What’s New In Python 3.8

What’s New In Python 3.8¶
- 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 changelog.
Summary – Release highlights¶
New Features¶
Assignment expressions¶
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.
In this example, the assignment expression helps avoid calling
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:
# Loop over fixed length blocks
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 bpo-35224.)
Positional-only parameters¶
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 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 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 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 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 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 bpo-36540.)
Parallel filesystem cache for compiled bytecode files¶
The new PYTHONPYCACHEPREFIX
setting (also available as
-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 sys.pycache_prefix
(None
indicates the default location in __pycache__
subdirectories).
(Contributed by Carl Meyer in bpo-33499.)
Debug build uses the same ABI as release build¶
Python now uses the same ABI whether it’s built in release or debug mode. 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.
Release builds and debug builds are now ABI compatible: 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 sys.getobjects()
function and the PYTHONDUMPREFS
environment variable, can be set using the new ./configure
--with-trace-refs
build option.
(Contributed by Victor Stinner in bpo-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 bpo-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 bpo-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 bpo-36721.)
f-strings support =
for self-documenting expressions and debugging¶
Added an =
specifier to f-strings. 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:
>>> user = 'eric_idle'
>>> member_since = date(1975, 7, 31)
>>> f'{user=} {member_since=}'
"user='eric_idle' member_since=datetime.date(1975, 7, 31)"
The usual f-string format specifiers allow more control over how the result of the expression is displayed:
>>> delta = 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 bpo-36817.)
PEP 578: Python Runtime Audit Hooks¶
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.
PEP 587: Python Initialization Configuration¶
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:
New functions:
This PEP also adds _PyRuntimeState.preconfig
(PyPreConfig
type)
and PyInterpreterState.config
(PyConfig
type) fields to these
internal structures. PyInterpreterState.config
becomes the new
reference configuration, replacing global configuration variables and
other private variables.
See Python Initialization Configuration for the documentation.
See PEP 587 for a full description.
(Contributed by Victor Stinner in bpo-36763.)
PEP 590: Vectorcall: a fast calling protocol for CPython¶
The Vectorcall Protocol is added to the Python/C API. It is meant to formalize existing optimizations which were already done for various classes. Any static type 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 bpo-36974.)
Pickle protocol 5 with out-of-band data buffers¶
When 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 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 bpo-36785.)
Other Language Changes¶
A
continue
statement was illegal in thefinally
clause due to a problem with the implementation. In Python 3.8 this restriction was lifted. (Contributed by Serhiy Storchaka in bpo-32489.)The
bool
,int
, andfractions.Fraction
types now have anas_integer_ratio()
method like that found infloat
anddecimal.Decimal
. This minor API extension makes it possible to writenumerator, denominator = x.as_integer_ratio()
and have it work across multiple numeric types. (Contributed by Lisa Roach in bpo-33073 and Raymond Hettinger in bpo-37819.)Constructors of
int
,float
andcomplex
will now use the__index__()
special method, if available and the corresponding method__int__()
,__float__()
or__complex__()
is not available. (Contributed by Serhiy Storchaka in bpo-20092.)Added support of
\N{name}
escapes inregular expressions
:>>> 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 bpo-30688.)
Dict and dictviews are now iterable in reversed insertion order using
reversed()
. (Contributed by Rémi Lapeyre in bpo-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 bpo-34641.)Generalized iterable unpacking in
yield
andreturn
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 bpo-32117.)
When a comma is missed in code such as
[(10, 20) (30, 40)]
, the compiler displays aSyntaxWarning
with a helpful suggestion. This improves on just having aTypeError
indicating that the first tuple was not callable. (Contributed by Serhiy Storchaka in bpo-15248.)Arithmetic operations between subclasses of
datetime.date
ordatetime.datetime
anddatetime.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) usesdatetime.timedelta
arithmetic, such asastimezone()
. (Contributed by Paul Ganssle in bpo-32417.)When the Python interpreter is interrupted by Ctrl-C (SIGINT) and the resulting
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 bpo-1054041.)Some advanced styles of programming require updating the
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 newreplace()
method makes it possible to create a clone with a few altered parameters.Here’s an example that alters the
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 bpo-37032.)
For integers, the three-argument form of the
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 of 38 modulo 137, write:>>> pow(38, -1, 137) 119 >>> 119 * 38 % 137 1
Modular inverses arise in the solution of linear Diophantine equations. For example, to find integer solutions for
4258𝑥 + 147𝑦 = 369
, first rewrite as4258𝑥 ≡ 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 bpo-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 bpo-35224.)
The
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__setstate__()
method. (Contributed by Pierre Glaser and Olivier Grisel in bpo-35900.)
New Modules¶
The new
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 bpo-34632.)
Improved Modules¶
ast¶
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 ast.get_source_segment()
returns the source code
for a specific AST node.
(Contributed by Ivan Levkivskyi in bpo-33416.)
The 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 treatasync
andawait
as non-reserved words.
(Contributed by Guido van Rossum in bpo-35766.)
asyncio¶
asyncio.run()
has graduated from the provisional to stable API. This
function can be used to execute a 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,
asyncio.run()
should be the preferred way of running asyncio programs.
(Contributed by Yury Selivanov in bpo-32314.)
