- 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 largerexpression. It is affectionately known as “the walrus operator” due toits resemblance to the eyes and tusks of a walrus.
In this example, the assignment expression helps avoid callinglen()
twice:
if (n := len(a)) > 10: print(f"List is too long ({n} elements, expected <= 10)")
A similar benefit arises during regular expression matching wherematch objects are needed twice, once to test whether a matchoccurred and another to extract a subgroup:
discount = 0.0if (mo := re.search(r'(\d+)% discount', advertisem*nt)): discount = float(mo.group(1)) / 100.0
The operator is also useful with while-loops that computea value to test loop termination and then need that samevalue again in the body of the loop:
# Loop over fixed length blockswhile (block := f.read(256)) != '': process(block)
Another motivating use case arises in list comprehensions wherea value computed in a filtering condition is also needed inthe 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 reducecomplexity 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 somefunction parameters must be specified positionally and cannot be used askeyword arguments. This is the same notation shown by help()
for Cfunctions 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 arerequired 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 argumentf(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 functionsto 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 parametername is not helpful. For example, the builtin len()
function hasthe 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 itallows the parameter name to be changed in the future without risk ofbreaking client code. For example, in the statistics
module, theparameter name dist may be changed in the future. This was madepossible with the following function specification:
def quantiles(dist, /, *, n=4, method='exclusive') ...
Since the parameters to the left of /
are not exposed as possiblekeywords, 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 ways10 20 {'a': 1, 'b': 2, 'c': 3}
This greatly simplifies the implementation of functions and methodsthat need to accept arbitrary keyword arguments. For example, hereis 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 bytecodecache to use a separate parallel filesystem tree, rather thanthe default __pycache__
subdirectories within each sourcedirectory.
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. OnUnix, when Python is built in debug mode, it is now possible to load Cextensions built in release mode and C extensions built using the stable ABI.
Release builds and debug builds are now ABI compatible: defining thePy_DEBUG
macro no longer implies the Py_TRACE_REFS
macro, whichintroduces the only ABI incompatibility. The Py_TRACE_REFS
macro, whichadds 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 Androidand Cygwin.It is now possiblefor a statically linked Python to load a C extension built using a sharedlibrary Python.(Contributed by Victor Stinner in bpo-21536.)
On Unix, when Python is built in debug mode, import now also looks for Cextensions compiled in release mode and for C extensions compiled with thestable ABI.(Contributed by Victor Stinner in bpo-36722.)
To embed Python into an application, a new --embed
option must be passed topython3-config --libs --embed
to get -lpython3.8
(link the applicationto 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 anapplication: 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
firstand fallback to pkg-config python-X.Y --libs
(without --embed
) if theprevious 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 onAndroid 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 asf'{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 morecontrol 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 thatcalculations 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 fromPython and native code, allowing applications and frameworks written in purePython code to take advantage of extra notifications, while also allowingembedders or system administrators to deploy builds of Python where auditing isalways enabled.
See PEP 578 for full details.
PEP 587: Python Initialization Configuration¶
The PEP 587 adds a new C API to configure the Python Initializationproviding 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 theseinternal structures. PyInterpreterState.config
becomes the newreference configuration, replacing global configuration variables andother private variables.
See Python Initialization Configuration for thedocumentation.
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 donefor various classes.Any static type implementing a callable can use thisprotocol.
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 processesin order to take advantage of multi-core or multi-machine processing,it is important to optimize the transfer by reducing memory copies, andpossibly by applying custom techniques such as data-dependent compression.
