or :func:sys.is_finalizing.
(Contributed by Joannah Nanjekye in :issue:36475.)
The :func:os.getcwdb function now uses the UTF-8 encoding on Windows,
rather than the ANSI code page: see :pep:529 for the rationale. The
function is no longer deprecated on Windows.
(Contributed by Victor Stinner in :issue:37412.)
:class:subprocess.Popen can now use :func:os.posix_spawn in some cases
for better performance. On Windows Subsystem for Linux and QEMU User
Emulation, the :class:~subprocess.Popen constructor using
:func:os.posix_spawn no longer raises an exception on errors like
"missing program". Instead the child process fails with a
non-zero :attr:~subprocess.Popen.returncode.
(Contributed by Joannah Nanjekye and Victor Stinner in :issue:35537.)
The preexec_fn argument of * :class:subprocess.Popen is no longer
compatible with subinterpreters. The use of the parameter in a
subinterpreter now raises :exc:RuntimeError.
(Contributed by Eric Snow in :issue:34651, modified by Christian Heimes
in :issue:37951.)
The :meth:imaplib.IMAP4.logout method no longer silently ignores arbitrary
exceptions.
(Contributed by Victor Stinner in :issue:36348.)
The function :func:!platform.popen has been removed, after having been deprecated since
Python 3.3: use :func:os.popen instead.
(Contributed by Victor Stinner in :issue:35345.)
The :func:statistics.mode function no longer raises an exception
when given multimodal data. Instead, it returns the first mode
encountered in the input data. (Contributed by Raymond Hettinger
in :issue:35892.)
The :meth:~tkinter.ttk.Treeview.selection method of the
:class:tkinter.ttk.Treeview class no longer takes arguments. Using it with
arguments for changing the selection was deprecated in Python 3.6. Use
specialized methods like :meth:~tkinter.ttk.Treeview.selection_set for
changing the selection. (Contributed by Serhiy Storchaka in :issue:31508.)
The :meth:~xml.dom.minidom.Node.writexml, :meth:~xml.dom.minidom.Node.toxml
and :meth:~xml.dom.minidom.Node.toprettyxml methods of
:mod:xml.dom.minidom and the :meth:~xml.etree.ElementTree.ElementTree.write
method of :mod:xml.etree.ElementTree now preserve the attribute order
specified by the user.
(Contributed by Diego Rojas and Raymond Hettinger in :issue:34160.)
A :mod:dbm.dumb database opened with flags 'r' is now read-only.
:func:dbm.dumb.open with flags 'r' and 'w' no longer creates
a database if it does not exist.
(Contributed by Serhiy Storchaka in :issue:32749.)
The doctype() method defined in a subclass of
:class:~xml.etree.ElementTree.XMLParser will no longer be called and will
emit a :exc:RuntimeWarning instead of a :exc:DeprecationWarning.
Define the :meth:doctype() <xml.etree.ElementTree.TreeBuilder.doctype>
method on a target for handling an XML doctype declaration.
(Contributed by Serhiy Storchaka in :issue:29209.)
A :exc:RuntimeError is now raised when the custom metaclass doesn't
provide the __classcell__ entry in the namespace passed to
type.__new__. A :exc:DeprecationWarning was emitted in Python
3.6--3.7. (Contributed by Serhiy Storchaka in :issue:23722.)
The :class:cProfile.Profile <profile.Profile> class can now be used as
a context manager. (Contributed by Scott Sanderson in :issue:29235.)
:func:shutil.copyfile, :func:shutil.copy, :func:shutil.copy2,
:func:shutil.copytree and :func:shutil.move use platform-specific
"fast-copy" syscalls (see
:ref:shutil-platform-dependent-efficient-copy-operations section).
:func:shutil.copyfile default buffer size on Windows was changed from
16 KiB to 1 MiB.
The PyGC_Head struct has changed completely. All code that touched the
struct member should be rewritten. (See :issue:33597.)
The :c:type:PyInterpreterState struct has been moved into the "internal"
header files (specifically Include/internal/pycore_pystate.h). An
opaque PyInterpreterState is still available as part of the public
API (and stable ABI). The docs indicate that none of the struct's
fields are public, so we hope no one has been using them. However,
if you do rely on one or more of those private fields and have no
alternative then please open a BPO issue. We'll work on helping
you adjust (possibly including adding accessor functions to the
public API). (See :issue:35886.)