Running python -m asyncio
launches a natively async REPL. This allows rapid
experimentation with code that has a top-level await
. There is no
longer a need to directly call asyncio.run()
which would spawn a new event
loop on every invocation:
$ 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 bpo-37028.)
The exception asyncio.CancelledError
now inherits from
BaseException
rather than Exception
and no longer inherits
from concurrent.futures.CancelledError
.
(Contributed by Yury Selivanov in bpo-32528.)
On Windows, the default event loop is now ProactorEventLoop
.
(Contributed by Victor Stinner in bpo-34687.)
ProactorEventLoop
now also supports UDP.
(Contributed by Adam Meily and Andrew Svetlov in bpo-29883.)
ProactorEventLoop
can now be interrupted by
KeyboardInterrupt
(“CTRL+C”).
(Contributed by Vladimir Matveev in bpo-23057.)
Added asyncio.Task.get_coro()
for getting the wrapped coroutine
within an asyncio.Task
.
(Contributed by Alex Grönholm in bpo-36999.)
Asyncio tasks can now be named, either by passing the name
keyword
argument to asyncio.create_task()
or
the create_task()
event loop method, or by
calling the set_name()
method on the task object. The
task name is visible in the repr()
output of asyncio.Task
and
can also be retrieved using the get_name()
method.
(Contributed by Alex Grönholm in bpo-34270.)
Added support for
Happy Eyeballs to
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 bpo-33530.)
builtins¶
The compile()
built-in has been improved to accept the
ast.PyCF_ALLOW_TOP_LEVEL_AWAIT
flag. With this new flag passed,
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 bpo-34616)
collections¶
The _asdict()
method for
collections.namedtuple()
now returns a dict
instead of a
collections.OrderedDict
. This works because regular dicts have
guaranteed ordering since Python 3.7. If the extra features of
OrderedDict
are required, the suggested remediation is to cast the
result to the desired type: OrderedDict(nt._asdict())
.
(Contributed by Raymond Hettinger in bpo-35864.)
cProfile¶
The cProfile.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 bpo-29235.)
csv¶
The csv.DictReader
now returns instances of dict
instead of
a collections.OrderedDict
. The tool is now faster and uses less
memory while still preserving the field order.
(Contributed by Michael Selik in bpo-34003.)
curses¶
Added a new variable holding structured version information for the
underlying ncurses library: ncurses_version
.
(Contributed by Serhiy Storchaka in bpo-31680.)
ctypes¶
On Windows, 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 add_dll_directory()
.
(Contributed by Steve Dower in bpo-36085.)
datetime¶
Added new alternate constructors datetime.date.fromisocalendar()
and
datetime.datetime.fromisocalendar()
, which construct date
and
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 bpo-36004.)
functools¶
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 bpo-36772.)
Added a new 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 bpo-21145)
Added a new functools.singledispatchmethod()
decorator that converts
methods into generic functions using
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 bpo-32380)
gc¶
get_objects()
can now receive an optional generation parameter
indicating a generation to get objects from.
(Contributed by Pablo Galindo in bpo-36016.)
gettext¶
Added pgettext()
and its variants.
(Contributed by Franz Glasner, Éric Araujo, and Cheryl Sabella in bpo-2504.)
gzip¶
Added the mtime parameter to gzip.compress()
for reproducible output.
(Contributed by Guo Ci Teo in bpo-34898.)
A BadGzipFile
exception is now raised instead of OSError
for certain types of invalid or corrupt gzip files.
(Contributed by Filip Gruszczyński, Michele Orrù, and Zackery Spytz in
bpo-6584.)
IDLE and idlelib¶
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 bpo-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 bpo-5680 and bpo-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 bpo-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 bpo-13153.)
New in 3.8.1:
Add option to toggle cursor blink off. (Contributed by Zackery Spytz in bpo-4603.)
Escape key now closes IDLE completion windows. (Contributed by Johnny Najera in bpo-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 bpo-37765.)
inspect¶
The inspect.getdoc()
function can now find docstrings for __slots__
if that attribute is a dict
where the values are docstrings.
This provides documentation options similar to what we already have
for property()
, classmethod()
, and 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 bpo-36326.)
io¶
In development mode (-X
env
) and in debug build, the
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 bpo-18748.)
itertools¶
The 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 bpo-34659.)
json.tool¶
Add option --json-lines
to parse every input line as a separate JSON object.
(Contributed by Weipeng Hong in bpo-31553.)
logging¶
Added a force keyword argument to 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 bpo-33897.)
math¶
Added new function math.dist()
for computing Euclidean distance
between two points. (Contributed by Raymond Hettinger in bpo-33089.)
Expanded the math.hypot()
function to handle multiple dimensions.
Formerly, it only supported the 2-D case.
(Contributed by Raymond Hettinger in bpo-33089.)
Added new function, math.prod()
, as analogous function to 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 bpo-35606.)
Added two new combinatoric functions math.perm()
and 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 bpo-37128, bpo-37178, and bpo-35431.)
Added a new function 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 math.sqrt()
:
>>> r = 650320427
>>> s = r ** 2
>>> isqrt(s - 1) # correct
650320426
>>> floor(sqrt(s - 1)) # incorrect
650320427
(Contributed by Mark Dickinson in bpo-36887.)