The pickle
protocol 5 introduces support for out-of-band bufferswhere PEP 3118-compatible data can be transmitted separately from themain 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
clausedue to a problem with the implementation. In Python 3.8 this restrictionwas lifted.(Contributed by Serhiy Storchaka in bpo-32489.)The
bool
,int
, andfractions.Fraction
typesnow have anas_integer_ratio()
method like that found infloat
anddecimal.Decimal
. This minor API extensionmakes 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 inbpo-37819.)Constructors of
int
,float
andcomplex
will nowuse the__index__()
special method, if available and thecorresponding 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 furtherrestricted. In particular,
f((keyword)=arg)
is no longer allowed. It wasnever intended to permit more than a bare name on the left-hand side of akeyword 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 withnormal 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)]
, thecompiler displays aSyntaxWarning
with a helpful suggestion.This improves on just having aTypeError
indicating that thefirst tuple was not callable. (Contributed by Serhiy Storchaka inbpo-15248.)Arithmetic operations between subclasses of
datetime.date
ordatetime.datetime
anddatetime.timedelta
objects now returnan instance of the subclass, rather than the base class. This also affectsthe 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 theresulting
KeyboardInterrupt
exception is not caught, the Python processnow exits via a SIGINT signal or with the correct exit code such that thecalling process can detect that it died due to a Ctrl-C. Shells on POSIXand 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 codeobjects are immutable, a new code object needs to be created, onethat is modeled on the existing code object. With 19 parameters,this was somewhat tedious. Now, the newreplace()
method makesit possible to create a clone with a few altered parameters.Here’s an example that alters the
statistics.mean()
function toprevent 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 nowpermits the exponent to be negative in the case where the base isrelatively prime to the modulus. It then computes a modular inverse tothe base when the exponent is-1
, and a suitable power of thatinverse for other negative exponents. For example, to compute themodular multiplicative inverse of 38modulo 137, write:>>> pow(38, -1, 137)119>>> 119 * 38 % 1371
Modular inverses arise in the solution of linear Diophantineequations.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 * y369
(Contributed by Mark Dickinson in bpo-36027.)
Dict comprehensions have been synced-up with dict literals so that thekey is computed first and the value second:
>>> # Dict comprehension>>> cast = {input('role? '): input('actor? ') for i in range(2)}role? King Arthuractor? Chapmanrole? Black Knightactor? Cleese>>> # Dict literal>>> cast = {input('role? '): input('actor? ')}role? Sir Robinactor? Eric Idle
The guaranteed execution order is helpful with assignment expressionsbecause variables assigned in the key expression will be available inthe 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 tosix elements long. Formerly, five was the limit. The new, optional sixthelement is a callable with a(obj, state)
signature. This allows thedirect control over the state-updating behavior of a specific object. Ifnot 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 forreading metadata from third-party packages. For example, it can extract aninstalled 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 onlyapplies to nodes that have lineno
and col_offset
attributes.)
New function ast.get_source_segment()
returns the source codefor 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 andPEP 526 type comments associated with certain AST nodes;mode='func_type'
can be used to parse PEP 484 “signature typecomments” (returned for function definition AST nodes);feature_version=(3, N)
allows specifying an earlier Python 3version. 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. Thisfunction can be used to execute a coroutine and return the result whileautomatically managing the event loop. For example:
import asyncioasync def main(): await asyncio.sleep(0) return 42asyncio.run(main())
This is roughly equivalent to:
import asyncioasync def main(): await asyncio.sleep(0) return 42loop = 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 rapidexperimentation with code that has a top-level await
. There is nolonger a need to directly call asyncio.run()
which would spawn a new eventloop on every invocation:
$ python -m asyncioasyncio REPL 3.8.0Use "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 fromBaseException
rather than Exception
and no longer inheritsfrom 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 byKeyboardInterrupt
(“CTRL+C”).(Contributed by Vladimir Matveev in bpo-23057.)
Added asyncio.Task.get_coro()
for getting the wrapped coroutinewithin an asyncio.Task
.(Contributed by Alex Grönholm in bpo-36999.)
Asyncio tasks can now be named, either by passing the name
keywordargument to asyncio.create_task()
orthe create_task()
event loop method, or bycalling the set_name()
method on the task object. Thetask name is visible in the repr()
output of asyncio.Task
andcan also be retrieved using the get_name()
method.(Contributed by Alex Grönholm in bpo-34270.)
Added support forHappy Eyeballs toasyncio.loop.create_connection()
. To specify the behavior, two newparameters have been added: happy_eyeballs_delay and interleave. The HappyEyeballs algorithm improves responsiveness in applications that support IPv4and 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 theast.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 objectmarked with the CO_COROUTINE
flag may then be returned.(Contributed by Matthias Bussonnier in bpo-34616)
collections¶
The _asdict()
method forcollections.namedtuple()
now returns a dict
instead of acollections.OrderedDict
. This works because regular dicts haveguaranteed ordering since Python 3.7. If the extra features ofOrderedDict
are required, the suggested remediation is to cast theresult 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 cProfilewith 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 ofa collections.OrderedDict
. The tool is now faster and uses lessmemory while still preserving the field order.(Contributed by Michael Selik in bpo-34003.)
curses¶
Added a new variable holding structured version information for theunderlying ncurses library: ncurses_version
.(Contributed by Serhiy Storchaka in bpo-31680.)
