What’s New In Python 3.9

What’s New In Python 3.9¶
- Editor:
Łukasz Langa
This article explains the new features in Python 3.9, compared to 3.8. Python 3.9 was released on October 5, 2020. For full details, see the changelog.
See also
PEP 596 - Python 3.9 Release Schedule
Summary – Release highlights¶
New syntax features:
PEP 584, union operators added to
dict
;PEP 585, type hinting generics in standard collections;
PEP 614, relaxed grammar restrictions on decorators.
New built-in features:
PEP 616, string methods to remove prefixes and suffixes.
New features in the standard library:
PEP 593, flexible function and variable annotations;
os.pidfd_open()
added that allows process management without races and signals.
Interpreter improvements:
PEP 573, fast access to module state from methods of C extension types;
PEP 617, CPython now uses a new parser based on PEG;
a number of Python builtins (range, tuple, set, frozenset, list, dict) are now sped up using PEP 590 vectorcall;
garbage collection does not block on resurrected objects;
a number of Python modules (
_abc
,audioop
,_bz2
,_codecs
,_contextvars
,_crypt
,_functools
,_json
,_locale
,math
,operator
,resource
,time
,_weakref
) now use multiphase initialization as defined by PEP 489;a number of standard library modules (
audioop
,ast
,grp
,_hashlib
,pwd
,_posixsubprocess
,random
,select
,struct
,termios
,zlib
) are now using the stable ABI defined by PEP 384.
New library modules:
PEP 615, the IANA Time Zone Database is now present in the standard library in the
zoneinfo
module;an implementation of a topological sort of a graph is now provided in the new
graphlib
module.
Release process changes:
PEP 602, CPython adopts an annual release cycle.
You should check for DeprecationWarning in your code¶
When Python 2.7 was still supported, a lot of functionality in Python 3
was kept for backward compatibility with Python 2.7. With the end of Python
2 support, these backward compatibility layers have been removed, or will
be removed soon. Most of them emitted a DeprecationWarning
warning for
several years. For example, using collections.Mapping
instead of
collections.abc.Mapping
emits a DeprecationWarning
since Python
3.3, released in 2012.
Test your application with the -W
default
command-line option to see
DeprecationWarning
and PendingDeprecationWarning
, or even with
-W
error
to treat them as errors. Warnings Filter can be used to ignore warnings from third-party code.
Python 3.9 is the last version providing those Python 2 backward compatibility layers, to give more time to Python projects maintainers to organize the removal of the Python 2 support and add support for Python 3.9.
Aliases to Abstract Base Classes in
the collections
module, like collections.Mapping
alias to
collections.abc.Mapping
, are kept for one last release for backward
compatibility. They will be removed from Python 3.10.
More generally, try to run your tests in the Python Development Mode which helps to prepare your code to make it compatible with the next Python version.
Note: a number of pre-existing deprecations were removed in this version of Python as well. Consult the Removed section.
New Features¶
Dictionary Merge & Update Operators¶
Merge (|
) and update (|=
) operators have been added to the built-in
dict
class. Those complement the existing dict.update
and
{**d1, **d2}
methods of merging dictionaries.
Example:
>>> x = {"key1": "value1 from x", "key2": "value2 from x"}
>>> y = {"key2": "value2 from y", "key3": "value3 from y"}
>>> x | y
{'key1': 'value1 from x', 'key2': 'value2 from y', 'key3': 'value3 from y'}
>>> y | x
{'key2': 'value2 from x', 'key3': 'value3 from y', 'key1': 'value1 from x'}
See PEP 584 for a full description. (Contributed by Brandt Bucher in bpo-36144.)
New String Methods to Remove Prefixes and Suffixes¶
str.removeprefix(prefix)
and
str.removesuffix(suffix)
have been added
to easily remove an unneeded prefix or a suffix from a string. Corresponding
bytes
, bytearray
, and collections.UserString
methods have also been
added. See PEP 616 for a full description. (Contributed by Dennis Sweeney in
bpo-39939.)
Type Hinting Generics in Standard Collections¶
In type annotations you can now use built-in collection types such as
list
and dict
as generic types instead of importing the
corresponding capitalized types (e.g. List
or Dict
) from
typing
. Some other types in the standard library are also now generic,
for example queue.Queue
.
Example:
def greet_all(names: list[str]) -> None:
for name in names:
print("Hello", name)
See PEP 585 for more details. (Contributed by Guido van Rossum, Ethan Smith, and Batuhan Taşkaya in bpo-39481.)
New Parser¶
Python 3.9 uses a new parser, based on PEG instead of LL(1). The new parser’s performance is roughly comparable to that of the old parser, but the PEG formalism is more flexible than LL(1) when it comes to designing new language features. We’ll start using this flexibility in Python 3.10 and later.
The ast
module uses the new parser and produces the same AST as
the old parser.