The function math.factorial()
no longer accepts arguments that are not
int-like. (Contributed by Pablo Galindo in bpo-33083.)
mmap¶
The mmap.mmap
class now has an madvise()
method to
access the madvise()
system call.
(Contributed by Zackery Spytz in bpo-32941.)
multiprocessing¶
Added new multiprocessing.shared_memory
module.
(Contributed by Davin Potts in bpo-35813.)
On macOS, the spawn start method is now used by default. (Contributed by Victor Stinner in bpo-33725.)
os¶
Added new function add_dll_directory()
on Windows for providing
additional search paths for native dependencies when importing extension
modules or loading DLLs using ctypes
.
(Contributed by Steve Dower in bpo-36085.)
A new os.memfd_create()
function was added to wrap the
memfd_create()
syscall.
(Contributed by Zackery Spytz and Christian Heimes in bpo-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, os.stat()
will now traverse anything supported by the
operating system, while os.lstat()
will only open reparse points that
identify as “name surrogates” while others are opened as for os.stat()
.
In all cases, 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 os.stat_result.st_reparse_tag
attribute.
On Windows, os.readlink()
is now able to read directory junctions. Note
that 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 os.readlink()
may now
treat junctions as links.
(Contributed by Steve Dower in bpo-37834.)
os.path¶
os.path
functions that return a boolean result like
exists()
, lexists()
, isdir()
,
isfile()
, islink()
, and ismount()
now return False
instead of raising ValueError
or its subclasses
UnicodeEncodeError
and UnicodeDecodeError
for paths that contain
characters or bytes unrepresentable at the OS level.
(Contributed by Serhiy Storchaka in bpo-33721.)
expanduser()
on Windows now prefers the USERPROFILE
environment variable and does not use HOME
, which is not normally set
for regular user accounts.
(Contributed by Anthony Sottile in bpo-36264.)
isdir()
on Windows no longer returns True
for a link to a
non-existent directory.
realpath()
on Windows now resolves reparse points, including
symlinks and directory junctions.
(Contributed by Steve Dower in bpo-37834.)
pathlib¶
pathlib.Path
methods that return a boolean result like
exists()
, is_dir()
,
is_file()
, is_mount()
,
is_symlink()
, is_block_device()
,
is_char_device()
, is_fifo()
,
is_socket()
now return False
instead of raising
ValueError
or its subclass UnicodeEncodeError
for paths that
contain characters unrepresentable at the OS level.
(Contributed by Serhiy Storchaka in bpo-33721.)
Added pathlib.Path.link_to()
which creates a hard link pointing
to a path.
(Contributed by Joannah Nanjekye in bpo-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.
pickle¶
pickle
extensions subclassing the C-optimized Pickler
can now override the pickling logic of functions and classes by defining the
special reducer_override()
method.
(Contributed by Pierre Glaser and Olivier Grisel in bpo-35900.)
plistlib¶
Added new plistlib.UID
and enabled support for reading and writing
NSKeyedArchiver-encoded binary plists.
(Contributed by Jon Janzen in bpo-26707.)
pprint¶
The 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, pprint.pp()
that is
like 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 bpo-30670.)
py_compile¶
py_compile.compile()
now supports silent mode.
(Contributed by Joannah Nanjekye in bpo-22640.)
shlex¶
The new shlex.join()
function acts as the inverse of shlex.split()
.
(Contributed by Bo Bayles in bpo-32102.)
shutil¶
shutil.copytree()
now accepts a new dirs_exist_ok
keyword argument.
(Contributed by Josh Bronson in bpo-20849.)
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 tarfile
module.
(Contributed by C.A.M. Gerlach in bpo-30661.)
shutil.rmtree()
on Windows now removes directory junctions without
recursively removing their contents first.
(Contributed by Steve Dower in bpo-37834.)
socket¶
Added create_server()
and 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 bpo-17561.)
The socket.if_nameindex()
, socket.if_nametoindex()
, and
socket.if_indextoname()
functions have been implemented on Windows.
(Contributed by Zackery Spytz in bpo-37007.)
ssl¶
Added post_handshake_auth
to enable and
verify_client_post_handshake()
to initiate TLS 1.3
post-handshake authentication.
(Contributed by Christian Heimes in bpo-34670.)
statistics¶
Added statistics.fmean()
as a faster, floating-point variant of
statistics.mean()
. (Contributed by Raymond Hettinger and
Steven D’Aprano in bpo-35904.)
Added statistics.geometric_mean()
(Contributed by Raymond Hettinger in bpo-27181.)
Added statistics.multimode()
that returns a list of the most
common values. (Contributed by Raymond Hettinger in bpo-35892.)
Added statistics.quantiles()
that divides data or a distribution
in to equiprobable intervals (e.g. quartiles, deciles, or percentiles).
(Contributed by Raymond Hettinger in bpo-36546.)
Added statistics.NormalDist
, a tool for creating
and manipulating normal distributions of a random variable.
(Contributed by Raymond Hettinger in bpo-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]
sys¶
Add new 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
(gc.collect()
).