ctypes¶
On Windows, CDLL
and subclasses now accept a winmode parameterto specify flags for the underlying LoadLibraryEx
call. The default flags areset to only load DLL dependencies from trusted locations, including the pathwhere the DLL is stored (if a full or partial path is used to load the initialDLL) and paths added by add_dll_directory()
.(Contributed by Steve Dower in bpo-36085.)
datetime¶
Added new alternate constructors datetime.date.fromisocalendar()
anddatetime.datetime.fromisocalendar()
, which construct date
anddatetime
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 ratherthan as a function returning a decorator. So both of these are now supported:
@lru_cachedef 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 propertiescached for the life of the instance.
import functoolsimport statisticsclass 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 convertsmethods into generic functions usingsingle dispatch:
from functools import singledispatchmethodfrom contextlib import suppressclass 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 parameterindicating 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 inbpo-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 theSettings dialog. Fewer, but possibly extra long, lines can be squeezed byright clicking on the output. Squeezed output can be expanded in placeby double-clicking the button or into the clipboard or a separate windowby right-clicking the button. (Contributed by Tal Einat in bpo-1529353.)
Add “Run Customized” to the Run menu to run a module with customizedsettings. Any command line arguments entered are added to sys.argv.They also re-appear in the box for the next customized run. One can alsosuppress the normal Shell main module restart. (Contributed by CherylSabella, Terry Jan Reedy, and others in bpo-5680 and bpo-37627.)
Added optional line numbers for IDLE editor windows. Windowsopen without line numbers unless set otherwise in the Generaltab of the configuration dialog. Line numbers for an existingwindow 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 Tclobjects. This allows IDLE to work with emoji and other non-BMP characters.These characters can be displayed or copied and pasted to or from theclipboard. Converting strings from Tcl to Python and back now never fails.(Many people worked on this for eight years but the problem was finallysolved by Serhiy Storchaka in bpo-13153.)
New in 3.8.1:
Add option to toggle cursor blink off. (Contributed by Zackery Spytzin bpo-4603.)
Escape key now closes IDLE completion windows. (Contributed by JohnnyNajera 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 havefor 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, theio.IOBase
finalizer now logs the exception if the close()
methodfails. 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 keywordargument 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 attachedto the root logger are removed and closed before carrying out theconfiguration specified by the other arguments.
This solves a long-standing problem. Once a logger or basicConfig() hadbeen called, subsequent calls to basicConfig() were silently ignored.This made it difficult to update, experiment with, or teach the variouslogging configuration options using the interactive prompt or a Jupyternotebook.
(Suggested by Raymond Hettinger, implemented by Donghee Na, andreviewed by Vinay Sajip in bpo-33897.)
math¶
Added new function math.dist()
for computing Euclidean distancebetween 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 ofnumbers:
>>> 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 time720>>> math.comb(10, 3) # Combinations of 10 things taken 3 at a time120
(Contributed by Yash Aggarwal, Keller Fuchs, Serhiy Storchaka, and RaymondHettinger in bpo-37128, bpo-37178, and bpo-35431.)
Added a new function math.isqrt()
for computing accurate integer squareroots without conversion to floating point. The new function supportsarbitrarily large integers. It is faster than floor(sqrt(n))
but slowerthan math.sqrt()
:
>>> r = 650320427>>> s = r ** 2>>> isqrt(s - 1) # correct650320426>>> floor(sqrt(s - 1)) # incorrect650320427
(Contributed by Mark Dickinson in bpo-36887.)
The function math.factorial()
no longer accepts arguments that are notint-like. (Contributed by Pablo Galindo in bpo-33083.)
mmap¶
The mmap.mmap
class now has an madvise()
method toaccess 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 providingadditional search paths for native dependencies when importing extensionmodules or loading DLLs using ctypes
.(Contributed by Steve Dower in bpo-36085.)
A new os.memfd_create()
function was added to wrap thememfd_create()
syscall.(Contributed by Zackery Spytz and Christian Heimes in bpo-26836.)
On Windows, much of the manual logic for handling reparse points (includingsymlinks and directory junctions) has been delegated to the operating system.Specifically, os.stat()
will now traverse anything supported by theoperating system, while os.lstat()
will only open reparse points thatidentify as “name surrogates” while others are opened as for os.stat()
.In all cases, stat_result.st_mode
will only have S_IFLNK
set forsymbolic links and not other kinds of reparse points. To identify other kindsof reparse point, check the new stat_result.st_reparse_tag
attribute.