In Python 3.10, the old parser will be deleted and so will all
functionality that depends on it (primarily the parser
module,
which has long been deprecated). In Python 3.9 only, you can switch
back to the LL(1) parser using a command line switch (-X
oldparser
) or an environment variable (PYTHONOLDPARSER=1
).
See PEP 617 for more details. (Contributed by Guido van Rossum, Pablo Galindo and Lysandros Nikolaou in bpo-40334.)
Other Language Changes¶
__import__()
now raisesImportError
instead ofValueError
, which used to occur when a relative import went past its top-level package. (Contributed by Ngalim Siregar in bpo-37444.)Python now gets the absolute path of the script filename specified on the command line (ex:
python3 script.py
): the__file__
attribute of the__main__
module became an absolute path, rather than a relative path. These paths now remain valid after the current directory is changed byos.chdir()
. As a side effect, the traceback also displays the absolute path for__main__
module frames in this case. (Contributed by Victor Stinner in bpo-20443.)In the Python Development Mode and in debug build, the encoding and errors arguments are now checked for string encoding and decoding operations. Examples:
open()
,str.encode()
andbytes.decode()
.By default, for best performance, the errors argument is only checked at the first encoding/decoding error and the encoding argument is sometimes ignored for empty strings. (Contributed by Victor Stinner in bpo-37388.)
"".replace("", s, n)
now returnss
instead of an empty string for all non-zeron
. It is now consistent with"".replace("", s)
. There are similar changes forbytes
andbytearray
objects. (Contributed by Serhiy Storchaka in bpo-28029.)Any valid expression can now be used as a decorator. Previously, the grammar was much more restrictive. See PEP 614 for details. (Contributed by Brandt Bucher in bpo-39702.)
Improved help for the
typing
module. Docstrings are now shown for all special forms and special generic aliases (likeUnion
andList
). Usinghelp()
with generic alias likeList[int]
will show the help for the correspondent concrete type (list
in this case). (Contributed by Serhiy Storchaka in bpo-40257.)Parallel running of
aclose()
/asend()
/athrow()
is now prohibited, andag_running
now reflects the actual running status of the async generator. (Contributed by Yury Selivanov in bpo-30773.)Unexpected errors in calling the
__iter__
method are no longer masked byTypeError
in thein
operator and functionscontains()
,indexOf()
andcountOf()
of theoperator
module. (Contributed by Serhiy Storchaka in bpo-40824.)Unparenthesized lambda expressions can no longer be the expression part in an
if
clause in comprehensions and generator expressions. See bpo-41848 and bpo-43755 for details.
New Modules¶
zoneinfo¶
The zoneinfo
module brings support for the IANA time zone database to
the standard library. It adds zoneinfo.ZoneInfo
, a concrete
datetime.tzinfo
implementation backed by the system’s time zone data.
Example:
>>> from zoneinfo import ZoneInfo
>>> from datetime import datetime, timedelta
>>> # Daylight saving time
>>> dt = datetime(2020, 10, 31, 12, tzinfo=ZoneInfo("America/Los_Angeles"))
>>> print(dt)
2020-10-31 12:00:00-07:00
>>> dt.tzname()
'PDT'
>>> # Standard time
>>> dt += timedelta(days=7)
>>> print(dt)
2020-11-07 12:00:00-08:00
>>> print(dt.tzname())
PST
As a fall-back source of data for platforms that don’t ship the IANA database, the tzdata module was released as a first-party package – distributed via PyPI and maintained by the CPython core team.
See also
- PEP 615 – Support for the IANA Time Zone Database in the Standard Library
PEP written and implemented by Paul Ganssle
graphlib¶
A new module, graphlib
, was added that contains the
graphlib.TopologicalSorter
class to offer functionality to perform
topological sorting of graphs. (Contributed by Pablo Galindo, Tim Peters and
Larry Hastings in bpo-17005.)
Improved Modules¶
ast¶
Added the indent option to dump()
which allows it to produce a
multiline indented output.
(Contributed by Serhiy Storchaka in bpo-37995.)
Added ast.unparse()
as a function in the ast
module that can
be used to unparse an ast.AST
object and produce a string with code
that would produce an equivalent ast.AST
object when parsed.
(Contributed by Pablo Galindo and Batuhan Taskaya in bpo-38870.)
Added docstrings to AST nodes that contains the ASDL signature used to construct that node. (Contributed by Batuhan Taskaya in bpo-39638.)
asyncio¶
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.)
Added a new coroutine shutdown_default_executor()
that schedules a shutdown for the default executor that waits on the
ThreadPoolExecutor
to finish closing. Also,
asyncio.run()
has been updated to use the new coroutine.
(Contributed by Kyle Stanley in bpo-34037.)