(Contributed by Victor Stinner in bpo-36829.)
tarfile¶
The 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 bpo-36268.)
threading¶
Add a new threading.excepthook()
function which handles uncaught
threading.Thread.run()
exception. It can be overridden to control how
uncaught threading.Thread.run()
exceptions are handled.
(Contributed by Victor Stinner in bpo-1230540.)
Add a new threading.get_native_id()
function and
a native_id
attribute to the 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
get_native_id
for more information.
(Contributed by Jake Tesler in bpo-36084.)
tokenize¶
The 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 bpo-33899.)
tkinter¶
Added methods selection_from()
,
selection_present()
,
selection_range()
and
selection_to()
in the tkinter.Spinbox
class.
(Contributed by Juliette Monsel in bpo-34829.)
Added method moveto()
in the tkinter.Canvas
class.
(Contributed by Juliette Monsel in bpo-23831.)
The tkinter.PhotoImage
class now has
transparency_get()
and
transparency_set()
methods. (Contributed by
Zackery Spytz in bpo-25451.)
time¶
Added new clock CLOCK_UPTIME_RAW
for macOS 10.12.
(Contributed by Joannah Nanjekye in bpo-35702.)
typing¶
The typing
module incorporates several new features:
A dictionary type with per-key types. See PEP 589 and
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
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,
typing.Final
andtyping.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,
typing.Protocol
andtyping.runtime_checkable()
. Simple ABCs liketyping.SupportsInt
are nowProtocol
subclasses.New protocol class
typing.SupportsIndex
.New functions
typing.get_origin()
andtyping.get_args()
.
unicodedata¶
The unicodedata
module has been upgraded to use the Unicode 12.1.0 release.
New function 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
bpo-32285 and bpo-37966).
unittest¶
Added AsyncMock
to support an asynchronous version of
Mock
. Appropriate new assert functions for testing
have been added as well.
(Contributed by Lisa Roach in bpo-26467).
Added addModuleCleanup()
and
addClassCleanup()
to unittest to support
cleanups for setUpModule()
and
setUpClass()
.
(Contributed by Lisa Roach in bpo-24412.)
Several mock assert functions now also print a list of actual calls upon failure. (Contributed by Petter Strandmark in bpo-35047.)
unittest
module gained support for coroutines to be used as test cases
with unittest.IsolatedAsyncioTestCase
.
(Contributed by Andrew Svetlov in bpo-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()
venv¶
venv
now includes an Activate.ps1
script on all platforms for
activating virtual environments under PowerShell Core 6.1.
(Contributed by Brett Cannon in bpo-32718.)
weakref¶
The proxy objects returned by weakref.proxy()
now support the matrix
multiplication operators @
and @=
in addition to the other
numeric operators. (Contributed by Mark Dickinson in bpo-36669.)
xml¶
As mitigation against DTD and external entity retrieval, the
xml.dom.minidom
and xml.sax
modules no longer process
external entities by default.
(Contributed by Christian Heimes in bpo-17239.)
The .find*()
methods in the 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 bpo-28238.)
The xml.etree.ElementTree
module provides a new function
canonicalize()
that implements C14N 2.0.
(Contributed by Stefan Behnel in bpo-13611.)
The target object of xml.etree.ElementTree.XMLParser
can
receive namespace declaration events through the new callback methods
start_ns()
and end_ns()
. Additionally, the
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 bpo-36676 and bpo-36673.)
xmlrpc¶
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 bpo-35153.)
Optimizations¶
The
subprocess
module can now use theos.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:close_fds is false;
preexec_fn, pass_fds, cwd and start_new_session parameters are not set;
the executable path contains a directory.
(Contributed by Joannah Nanjekye and Victor Stinner in bpo-35537.)
shutil.copyfile()
,shutil.copy()
,shutil.copy2()
,shutil.copytree()
andshutil.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 Windowsshutil.copyfile()
uses a bigger default buffer size (1 MiB instead of 16 KiB) and amemoryview()
-based variant ofshutil.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 Platform-dependent efficient copy operations section. (Contributed by Giampaolo Rodolà in bpo-33671.)shutil.copytree()
usesos.scandir()
function and all copy functions depending from it use cachedos.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 ofos.stat()
syscalls is reduced by 38% makingshutil.copytree()
especially faster on network filesystems. (Contributed by Giampaolo Rodolà in bpo-33695.)The default protocol in the
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
Py_ssize_t
member fromPyGC_Head
. All GC tracked objects (e.g. tuple, list, dict) size is reduced 4 or 8 bytes. (Contributed by Inada Naoki in bpo-33597.)uuid.UUID
now uses__slots__
to reduce its memory footprint. (Contributed by Wouter Bolsterlee and Tal Einat in bpo-30977)Improved performance of
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 bpo-35664.)Sped-up field lookups in
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 bpo-32492.)The
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 bpo-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 bpo-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 bpo-23867, bpo-35582 and bpo-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 bpo-26219.)
Build and C API Changes¶
Default
sys.abiflags
became an empty string: them
flag for pymalloc became useless (builds with and without pymalloc are ABI compatible) and so has been removed. (Contributed by Victor Stinner in bpo-36707.)Example of changes:
Only
python3.8
program is installed,python3.8m
program is gone.Only
python3.8-config
script is installed,python3.8m-config
script is gone.The
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 bymake install
.