On Windows, os.readlink()
is now able to read directory junctions. Notethat islink()
will return False
for directory junctions,and so code that checks islink
first will continue to treat junctions asdirectories, while code that handles errors from os.readlink()
may nowtreat junctions as links.
(Contributed by Steve Dower in bpo-37834.)
os.path¶
os.path
functions that return a boolean result likeexists()
, lexists()
, isdir()
,isfile()
, islink()
, and ismount()
now return False
instead of raising ValueError
or its subclassesUnicodeEncodeError
and UnicodeDecodeError
for paths that containcharacters 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 setfor regular user accounts.(Contributed by Anthony Sottile in bpo-36264.)
isdir()
on Windows no longer returns True
for a link to anon-existent directory.
realpath()
on Windows now resolves reparse points, includingsymlinks and directory junctions.
(Contributed by Steve Dower in bpo-37834.)
pathlib¶
pathlib.Path
methods that return a boolean result likeexists()
, is_dir()
,is_file()
, is_mount()
,is_symlink()
, is_block_device()
,is_char_device()
, is_fifo()
,is_socket()
now return False
instead of raisingValueError
or its subclass UnicodeEncodeError
for paths thatcontain characters unrepresentable at the OS level.(Contributed by Serhiy Storchaka in bpo-33721.)
Added pathlib.Path.link_to()
which creates a hard link pointingto a path.(Contributed by Joannah Nanjekye in bpo-26978)Note that link_to
was deprecated in 3.10 and removed in 3.12 infavor of a hardlink_to
method added in 3.10 which matches thesemantics 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 thespecial reducer_override()
method.(Contributed by Pierre Glaser and Olivier Grisel in bpo-35900.)
plistlib¶
Added new plistlib.UID
and enabled support for reading and writingNSKeyedArchiver-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 orprinting. However, if sort_dicts is set to false, the dictionaries retainthe order that keys were inserted. This can be useful for comparison to JSONinputs during debugging.
In addition, there is a convenience new function, pprint.pp()
that islike 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 withoutrecursively 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 whencreating a server socket, including accepting both IPv4 and IPv6 connectionson the same socket. (Contributed by Giampaolo Rodolà in bpo-17561.)
The socket.if_nameindex()
, socket.if_nametoindex()
, andsocket.if_indextoname()
functions have been implemented on Windows.(Contributed by Zackery Spytz in bpo-37007.)
ssl¶
Added post_handshake_auth
to enable andverify_client_post_handshake()
to initiate TLS 1.3post-handshake authentication.(Contributed by Christian Heimes in bpo-34670.)
statistics¶
Added statistics.fmean()
as a faster, floating-point variant ofstatistics.mean()
. (Contributed by Raymond Hettinger andSteven 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 mostcommon values. (Contributed by Raymond Hettinger in bpo-35892.)
Added statistics.quantiles()
that divides data or a distributionin to equiprobable intervals (e.g. quartiles, deciles, or percentiles).(Contributed by Raymond Hettinger in bpo-36546.)
Added statistics.NormalDist
, a tool for creatingand 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.mean6.0>>> temperature_feb.stdev6.356099432828281>>> temperature_feb.cdf(3) # Chance of being under 3 degrees0.3184678262814532>>> # 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_febNormalDist(mu=10.0, sigma=6.830080526611674)>>> temperature_feb * (9/5) + 32 # Convert to FahrenheitNormalDist(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 controlhow “unraisable exceptions” are handled. It is called when an exception hasoccurred but there is no way for Python to handle it. For example, when adestructor 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 uncaughtthreading.Thread.run()
exception. It can be overridden to control howuncaught threading.Thread.run()
exceptions are handled.(Contributed by Victor Stinner in bpo-1230540.)
Add a new threading.get_native_id()
function anda native_id
attribute to the threading.Thread
class. These return the nativeintegral Thread ID of the current thread assigned by the kernel.This feature is only available on certain platforms, seeget_native_id
for more information.(Contributed by Jake Tesler in bpo-36084.)
tokenize¶
The tokenize
module now implicitly emits a NEWLINE
token whenprovided with input that does not have a trailing new line. This behaviornow matches what the C tokenizer does internally.(Contributed by Ammar Askar in bpo-33899.)
tkinter¶
Added methods selection_from()
,selection_present()
,selection_range()
andselection_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 hastransparency_get()
andtransparency_set()
methods. (Contributed byZackery 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 requiredto 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 valueis 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 restrictsubclassing, 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 stringis in a specific normal form, often much faster than by actually normalizingthe string. (Contributed by Max Belanger, David Euresti, and Greg Price inbpo-32285 and bpo-37966).
unittest¶
Added AsyncMock
to support an asynchronous version ofMock
. Appropriate new assert functions for testinghave been added as well.(Contributed by Lisa Roach in bpo-26467).