Added asyncio.PidfdChildWatcher
, a Linux-specific child watcher
implementation that polls process file descriptors. (bpo-38692)
Added a new coroutine asyncio.to_thread()
. It is mainly used for
running IO-bound functions in a separate thread to avoid blocking the event
loop, and essentially works as a high-level version of
run_in_executor()
that can directly take keyword arguments.
(Contributed by Kyle Stanley and Yury Selivanov in bpo-32309.)
When cancelling the task due to a timeout, asyncio.wait_for()
will now
wait until the cancellation is complete also in the case when timeout is
<= 0, like it does with positive timeouts.
(Contributed by Elvis Pranskevichus in bpo-32751.)
asyncio
now raises TypeError
when calling incompatible
methods with an ssl.SSLSocket
socket.
(Contributed by Ido Michael in bpo-37404.)
compileall¶
Added new possibility to use hardlinks for duplicated .pyc
files: hardlink_dupes parameter and –hardlink-dupes command line option.
(Contributed by Lumír ‘Frenzy’ Balhar in bpo-40495.)
Added new options for path manipulation in resulting .pyc
files: stripdir, prependdir, limit_sl_dest parameters and -s, -p, -e command line options.
Added the possibility to specify the option for an optimization level multiple times.
(Contributed by Lumír ‘Frenzy’ Balhar in bpo-38112.)
concurrent.futures¶
Added a new cancel_futures parameter to
concurrent.futures.Executor.shutdown()
that cancels all pending futures
which have not started running, instead of waiting for them to complete before
shutting down the executor.
(Contributed by Kyle Stanley in bpo-39349.)
Removed daemon threads from ThreadPoolExecutor
and ProcessPoolExecutor
. This improves
compatibility with subinterpreters and predictability in their shutdown
processes. (Contributed by Kyle Stanley in bpo-39812.)
Workers in ProcessPoolExecutor
are now spawned on
demand, only when there are no available idle workers to reuse. This optimizes
startup overhead and reduces the amount of lost CPU time to idle workers.
(Contributed by Kyle Stanley in bpo-39207.)
curses¶
Added curses.get_escdelay()
, curses.set_escdelay()
,
curses.get_tabsize()
, and curses.set_tabsize()
functions.
(Contributed by Anthony Sottile in bpo-38312.)
datetime¶
The isocalendar()
of datetime.date
and isocalendar()
of datetime.datetime
methods now returns a namedtuple()
instead of a tuple
.
(Contributed by Donghee Na in bpo-24416.)
distutils¶
The upload command now creates SHA2-256 and Blake2b-256 hash digests. It skips MD5 on platforms that block MD5 digest. (Contributed by Christian Heimes in bpo-40698.)
fcntl¶
Added constants fcntl.F_OFD_GETLK
, fcntl.F_OFD_SETLK
and fcntl.F_OFD_SETLKW
.
(Contributed by Donghee Na in bpo-38602.)
ftplib¶
FTP
and FTP_TLS
now raise a ValueError
if the given timeout for their constructor is zero to prevent the creation of
a non-blocking socket. (Contributed by Donghee Na in bpo-39259.)
gc¶
When the garbage collector makes a collection in which some objects resurrect (they are reachable from outside the isolated cycles after the finalizers have been executed), do not block the collection of all objects that are still unreachable. (Contributed by Pablo Galindo and Tim Peters in bpo-38379.)
Added a new function gc.is_finalized()
to check if an object has been
finalized by the garbage collector. (Contributed by Pablo Galindo in
bpo-39322.)
hashlib¶
The hashlib
module can now use SHA3 hashes and SHAKE XOF from OpenSSL
when available.
(Contributed by Christian Heimes in bpo-37630.)
Builtin hash modules can now be disabled with
./configure --without-builtin-hashlib-hashes
or selectively enabled with
e.g. ./configure --with-builtin-hashlib-hashes=sha3,blake2
to force use
of OpenSSL based implementation.
(Contributed by Christian Heimes in bpo-40479)
http¶
HTTP status codes 103 EARLY_HINTS
, 418 IM_A_TEAPOT
and 425 TOO_EARLY
are added to
http.HTTPStatus
. (Contributed by Donghee Na in bpo-39509 and Ross Rhodes in bpo-39507.)
IDLE and idlelib¶
Added 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.)
Added keywords to module name completion list. (Contributed by Terry J. Reedy in bpo-37765.)
New in 3.9 maintenance releases
Make IDLE invoke sys.excepthook()
(when started without ‘-n’).
User hooks were previously ignored. (Contributed by Ken Hilton in
bpo-43008.)
The changes above have been backported to 3.8 maintenance releases.
Rearrange the settings dialog. Split the General tab into Windows and Shell/Ed tabs. Move help sources, which extend the Help menu, to the Extensions tab. Make space for new options and shorten the dialog. The latter makes the dialog better fit small screens. (Contributed by Terry Jan Reedy in bpo-40468.) Move the indent space setting from the Font tab to the new Windows tab. (Contributed by Mark Roseman and Terry Jan Reedy in bpo-33962.)