(Contributed by Victor Stinner in bpo-35134 and bpo-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:
PyObject_INIT
,PyObject_INIT_VAR
Private functions:
_PyObject_GC_TRACK()
,_PyObject_GC_UNTRACK()
,_Py_Dealloc()
(Contributed by Victor Stinner in bpo-35059.)
The
PyByteArray_Init()
andPyByteArray_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 bpo-35713.)The result of
PyExceptionClass_Name()
is now of typeconst char *
rather ofchar *
. (Contributed by Serhiy Storchaka in bpo-33818.)The duality of
Modules/Setup.dist
andModules/Setup
has been removed. Previously, when updating the CPython source tree, one had to manually copyModules/Setup.dist
(inside the source tree) toModules/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 bpo-32430.)
Functions that convert Python number to C integer like
PyLong_AsLong()
and argument parsing functions likePyArg_ParseTuple()
with integer converting format units like'i'
will now use the__index__()
special method instead of__int__()
, if available. The deprecation warning will be emitted for objects with the__int__()
method but without the__index__()
method (likeDecimal
andFraction
).PyNumber_Check()
will now return1
for objects implementing__index__()
.PyNumber_Long()
,PyNumber_Float()
andPyFloat_AsDouble()
also now use the__index__()
method if available. (Contributed by Serhiy Storchaka in bpo-36048 and bpo-20092.)Heap-allocated type objects will now increase their reference count in
PyObject_Init()
(and its parallel macroPyObject_INIT
) instead of inPyType_GenericAlloc()
. Types that modify instance allocation or deallocation may need to be adjusted. (Contributed by Eddie Elizondo in bpo-35810.)The new function
PyCode_NewWithPosOnlyArgs()
allows to create code objects likePyCode_New()
, but with an extra posonlyargcount parameter for indicating the number of positional-only arguments. (Contributed by Pablo Galindo in bpo-37221.)Py_SetPath()
now setssys.executable
to the program full path (Py_GetProgramFullPath()
) rather than to the program name (Py_GetProgramName()
). (Contributed by Victor Stinner in bpo-38234.)
Deprecated¶
The distutils
bdist_wininst
command is now deprecated, usebdist_wheel
(wheel packages) instead. (Contributed by Victor Stinner in bpo-37481.)Deprecated methods
getchildren()
andgetiterator()
in theElementTree
module now emit aDeprecationWarning
instead ofPendingDeprecationWarning
. They will be removed in Python 3.9. (Contributed by Serhiy Storchaka in bpo-29209.)Passing an object that is not an instance of
concurrent.futures.ThreadPoolExecutor
toloop.set_default_executor()
is deprecated and will be prohibited in Python 3.9. (Contributed by Elvis Pranskevichus in bpo-34075.)The
__getitem__()
methods ofxml.dom.pulldom.DOMEventStream
,wsgiref.util.FileWrapper
andfileinput.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 bpo-9372.)
The
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 bpo-36320.)ast
classesNum
,Str
,Bytes
,NameConstant
andEllipsis
are considered deprecated and will be removed in future Python versions.Constant
should be used instead. (Contributed by Serhiy Storchaka in bpo-32892.)ast.NodeVisitor
methodsvisit_Num()
,visit_Str()
,visit_Bytes()
,visit_NameConstant()
andvisit_Ellipsis()
are deprecated now and will not be called in future Python versions. Add thevisit_Constant()
method to handle all constant nodes. (Contributed by Serhiy Storchaka in bpo-36917.)The
@asyncio.coroutine
decorator is deprecated and will be removed in version 3.10. Instead of@asyncio.coroutine
, useasync def
instead. (Contributed by Andrew Svetlov in bpo-36921.)In
asyncio
, the explicit passing of a loop argument has been deprecated and will be removed in version 3.10 for the following:asyncio.sleep()
,asyncio.gather()
,asyncio.shield()
,asyncio.wait_for()
,asyncio.wait()
,asyncio.as_completed()
,asyncio.Task
,asyncio.Lock
,asyncio.Event
,asyncio.Condition
,asyncio.Semaphore
,asyncio.BoundedSemaphore
,asyncio.Queue
,asyncio.create_subprocess_exec()
, andasyncio.create_subprocess_shell()
.The explicit passing of coroutine objects to
asyncio.wait()
has been deprecated and will be removed in version 3.11. (Contributed by Yury Selivanov in bpo-34790.)The following functions and methods are deprecated in the
gettext
module:lgettext()
,ldgettext()
,lngettext()
andldngettext()
. 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
bind_textdomain_codeset()
, methodsNullTranslations.output_charset()
andNullTranslations.set_output_charset()
, and the codeset parameter of functionstranslation()
andinstall()
are also deprecated, since they are only used for thel*gettext()
functions. (Contributed by Serhiy Storchaka in bpo-33710.)The
isAlive()
method ofthreading.Thread
has been deprecated. (Contributed by Donghee Na in bpo-35283.)Many builtin and extension functions that take integer arguments will now emit a deprecation warning for
Decimal
s,Fraction
s and any other objects that can be converted to integers only with a loss (e.g. that have the__int__()
method but do not have the__index__()
method). In future version they will be errors. (Contributed by Serhiy Storchaka in bpo-36048.)Deprecated passing the following arguments as keyword arguments:
func in
functools.partialmethod()
,weakref.finalize()
,profile.Profile.runcall()
,cProfile.Profile.runcall()
,bdb.Bdb.runcall()
,trace.Trace.runfunc()
andcurses.wrapper()
.function in
unittest.TestCase.addCleanup()
.fn in the
submit()
method ofconcurrent.futures.ThreadPoolExecutor
andconcurrent.futures.ProcessPoolExecutor
.callback in
contextlib.ExitStack.callback()
,contextlib.AsyncExitStack.callback()
andcontextlib.AsyncExitStack.push_async_callback()
.c and typeid in the
create()
method ofmultiprocessing.managers.Server
andmultiprocessing.managers.SharedMemoryServer
.obj in
weakref.finalize()
.