Added addModuleCleanup()
andaddClassCleanup()
to unittest to supportcleanups for setUpModule()
andsetUpClass()
.(Contributed by Lisa Roach in bpo-24412.)
Several mock assert functions now also print a list of actual calls uponfailure. (Contributed by Petter Strandmark in bpo-35047.)
unittest
module gained support for coroutines to be used as test caseswith unittest.IsolatedAsyncioTestCase
.(Contributed by Andrew Svetlov in bpo-32972.)
Example:
import unittestclass 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 foractivating 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 matrixmultiplication operators @
and @=
in addition to the othernumeric operators. (Contributed by Mark Dickinson in bpo-36669.)
xml¶
As mitigation against DTD and external entity retrieval, thexml.dom.minidom
and xml.sax
modules no longer processexternal entities by default.(Contributed by Christian Heimes in bpo-17239.)
The .find*()
methods in the xml.etree.ElementTree
modulesupport wildcard searches like {*}tag
which ignores the namespaceand {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–xml.etree.ElementTree.canonicalize()
that implements C14N 2.0.(Contributed by Stefan Behnel in bpo-13611.)
The target object of xml.etree.ElementTree.XMLParser
canreceive namespace declaration events through the new callback methodsstart_ns()
and end_ns()
. Additionally, thexml.etree.ElementTree.TreeBuilder
target can be configuredto process events about comments and processing instructions to includethem in the generated tree.(Contributed by Stefan Behnel in bpo-36676 and bpo-36673.)
xmlrpc¶
xmlrpc.client.ServerProxy
now supports an optional headers keywordargument for a sequence of HTTP headers to be sent with each request. Amongother things, this makes it possible to upgrade from default basicauthentication to faster session authentication.(Contributed by Cédric Krier in bpo-35153.)
Optimizations¶
The
subprocess
module can now use theos.posix_spawn()
functionin some cases for better performance. Currently, it is only used on macOSand 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 parametersare 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 filemore 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 MiBinstead 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 cyclesare consumed.See Platform-dependent efficient copy operations section.(Contributed by Giampaolo Rodolà in bpo-33671.)shutil.copytree()
usesos.scandir()
function and all copyfunctions depending from it use cachedos.stat()
values. The speedupfor copying a directory with 8000 files is around +9% on Linux, +20% onWindows and +30% on a Windows SMB share. Also the number ofos.stat()
syscalls is reduced by 38% makingshutil.copytree()
especially fasteron 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 smallersize compared to Protocol 3 available since Python 3.0.Removed one
Py_ssize_t
member fromPyGC_Head
. All GC trackedobjects (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%. Optimizedargument handling and added a fast path for the common case of a singlenon-negative integer index into a tuple (which is the typical use case inthe standard library). (Contributed by Raymond Hettinger inbpo-35664.)Sped-up field lookups in
collections.namedtuple()
. They are now morethan two times faster, making them the fastest form of instance variablelookup in Python. (Contributed by Raymond Hettinger, Pablo Galindo, andJoe Jevnik, Serhiy Storchaka in bpo-32492.)The
list
constructor does not overallocate the internal item bufferif the input iterable has a known length (the input implements__len__
).This makes the created list 12% smaller on average. (Contributed byRaymond Hettinger and Pablo Galindo in bpo-33234.)Doubled the speed of class variable writes. When a non-dunder attributewas 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 functionsand methods. This sped up calling some simple builtin functions andmethods 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 inbpo-26219.)