The :meth:mmap.flush() <mmap.mmap.flush> method now returns None on
success and raises an exception on error under all platforms. Previously,
its behavior was platform-dependent: a nonzero value was returned on success;
zero was returned on error under Windows. A zero value was returned on
success; an exception was raised on error under Unix.
(Contributed by Berker Peksag in :issue:2122.)
:mod:xml.dom.minidom and :mod:xml.sax modules no longer process
external entities by default.
(Contributed by Christian Heimes in :issue:17239.)
Deleting a key from a read-only :mod:dbm database (:mod:dbm.dumb,
:mod:dbm.gnu or :mod:dbm.ndbm) raises :attr:!error (:exc:dbm.dumb.error,
:exc:dbm.gnu.error or :exc:dbm.ndbm.error) instead of :exc:KeyError.
(Contributed by Xiang Zhang in :issue:33106.)
Simplified AST for literals. All constants will be represented as
:class:ast.Constant instances. Instantiating old classes Num,
Str, Bytes, NameConstant and Ellipsis will return
an instance of Constant.
(Contributed by Serhiy Storchaka in :issue:32892.)
:func:~os.path.expanduser on Windows now prefers the :envvar:USERPROFILE
environment variable and does not use :envvar:HOME, which is not normally
set for regular user accounts.
(Contributed by Anthony Sottile in :issue:36264.)
The exception :class:asyncio.CancelledError now inherits from
:class:BaseException rather than :class:Exception and no longer inherits
from :class:concurrent.futures.CancelledError.
(Contributed by Yury Selivanov in :issue:32528.)
The function :func:asyncio.wait_for now correctly waits for cancellation
when using an instance of :class:asyncio.Task. Previously, upon reaching
timeout, it was cancelled and immediately returned.
(Contributed by Elvis Pranskevichus in :issue:32751.)
The function :func:asyncio.BaseTransport.get_extra_info now returns a safe
to use socket object when 'socket' is passed to the name parameter.
(Contributed by Yury Selivanov in :issue:37027.)
:class:asyncio.BufferedProtocol has graduated to the stable API.
.. _bpo-36085-whatsnew:
DLL dependencies for extension modules and DLLs loaded with :mod:ctypes on
Windows are now resolved more securely. Only the system paths, the directory
containing the DLL or PYD file, and directories added with
:func:~os.add_dll_directory are searched for load-time dependencies.
Specifically, :envvar:PATH and the current working directory are no longer
used, and modifications to these will no longer have any effect on normal DLL
resolution. If your application relies on these mechanisms, you should check
for :func:~os.add_dll_directory and if it exists, use it to add your DLLs
directory while loading your library. Note that Windows 7 users will need to
ensure that Windows Update KB2533623 has been installed (this is also verified
by the installer).
(Contributed by Steve Dower in :issue:36085.)
The header files and functions related to pgen have been removed after its
replacement by a pure Python implementation. (Contributed by Pablo Galindo
in :issue:36623.)
:class:types.CodeType has a new parameter in the second position of the
constructor (posonlyargcount) to support positional-only arguments defined
in :pep:570. The first argument (argcount) now represents the total
number of positional arguments (including positional-only arguments). The new
replace() method of :class:types.CodeType can be used to make the code
future-proof.
The parameter digestmod for :func:hmac.new no longer uses the MD5 digest
by default.
The :c:struct:PyCompilerFlags structure got a new cf_feature_version
field. It should be initialized to PY_MINOR_VERSION. The field is ignored
by default, and is used if and only if PyCF_ONLY_AST flag is set in
cf_flags.
(Contributed by Guido van Rossum in :issue:35766.)
The :c:func:!PyEval_ReInitThreads function has been removed from the C API.
It should not be called explicitly: use :c:func:PyOS_AfterFork_Child
instead.
(Contributed by Victor Stinner in :issue:36728.)