In future releases of Python, they will be positional-only. (Contributed by Serhiy Storchaka in bpo-36492.)
API and Feature Removals¶
The following features and APIs have been removed from Python 3.8:
Starting with Python 3.3, importing ABCs from
collections
was deprecated, and importing should be done fromcollections.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
macpath
module, deprecated in Python 3.7, has been removed. (Contributed by Victor Stinner in bpo-35471.)The function
platform.popen()
has been removed, after having been deprecated since Python 3.3: useos.popen()
instead. (Contributed by Victor Stinner in bpo-35345.)The function
time.clock()
has been removed, after having been deprecated since Python 3.3: usetime.perf_counter()
ortime.process_time()
instead, depending on your requirements, to have well-defined behavior. (Contributed by Matthias Bussonnier in bpo-36895.)The
pyvenv
script has been removed in favor ofpython3.8 -m venv
to help eliminate confusion as to what Python interpreter thepyvenv
script is tied to. (Contributed by Brett Cannon in bpo-25427.)parse_qs
,parse_qsl
, andescape
are removed from thecgi
module. They are deprecated in Python 3.2 or older. They should be imported from theurllib.parse
andhtml
modules instead.filemode
function is removed from thetarfile
module. It is not documented and deprecated since Python 3.3.The
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 keyword-only. (Contributed by Serhiy Storchaka in bpo-29209.)Removed the
doctype()
method ofXMLParser
. (Contributed by Serhiy Storchaka in bpo-29209.)“unicode_internal” codec is removed. (Contributed by Inada Naoki in bpo-36297.)
The
Cache
andStatement
objects of thesqlite3
module are not exposed to the user. (Contributed by Aviv Palivoda in bpo-30262.)The
bufsize
keyword argument offileinput.input()
andfileinput.FileInput()
which was ignored and deprecated since Python 3.6 has been removed. bpo-36952 (Contributed by Matthias Bussonnier.)The functions
sys.set_coroutine_wrapper()
andsys.get_coroutine_wrapper()
deprecated in Python 3.7 have been removed; bpo-36933 (Contributed by Matthias Bussonnier.)
Porting to Python 3.8¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Changes in Python behavior¶
Yield expressions (both
yield
andyield from
clauses) are now disallowed in comprehensions and generator expressions (aside from the iterable expression in the leftmostfor
clause). (Contributed by Serhiy Storchaka in bpo-10544.)The compiler now produces a
SyntaxWarning
when identity checks (is
andis 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 bpo-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 bpo-35459.)
Removed
__str__
implementations from builtin typesbool
,int
,float
,complex
and few classes from the standard library. They now inherit__str__()
fromobject
. As result, defining the__repr__()
method in the subclass of these classes will affect their string representation. (Contributed by Serhiy Storchaka in bpo-36793.)On AIX,
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 usesys.platform.startswith('aix')
. (Contributed by M. Felt in bpo-36588.)PyEval_AcquireLock()
andPyEval_AcquireThread()
now terminate the current thread if called while the interpreter is finalizing, making them consistent withPyEval_RestoreThread()
,Py_END_ALLOW_THREADS()
, andPyGILState_Ensure()
. If this behavior is not desired, guard the call by checking_Py_IsFinalizing()
orsys.is_finalizing()
. (Contributed by Joannah Nanjekye in bpo-36475.)