Build and C API Changes¶
Default
sys.abiflags
became an empty string: them
flag forpymalloc 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
scriptis gone.The
m
flag has been removed from the suffix of dynamic libraryfilenames: extension modules in the standard library as well as thoseproduced and installed by third-party packages, like those downloaded fromPyPI. 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 kindsof 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 toCPython. This API comes with no backward compatibility warranty and shouldnot be used outside CPython. It is only exposed for very specific needslike debuggers and profiles which has to access to CPython internalswithout 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 typesand 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 havebeen removed. They did nothing since Python 2.7.4 and Python 3.2.0, wereexcluded 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 beenremoved. Previously, when updating the CPython source tree, one hadto manually copyModules/Setup.dist
(inside the source tree) toModules/Setup
(inside the build tree) in order to reflect any changesupstream. This was of a small benefit to packagers at the expense ofa frequent annoyance to developers following CPython development, asforgetting to copy the file could produce build failures.Now the build system always reads from
Modules/Setup
inside the sourcetree. People who want to customize that file are encouraged to maintaintheir changes in a git fork of CPython or as patch files, as they would dofor 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 beemitted 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 ifavailable.(Contributed by Serhiy Storchaka in bpo-36048 and bpo-20092.)Heap-allocated type objects will now increase their reference countin
PyObject_Init()
(and its parallel macroPyObject_INIT
)instead of inPyType_GenericAlloc()
. Types that modify instanceallocation or deallocation may need to be adjusted.(Contributed by Eddie Elizondo in bpo-35810.)The new function
PyCode_NewWithPosOnlyArgs()
allows to createcode objects likePyCode_New()
, but with an extra posonlyargcountparameter for indicating the number of positional-only arguments.(Contributed by Pablo Galindo in bpo-37221.)Py_SetPath()
now setssys.executable
to the program fullpath (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()
intheElementTree
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()
isdeprecated 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 beendeprecated.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 sameinformation. (Contributed by Raymond Hettinger in bpo-36320.)ast
classesNum
,Str
,Bytes
,NameConstant
andEllipsis
are considered deprecated and will be removed in future Pythonversions.Constant
should be used instead.(Contributed by Serhiy Storchaka in bpo-32892.)ast.NodeVisitor
methodsvisit_Num()
,visit_Str()
,visit_Bytes()
,visit_NameConstant()
andvisit_Ellipsis()
aredeprecated now and will not be called in future Python versions.Add thevisit_Constant()
method to handle allconstant nodes.(Contributed by Serhiy Storchaka in bpo-36917.)The
asyncio.coroutine()
decorator is deprecated and will beremoved 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 beendeprecated 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 beendeprecated 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 unexpectedUnicode-related exceptions if there are encoding problems with thetranslated strings. It’s much better to use alternatives which returnUnicode strings in Python 3. These functions have been broken for a long time.Function
bind_textdomain_codeset()
, methodsoutput_charset()
andset_output_charset()
, and the codesetparameter of functionstranslation()
andinstall()
are also deprecated, since they are only used forthel*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 willnow emit a deprecation warning for
Decimal
s,Fraction
s and any other objects that can be convertedto integers only with a loss (e.g. that have the__int__()
method but do not have the__index__()
method). In futureversion 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
wasdeprecated, and importing should be done fromcollections.abc
. Beingable to import from collections was marked for removal in 3.8, but has beendelayed to 3.9. (See bpo-36952.)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 beendeprecated since Python 3.3: useos.popen()
instead.(Contributed by Victor Stinner in bpo-35345.)The function
time.clock()
has been removed, after having beendeprecated since Python 3.3: usetime.perf_counter()
ortime.process_time()
instead, dependingon 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 importedfrom 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 acceptsthe 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 notexposed 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 3.6has 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 bugfixesthat may require changes to your code.
Changes in Python behavior¶
Yield expressions (both
yield
andyield from
clauses) are now disallowedin comprehensions and generator expressions (aside from the iterable expressionin 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 usersto use equality tests (==
and!=
) instead.(Contributed by Serhiy Storchaka in bpo-34850.)The CPython interpreter can swallow exceptions in some circ*mstances.In Python 3.8 this happens in fewer cases. In particular, exceptionsraised when getting the attribute from the type dictionary are no longerignored. (Contributed by Serhiy Storchaka in bpo-35459.)