On Unix, C extensions are no longer linked to libpython except on Android
and Cygwin. When Python is embedded, libpython must not be loaded with
RTLD_LOCAL, but RTLD_GLOBAL instead. Previously, using
RTLD_LOCAL, it was already not possible to load C extensions which
were not linked to libpython, like C extensions of the standard
library built by the *shared* section of Modules/Setup.
(Contributed by Victor Stinner in :issue:21536.)
Use of # variants of formats in parsing or building value (e.g.
:c:func:PyArg_ParseTuple, :c:func:Py_BuildValue, :c:func:PyObject_CallFunction,
etc.) without PY_SSIZE_T_CLEAN defined raises DeprecationWarning now.
It will be removed in 3.10 or 4.0. Read :ref:arg-parsing for detail.
(Contributed by Inada Naoki in :issue:36381.)
Instances of heap-allocated types (such as those created with
:c:func:PyType_FromSpec) hold a reference to their type object.
Increasing the reference count of these type objects has been moved from
:c:func:PyType_GenericAlloc to the more low-level functions,
:c:func:PyObject_Init and :c:macro:!PyObject_INIT.
This makes types created through :c:func:PyType_FromSpec behave like
other classes in managed code.
:ref:Statically allocated types <static-types> are not affected.
For the vast majority of cases, there should be no side effect. However, types that manually increase the reference count after allocating an instance (perhaps to work around the bug) may now become immortal. To avoid this, these classes need to call Py_DECREF on the type object during instance deallocation.
To correctly port these types into 3.8, please apply the following changes:
Remove :c:macro:Py_INCREF on the type object after allocating an
instance - if any.
This may happen after calling :c:macro:PyObject_New,
:c:macro:PyObject_NewVar, :c:func:PyObject_GC_New,
:c:func:PyObject_GC_NewVar, or any other custom allocator that uses
:c:func:PyObject_Init or :c:macro:!PyObject_INIT.
Example:
.. code-block:: c
static foo_struct *
foo_new(PyObject *type) {
foo_struct *foo = PyObject_GC_New(foo_struct, (PyTypeObject *) type);
if (foo == NULL)
return NULL;
#if PY_VERSION_HEX < 0x03080000
// Workaround for Python issue 35810; no longer necessary in Python 3.8
PY_INCREF(type)
#endif
return foo;
}
Ensure that all custom tp_dealloc functions of heap-allocated types
decrease the type's reference count.
Example:
.. code-block:: c
static void
foo_dealloc(foo_struct *instance) {
PyObject *type = Py_TYPE(instance);
PyObject_GC_Del(instance);
#if PY_VERSION_HEX >= 0x03080000
// This was not needed before Python 3.8 (Python issue 35810)
Py_DECREF(type);
#endif
}
(Contributed by Eddie Elizondo in :issue:35810.)
The :c:macro:Py_DEPRECATED() macro has been implemented for MSVC.
The macro now must be placed before the symbol name.
Example:
.. code-block:: c
Py_DEPRECATED(3.8) PyAPI_FUNC(int) Py_OldFunction(void);
(Contributed by Zackery Spytz in :issue:33407.)
The interpreter does not pretend to support binary compatibility of
extension types across feature releases, anymore. A :c:type:PyTypeObject
exported by a third-party extension module is supposed to have all the
slots expected in the current Python version, including
:c:member:~PyTypeObject.tp_finalize (:c:macro:Py_TPFLAGS_HAVE_FINALIZE
is not checked anymore before reading :c:member:~PyTypeObject.tp_finalize).
(Contributed by Antoine Pitrou in :issue:32388.)
The functions :c:func:!PyNode_AddChild and :c:func:!PyParser_AddToken now accept
two additional int arguments end_lineno and end_col_offset.
The :file:libpython38.a file to allow MinGW tools to link directly against
:file:python38.dll is no longer included in the regular Windows distribution.
If you require this file, it may be generated with the gendef and
dlltool tools, which are part of the MinGW binutils package:
.. code-block:: shell
gendef - python38.dll > tmp.def
dlltool --dllname python38.dll --def tmp.def --output-lib libpython38.a
The location of an installed :file:pythonXY.dll will depend on the
installation options and the version and language of Windows. See
:ref:using-on-windows for more information. The resulting library should be
placed in the same directory as :file:pythonXY.lib, which is generally the
:file:libs directory under your Python installation.