Changes in the Python API¶
The
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 bpo-37412.)subprocess.Popen
can now useos.posix_spawn()
in some cases for better performance. On Windows Subsystem for Linux and QEMU User Emulation, thePopen
constructor usingos.posix_spawn()
no longer raises an exception on errors like “missing program”. Instead the child process fails with a non-zeroreturncode
. (Contributed by Joannah Nanjekye and Victor Stinner in bpo-35537.)The preexec_fn argument of *
subprocess.Popen
is no longer compatible with subinterpreters. The use of the parameter in a subinterpreter now raisesRuntimeError
. (Contributed by Eric Snow in bpo-34651, modified by Christian Heimes in bpo-37951.)The
imaplib.IMAP4.logout()
method no longer silently ignores arbitrary exceptions. (Contributed by Victor Stinner in bpo-36348.)The function
platform.popen()
has been removed, after having been deprecated since Python 3.3: useos.popen()
instead. (Contributed by Victor Stinner in bpo-35345.)The
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 bpo-35892.)The
selection()
method of thetkinter.ttk.Treeview
class no longer takes arguments. Using it with arguments for changing the selection was deprecated in Python 3.6. Use specialized methods likeselection_set()
for changing the selection. (Contributed by Serhiy Storchaka in bpo-31508.)The
writexml()
,toxml()
andtoprettyxml()
methods ofxml.dom.minidom
and thewrite()
method ofxml.etree.ElementTree
now preserve the attribute order specified by the user. (Contributed by Diego Rojas and Raymond Hettinger in bpo-34160.)A
dbm.dumb
database opened with flags'r'
is now read-only.dbm.dumb.open()
with flags'r'
and'w'
no longer creates a database if it does not exist. (Contributed by Serhiy Storchaka in bpo-32749.)The
doctype()
method defined in a subclass ofXMLParser
will no longer be called and will emit aRuntimeWarning
instead of aDeprecationWarning
. Define thedoctype()
method on a target for handling an XML doctype declaration. (Contributed by Serhiy Storchaka in bpo-29209.)A
RuntimeError
is now raised when the custom metaclass doesn’t provide the__classcell__
entry in the namespace passed totype.__new__
. ADeprecationWarning
was emitted in Python 3.6–3.7. (Contributed by Serhiy Storchaka in bpo-23722.)The
cProfile.Profile
class can now be used as a context manager. (Contributed by Scott Sanderson in bpo-29235.)shutil.copyfile()
,shutil.copy()
,shutil.copy2()
,shutil.copytree()
andshutil.move()
use platform-specific “fast-copy” syscalls (see Platform-dependent efficient copy operations section).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 bpo-33597.)The
PyInterpreterState
struct has been moved into the “internal” header files (specifically Include/internal/pycore_pystate.h). An opaquePyInterpreterState
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 bpo-35886.)The
mmap.flush()
method now returnsNone
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 bpo-2122.)xml.dom.minidom
andxml.sax
modules no longer process external entities by default. (Contributed by Christian Heimes in bpo-17239.)Deleting a key from a read-only
dbm
database (dbm.dumb
,dbm.gnu
ordbm.ndbm
) raiseserror
(dbm.dumb.error
,dbm.gnu.error
ordbm.ndbm.error
) instead ofKeyError
. (Contributed by Xiang Zhang in bpo-33106.)Simplified AST for literals. All constants will be represented as
ast.Constant
instances. Instantiating old classesNum
,Str
,Bytes
,NameConstant
andEllipsis
will return an instance ofConstant
. (Contributed by Serhiy Storchaka in bpo-32892.)expanduser()
on Windows now prefers theUSERPROFILE
environment variable and does not useHOME
, which is not normally set for regular user accounts. (Contributed by Anthony Sottile in bpo-36264.)The exception
asyncio.CancelledError
now inherits fromBaseException
rather thanException
and no longer inherits fromconcurrent.futures.CancelledError
. (Contributed by Yury Selivanov in bpo-32528.)The function
asyncio.wait_for()
now correctly waits for cancellation when using an instance ofasyncio.Task
. Previously, upon reaching timeout, it was cancelled and immediately returned. (Contributed by Elvis Pranskevichus in bpo-32751.)The function
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 bpo-37027.)asyncio.BufferedProtocol
has graduated to the stable API.
DLL dependencies for extension modules and DLLs loaded with
ctypes
on Windows are now resolved more securely. Only the system paths, the directory containing the DLL or PYD file, and directories added withadd_dll_directory()
are searched for load-time dependencies. Specifically,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 foradd_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 bpo-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 bpo-36623.)
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 newreplace()
method oftypes.CodeType
can be used to make the code future-proof.The parameter
digestmod
forhmac.new()
no longer uses the MD5 digest by default.
Changes in the C API¶
The
PyCompilerFlags
structure got a new cf_feature_version field. It should be initialized toPY_MINOR_VERSION
. The field is ignored by default, and is used if and only ifPyCF_ONLY_AST
flag is set in cf_flags. (Contributed by Guido van Rossum in bpo-35766.)The
PyEval_ReInitThreads()
function has been removed from the C API. It should not be called explicitly: usePyOS_AfterFork_Child()
instead. (Contributed by Victor Stinner in bpo-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 withRTLD_LOCAL
, butRTLD_GLOBAL
instead. Previously, usingRTLD_LOCAL
, it was already not possible to load C extensions which were not linked tolibpython
, like C extensions of the standard library built by the*shared*
section ofModules/Setup
. (Contributed by Victor Stinner in bpo-21536.)Use of
#
variants of formats in parsing or building value (e.g.PyArg_ParseTuple()
,Py_BuildValue()
,PyObject_CallFunction()
, etc.) withoutPY_SSIZE_T_CLEAN
defined raisesDeprecationWarning
now. It will be removed in 3.10 or 4.0. Read Parsing arguments and building values for detail. (Contributed by Inada Naoki in bpo-36381.)Instances of heap-allocated types (such as those created with
PyType_FromSpec()
) hold a reference to their type object. Increasing the reference count of these type objects has been moved fromPyType_GenericAlloc()
to the more low-level functions,PyObject_Init()
andPyObject_INIT
. This makes types created throughPyType_FromSpec()
behave like other classes in managed code.Statically allocated 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
Py_INCREF
on the type object after allocating an instance - if any. This may happen after callingPyObject_New
,PyObject_NewVar
,PyObject_GC_New()
,PyObject_GC_NewVar()
, or any other custom allocator that usesPyObject_Init()
orPyObject_INIT
.Example:
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:
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 bpo-35810.)