Removed
__str__
implementations from builtin typesbool
,int
,float
,complex
and few classes fromthe standard library. They now inherit__str__()
fromobject
.As result, defining the__repr__()
method in the subclass of theseclasses 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'
. Sinceolder Python versions include the version number, so it is recommended toalways usesys.platform.startswith('aix')
.(Contributed by M. Felt in bpo-36588.)PyEval_AcquireLock()
andPyEval_AcquireThread()
nowterminate the current thread if called while the interpreter isfinalizing, making them consistent withPyEval_RestoreThread()
,Py_END_ALLOW_THREADS()
, andPyGILState_Ensure()
. If thisbehavior 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. Thefunction is no longer deprecated on Windows.(Contributed by Victor Stinner in bpo-37412.)subprocess.Popen
can now useos.posix_spawn()
in some casesfor better performance. On Windows Subsystem for Linux and QEMU UserEmulation, thePopen
constructor usingos.posix_spawn()
no longer raises anexception on errors like “missing program”. Instead the child process fails with anon-zeroreturncode
.(Contributed by Joannah Nanjekye and Victor Stinner in bpo-35537.)The preexec_fn argument of *
subprocess.Popen
is no longercompatible with subinterpreters. The use of the parameter in asubinterpreter now raisesRuntimeError
.(Contributed by Eric Snow in bpo-34651, modified by Christian Heimesin bpo-37951.)The
imap.IMAP4.logout()
method no longer silently ignores arbitraryexceptions.(Contributed by Victor Stinner in bpo-36348.)The function
platform.popen()
has been removed, after having been deprecated sincePython 3.3: useos.popen()
instead.(Contributed by Victor Stinner in bpo-35345.)The
statistics.mode()
function no longer raises an exceptionwhen given multimodal data. Instead, it returns the first modeencountered in the input data. (Contributed by Raymond Hettingerin bpo-35892.)The
selection()
method of thetkinter.ttk.Treeview
class no longer takes arguments. Using it witharguments for changing the selection was deprecated in Python 3.6. Usespecialized methods likeselection_set()
forchanging the selection. (Contributed by Serhiy Storchaka in bpo-31508.)The
writexml()
,toxml()
andtoprettyxml()
methods ofxml.dom.minidom
, and thewrite()
method ofxml.etree
,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 createsa 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 willemit 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’tprovide the__classcell__
entry in the namespace passed totype.__new__
. ADeprecationWarning
was emitted in Python3.6–3.7. (Contributed by Serhiy Storchaka in bpo-23722.)The
cProfile.Profile
class can now be used as a contextmanager. (Contributed by Scott Sanderson in bpo-29235.)shutil.copyfile()
,shutil.copy()
,shutil.copy2()
,shutil.copytree()
andshutil.move()
use platform-specific“fast-copy” syscalls (seePlatform-dependent efficient copy operations section).shutil.copyfile()
default buffer size on Windows was changed from16 KiB to 1 MiB.The
PyGC_Head
struct has changed completely. All code that touched thestruct member should be rewritten. (See bpo-33597.)The
PyInterpreterState
struct has been moved into the “internal”header files (specifically Include/internal/pycore_pystate.h). AnopaquePyInterpreterState
is still available as part of the publicAPI (and stable ABI). The docs indicate that none of the struct’sfields 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 noalternative then please open a BPO issue. We’ll work on helpingyou adjust (possibly including adding accessor functions to thepublic API). (See bpo-35886.)The
mmap.flush()
method now returnsNone
onsuccess 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 onsuccess; an exception was raised on error under Unix.(Contributed by Berker Peksag in bpo-2122.)xml.dom.minidom
andxml.sax
modules no longer processexternal 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 returnan instance ofConstant
.(Contributed by Serhiy Storchaka in bpo-32892.)expanduser()
on Windows now prefers theUSERPROFILE
environment variable and does not useHOME
, which is not normallyset for regular user accounts.(Contributed by Anthony Sottile in bpo-36264.)The exception
asyncio.CancelledError
now inherits fromBaseException
rather thanException
and no longer inheritsfromconcurrent.futures.CancelledError
.(Contributed by Yury Selivanov in bpo-32528.)The function
asyncio.wait_for()
now correctly waits for cancellationwhen using an instance ofasyncio.Task
. Previously, upon reachingtimeout, it was cancelled and immediately returned.(Contributed by Elvis Pranskevichus in bpo-32751.)The function
asyncio.BaseTransport.get_extra_info()
now returns a safeto 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
onWindows are now resolved more securely. Only the system paths, the directorycontaining 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 longerused, and modifications to these will no longer have any effect on normal DLLresolution. If your application relies on these mechanisms, you should checkforadd_dll_directory()
and if it exists, use it to add your DLLsdirectory while loading your library. Note that Windows 7 users will need toensure that Windows Update KB2533623 has been installed (this is also verifiedby the installer).(Contributed by Steve Dower in bpo-36085.)The header files and functions related to pgen have been removed after itsreplacement by a pure Python implementation. (Contributed by Pablo Galindoin bpo-36623.)
types.CodeType
has a new parameter in the second position of theconstructor (posonlyargcount) to support positional-only arguments definedin PEP 570. The first argument (argcount) now represents the totalnumber of positional arguments (including positional-only arguments). The newreplace()
method oftypes.CodeType
can be used to make the codefuture-proof.The parameter
digestmod
forhmac.new()
no longer uses the MD5 digestby default.