(Contributed by Steve Dower in :issue:37351.)
The interpreter loop has been simplified by moving the logic of unrolling
the stack of blocks into the compiler. The compiler emits now explicit
instructions for adjusting the stack of values and calling the
cleaning-up code for :keyword:break, :keyword:continue and
:keyword:return.
Removed opcodes :opcode:!BREAK_LOOP, :opcode:!CONTINUE_LOOP,
:opcode:!SETUP_LOOP and :opcode:!SETUP_EXCEPT. Added new opcodes
:opcode:!ROT_FOUR, :opcode:!BEGIN_FINALLY, :opcode:!CALL_FINALLY and
:opcode:!POP_FINALLY. Changed the behavior of :opcode:!END_FINALLY
and :opcode:!WITH_CLEANUP_START.
(Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka in
:issue:17611.)
Added new opcode :opcode:END_ASYNC_FOR for handling exceptions raised
when awaiting a next item in an :keyword:async for loop.
(Contributed by Serhiy Storchaka in :issue:33041.)
The :opcode:MAP_ADD now expects the value as the first element in the
stack and the key as the second element. This change was made so the key
is always evaluated before the value in dictionary comprehensions, as
proposed by :pep:572. (Contributed by Jörn Heissler in :issue:35224.)
Added a benchmark script for timing various ways to access variables:
Tools/scripts/var_access_benchmark.py.
(Contributed by Raymond Hettinger in :issue:35884.)
Here's a summary of performance improvements since Python 3.3:
.. code-block:: none
Python version 3.3 3.4 3.5 3.6 3.7 3.8
-------------- --- --- --- --- --- ---
Variable and attribute read access:
read_local 4.0 7.1 7.1 5.4 5.1 3.9
read_nonlocal 5.3 7.1 8.1 5.8 5.4 4.4
read_global 13.3 15.5 19.0 14.3 13.6 7.6
read_builtin 20.0 21.1 21.6 18.5 19.0 7.5
read_classvar_from_class 20.5 25.6 26.5 20.7 19.5 18.4
read_classvar_from_instance 18.5 22.8 23.5 18.8 17.1 16.4
read_instancevar 26.8 32.4 33.1 28.0 26.3 25.4
read_instancevar_slots 23.7 27.8 31.3 20.8 20.8 20.2
read_namedtuple 68.5 73.8 57.5 45.0 46.8 18.4
read_boundmethod 29.8 37.6 37.9 29.6 26.9 27.7
Variable and attribute write access:
write_local 4.6 8.7 9.3 5.5 5.3 4.3
write_nonlocal 7.3 10.5 11.1 5.6 5.5 4.7
write_global 15.9 19.7 21.2 18.0 18.0 15.8
write_classvar 81.9 92.9 96.0 104.6 102.1 39.2
write_instancevar 36.4 44.6 45.8 40.0 38.9 35.5
write_instancevar_slots 28.7 35.6 36.1 27.3 26.6 25.7
Data structure read access:
read_list 19.2 24.2 24.5 20.8 20.8 19.0
read_deque 19.9 24.7 25.5 20.2 20.6 19.8
read_dict 19.7 24.3 25.7 22.3 23.0 21.0
read_strdict 17.9 22.6 24.3 19.5 21.2 18.9
Data structure write access:
write_list 21.2 27.1 28.5 22.5 21.6 20.0
write_deque 23.8 28.7 30.1 22.7 21.8 23.5
write_dict 25.9 31.4 33.3 29.3 29.2 24.7
write_strdict 22.9 28.4 29.9 27.5 25.2 23.1
Stack (or queue) operations:
list_append_pop 144.2 93.4 112.7 75.4 74.2 50.8
deque_append_pop 30.4 43.5 57.0 49.4 49.2 42.5
deque_append_popleft 30.8 43.7 57.3 49.7 49.7 42.8
Timing loop:
loop_overhead 0.3 0.5 0.6 0.4 0.3 0.3
The benchmarks were measured on an
Intel® Core™ i7-4960HQ processor <https://ark.intel.com/content/www/us/en/ark/products/76088/intel-core-i7-4960hq-processor-6m-cache-up-to-3-80-ghz.html>_
running the macOS 64-bit builds found at
python.org <https://www.python.org/downloads/macos/>_.