The
Py_DEPRECATED()
macro has been implemented for MSVC. The macro now must be placed before the symbol name.Example:
Py_DEPRECATED(3.8) PyAPI_FUNC(int) Py_OldFunction(void);
(Contributed by Zackery Spytz in bpo-33407.)
The interpreter does not pretend to support binary compatibility of extension types across feature releases, anymore. A
PyTypeObject
exported by a third-party extension module is supposed to have all the slots expected in the current Python version, includingtp_finalize
(Py_TPFLAGS_HAVE_FINALIZE
is not checked anymore before readingtp_finalize
).(Contributed by Antoine Pitrou in bpo-32388.)
The functions
PyNode_AddChild()
andPyParser_AddToken()
now accept two additionalint
arguments end_lineno and end_col_offset.The
libpython38.a
file to allow MinGW tools to link directly againstpython38.dll
is no longer included in the regular Windows distribution. If you require this file, it may be generated with thegendef
anddlltool
tools, which are part of the MinGW binutils package:gendef - python38.dll > tmp.def dlltool --dllname python38.dll --def tmp.def --output-lib libpython38.a
The location of an installed
pythonXY.dll
will depend on the installation options and the version and language of Windows. See Using Python on Windows for more information. The resulting library should be placed in the same directory aspythonXY.lib
, which is generally thelibs
directory under your Python installation.(Contributed by Steve Dower in bpo-37351.)
CPython bytecode changes¶
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
break
,continue
andreturn
.Removed opcodes
BREAK_LOOP
,CONTINUE_LOOP
,SETUP_LOOP
andSETUP_EXCEPT
. Added new opcodesROT_FOUR
,BEGIN_FINALLY
,CALL_FINALLY
andPOP_FINALLY
. Changed the behavior ofEND_FINALLY
andWITH_CLEANUP_START
.(Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka in bpo-17611.)
Added new opcode
END_ASYNC_FOR
for handling exceptions raised when awaiting a next item in anasync for
loop. (Contributed by Serhiy Storchaka in bpo-33041.)The
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 bpo-35224.)
Demos and Tools¶
Added a benchmark script for timing various ways to access variables:
Tools/scripts/var_access_benchmark.py
.
(Contributed by Raymond Hettinger in bpo-35884.)
Here’s a summary of performance improvements since Python 3.3:
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 running the macOS 64-bit builds found at python.org. The benchmark script displays timings in nanoseconds.
Notable changes in Python 3.8.1¶
Due to significant security concerns, the reuse_address parameter of
asyncio.loop.create_datagram_endpoint()
is no longer supported. This is
because of the behavior of the socket option SO_REUSEADDR
in UDP. For more
details, see the documentation for loop.create_datagram_endpoint()
.
(Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in
bpo-37228.)
Notable changes in Python 3.8.2¶
Fixed a regression with the ignore
callback of shutil.copytree()
.
The argument types are now str and List[str] again.
(Contributed by Manuel Barkhau and Giampaolo Rodola in gh-83571.)
Notable changes in Python 3.8.3¶
The constant values of future flags in the __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)
Notable changes in Python 3.8.8¶
Earlier Python versions allowed using both ;
and &
as
query parameter separators in urllib.parse.parse_qs()
and
urllib.parse.parse_qsl()
. Due to security concerns, and to conform with
newer W3C recommendations, this has been changed to allow only a single
separator key, with &
as the default. This change also affects
cgi.parse()
and cgi.parse_multipart()
as they use the affected
functions internally. For more details, please see their respective
documentation.
(Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in bpo-42967.)
Notable changes in Python 3.8.9¶
A security fix alters the 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)
Notable changes in Python 3.8.10¶
macOS 11.0 (Big Sur) and Apple Silicon Mac support¶
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)
Notable changes in Python 3.8.10¶
urllib.parse¶
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 urllib.parse
preventing such attacks. The removal
characters are controlled by a new module level variable
urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE
. (See bpo-43882)
Notable changes in Python 3.8.12¶
Changes in the Python API¶
Starting with Python 3.8.12 the 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 socket.inet_aton()
treats leading zeros as octal notation.
glibc implementation of modern inet_pton()
does not accept
any leading zeros.
(Originally contributed by Christian Heimes in bpo-36384, and backported to 3.8 by Achraf Merzouki.)
Notable security feature in 3.8.14¶
Converting between int
and str
in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal)
now raises a ValueError
if the number of digits in string form is
above a limit to avoid potential denial of service attacks due to the
algorithmic complexity. This is a mitigation for CVE 2020-10735.
This limit can be configured or disabled by environment variable, command
line flag, or sys
APIs. See the integer string conversion
length limitation documentation. The default limit
is 4300 digits in string form.
Notable changes in 3.8.17¶
tarfile¶
The extraction methods in
tarfile
, andshutil.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 Extraction filters for details. In Python 3.12, use without the filter argument will show aDeprecationWarning
. In Python 3.14, the default will switch to'data'
. (Contributed by Petr Viktorin in PEP 706.)