Changes in the C API¶
The
PyCompilerFlags
structure got a new cf_feature_versionfield. It should be initialized toPY_MINOR_VERSION
. The field is ignoredby default, and is used if and only ifPyCF_ONLY_AST
flag is set incf_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 Androidand 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 whichwere not linked tolibpython
, like C extensions of the standardlibrary 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 likeother 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 allocatingan instance (perhaps to work around the bug) may now become immortal.To avoid this, these classes need to call Py_DECREF on the type objectduring instance deallocation.
To correctly port these types into 3.8, please apply the followingchanges:
Remove
Py_INCREF
on the type object after allocating aninstance - 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 typesdecrease the type’s reference count.Example:
static voidfoo_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 ofextension types across feature releases, anymore. A
PyTypeObject
exported by a third-party extension module is supposed to have all theslots 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 accepttwo 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.defdlltool --dllname python38.dll --def tmp.def --output-lib libpython38.a
The location of an installed
pythonXY.dll
will depend on theinstallation options and the version and language of Windows. SeeUsing Python on Windows for more information. The resulting library should beplaced 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 unrollingthe stack of blocks into the compiler. The compiler emits now explicitinstructions for adjusting the stack of values and calling thecleaning-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 inbpo-17611.)
Added new opcode
END_ASYNC_FOR
for handling exceptions raisedwhen 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 thestack and the key as the second element. This change was made so the keyis always evaluated before the value in dictionary comprehensions, asproposed 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 27.7Variable 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 25.7Data 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 18.9Data 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 23.1Stack (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 42.8Timing loop: loop_overhead 0.3 0.5 0.6 0.4 0.3 0.3
The benchmarks were measured on anIntel® Core™ i7-4960HQ processorrunning the macOS 64-bit builds found atpython.org.The benchmark script displays timings in nanoseconds.
Notable changes in Python 3.8.1¶
Due to significant security concerns, the reuse_address parameter ofasyncio.loop.create_datagram_endpoint()
is no longer supported. This isbecause of the behavior of the socket option SO_REUSEADDR
in UDP. For moredetails, see the documentation for loop.create_datagram_endpoint()
.(Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov inbpo-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__
moduleare updated in order to prevent collision with compiler flags. PreviouslyPyCF_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 &
asquery parameter separators in urllib.parse.parse_qs()
andurllib.parse.parse_qsl()
. Due to security concerns, and to conform withnewer W3C recommendations, this has been changed to allow only a singleseparator key, with &
as the default. This change also affectscgi.parse()
and cgi.parse_multipart()
as they use the affectedfunctions internally. For more details, please see their respectivedocumentation.(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 theIPv4 address sent from the remote server when setting up a passive datachannel. We reuse the ftp server IP address instead. For unusual coderequiring 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 nativelysupport both ARM64
and Intel 64
in one set of executables.Note that support for “weaklinking”, building binaries targeted for newerversions of macOS that will also run correctly on older versions bytesting at runtime for missing features, is not included in this backportfrom Python 3.9; to support a range of macOS versions, continue to targetfor 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 Bélangerand 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 someforms of attacks. Following the WHATWG specification that updates RFC 3986,ASCII newline \n
, \r
and tab \t
characters are stripped from theURL by the parser in urllib.parse
preventing such attacks. The removalcharacters are controlled by a new module level variableurllib.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 acceptsany leading zeros in IPv4 address strings. Leading zeros are ambiguous andinterpreted as octal notation by some libraries. For example the legacyfunction socket.inet_aton()
treats leading zeros as octal notation.glibc implementation of modern inet_pton()
does not acceptany leading zeros.
(Originally contributed by Christian Heimes in bpo-36384, and backportedto 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 isabove a limit to avoid potential denial of service attacks due to thealgorithmic complexity. This is a mitigation for CVE-2020-10735.This limit can be configured or disabled by environment variable, commandline flag, or sys
APIs. See the integer string conversionlength limitation documentation. The default limitis 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 besurprising or dangerous, such as creating files outside the destinationdirectory.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.)