The benchmark script displays timings in nanoseconds.
Due to significant security concerns, the reuse_address parameter of
:meth:asyncio.loop.create_datagram_endpoint is no longer supported. This is
because of the behavior of the socket option SO_REUSEADDR in UDP. For more
details, see the documentation for loop.create_datagram_endpoint().
(Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in
:issue:37228.)
Fixed a regression with the ignore callback of :func:shutil.copytree.
The argument types are now str and List[str] again.
(Contributed by Manuel Barkhau and Giampaolo Rodola in :gh:83571.)
The constant values of future flags in the :mod:__future__ module
are updated in order to prevent collision with compiler flags. Previously
PyCF_ALLOW_TOP_LEVEL_AWAIT was clashing with CO_FUTURE_DIVISION.
(Contributed by Batuhan Taskaya in :gh:83743)
Earlier Python versions allowed using both ; and & as
query parameter separators in :func:urllib.parse.parse_qs and
:func:urllib.parse.parse_qsl. Due to security concerns, and to conform with
newer W3C recommendations, this has been changed to allow only a single
separator key, with & as the default. This change also affects
:func:!cgi.parse and :func:!cgi.parse_multipart as they use the affected
functions internally. For more details, please see their respective
documentation.
(Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in :issue:42967.)
A security fix alters the :class:ftplib.FTP behavior to not trust the
IPv4 address sent from the remote server when setting up a passive data
channel. We reuse the ftp server IP address instead. For unusual code
requiring the old behavior, set a trust_server_pasv_ipv4_address
attribute on your FTP instance to True. (See :gh:87451)
As of 3.8.10, Python now supports building and running on macOS 11
(Big Sur) and on Apple Silicon Macs (based on the ARM64 architecture).
A new universal build variant, universal2, is now available to natively
support both ARM64 and Intel 64 in one set of executables.
Note that support for "weaklinking", building binaries targeted for newer
versions of macOS that will also run correctly on older versions by
testing at runtime for missing features, is not included in this backport
from Python 3.9; to support a range of macOS versions, continue to target
for and build on the oldest version in the range.
(Originally contributed by Ronald Oussoren and Lawrence D'Anna in :gh:85272,
with fixes by FX Coudert and Eli Rykoff, and backported to 3.8 by Maxime Bélanger
and Ned Deily)
The presence of newline or tab characters in parts of a URL allows for some
forms of attacks. Following the WHATWG specification that updates :rfc:3986,
ASCII newline \n, \r and tab \t characters are stripped from the
URL by the parser in :mod:urllib.parse preventing such attacks. The removal
characters are controlled by a new module level variable
urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE. (See :issue:43882)
Starting with Python 3.8.12 the :mod:ipaddress module no longer accepts
any leading zeros in IPv4 address strings. Leading zeros are ambiguous and
interpreted as octal notation by some libraries. For example the legacy
function :func:socket.inet_aton treats leading zeros as octal notation.
glibc implementation of modern :func:~socket.inet_pton does not accept
any leading zeros.
(Originally contributed by Christian Heimes in :issue:36384, and backported
to 3.8 by Achraf Merzouki.)
Converting between :class:int and :class:str in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal)
now raises a :exc:ValueError if the number of digits in string form is
above a limit to avoid potential denial of service attacks due to the
algorithmic complexity. This is a mitigation for :cve:2020-10735.
This limit can be configured or disabled by environment variable, command
line flag, or :mod:sys APIs. See the :ref:integer string conversion length limitation <int_max_str_digits> documentation. The default limit
is 4300 digits in string form.
tarfile, and :func:shutil.unpack_archive,
have a new a filter argument that allows limiting tar features than may be
surprising or dangerous, such as creating files outside the destination
directory.
See :ref:tarfile-extraction-filter for details.
In Python 3.12, use without the filter argument will show a
:exc:DeprecationWarning.
In Python 3.14, the default will switch to 'data'.
(Contributed by Petr Viktorin in :pep:706.)