Apply syntax highlighting to .pyi
files. (Contributed by Alex
Waygood and Terry Jan Reedy in bpo-45447.)
imaplib¶
IMAP4
and IMAP4_SSL
now have
an optional timeout parameter for their constructors.
Also, the open()
method now has an optional timeout parameter
with this change. The overridden methods of IMAP4_SSL
and
IMAP4_stream
were applied to this change.
(Contributed by Donghee Na in bpo-38615.)
imaplib.IMAP4.unselect()
is added.
imaplib.IMAP4.unselect()
frees server’s resources associated with the
selected mailbox and returns the server to the authenticated
state. This command performs the same actions as imaplib.IMAP4.close()
, except
that no messages are permanently removed from the currently
selected mailbox. (Contributed by Donghee Na in bpo-40375.)
importlib¶
To improve consistency with import statements, importlib.util.resolve_name()
now raises ImportError
instead of ValueError
for invalid relative
import attempts.
(Contributed by Ngalim Siregar in bpo-37444.)
Import loaders which publish immutable module objects can now publish immutable packages in addition to individual modules. (Contributed by Dino Viehland in bpo-39336.)
Added importlib.resources.files()
function with support for
subdirectories in package data, matching backport in importlib_resources
version 1.5.
(Contributed by Jason R. Coombs in bpo-39791.)
Refreshed importlib.metadata
from importlib_metadata
version 1.6.1.
inspect¶
inspect.BoundArguments.arguments
is changed from OrderedDict
to regular
dict. (Contributed by Inada Naoki in bpo-36350 and bpo-39775.)
ipaddress¶
ipaddress
now supports IPv6 Scoped Addresses (IPv6 address with suffix %<scope_id>
).
Scoped IPv6 addresses can be parsed using ipaddress.IPv6Address
.
If present, scope zone ID is available through the scope_id
attribute.
(Contributed by Oleksandr Pavliuk in bpo-34788.)
Starting with Python 3.9.5 the ipaddress
module no longer
accepts any leading zeros in IPv4 address strings.
(Contributed by Christian Heimes in bpo-36384).
math¶
Expanded the math.gcd()
function to handle multiple arguments.
Formerly, it only supported two arguments.
(Contributed by Serhiy Storchaka in bpo-39648.)
Added math.lcm()
: return the least common multiple of specified arguments.
(Contributed by Mark Dickinson, Ananthakrishnan and Serhiy Storchaka in
bpo-39479 and bpo-39648.)
Added math.nextafter()
: return the next floating-point value after x
towards y.
(Contributed by Victor Stinner in bpo-39288.)
Added math.ulp()
: return the value of the least significant bit
of a float.
(Contributed by Victor Stinner in bpo-39310.)
multiprocessing¶
The multiprocessing.SimpleQueue
class has a new
close()
method to explicitly close the
queue.
(Contributed by Victor Stinner in bpo-30966.)
nntplib¶
NNTP
and NNTP_SSL
now raise a ValueError
if the given timeout for their constructor is zero to prevent the creation of
a non-blocking socket. (Contributed by Donghee Na in bpo-39259.)
os¶
Added CLD_KILLED
and CLD_STOPPED
for si_code
.
(Contributed by Donghee Na in bpo-38493.)
Exposed the Linux-specific os.pidfd_open()
(bpo-38692) and
os.P_PIDFD
(bpo-38713) for process management with file
descriptors.
The os.unsetenv()
function is now also available on Windows.
(Contributed by Victor Stinner in bpo-39413.)
The os.putenv()
and os.unsetenv()
functions are now always
available.
(Contributed by Victor Stinner in bpo-39395.)
Added os.waitstatus_to_exitcode()
function:
convert a wait status to an exit code.
(Contributed by Victor Stinner in bpo-40094.)
pathlib¶
Added pathlib.Path.readlink()
which acts similarly to
os.readlink()
.
(Contributed by Girts Folkmanis in bpo-30618)
pdb¶
On Windows now Pdb
supports ~/.pdbrc
.
(Contributed by Tim Hopper and Dan Lidral-Porter in bpo-20523.)
poplib¶
POP3
and POP3_SSL
now raise a ValueError
if the given timeout for their constructor is zero to prevent the creation of
a non-blocking socket. (Contributed by Donghee Na in bpo-39259.)
pprint¶
pprint
can now pretty-print types.SimpleNamespace
.
(Contributed by Carl Bordum Hansen in bpo-37376.)
pydoc¶
The documentation string is now shown not only for class, function,
method etc, but for any object that has its own __doc__
attribute.
(Contributed by Serhiy Storchaka in bpo-40257.)
random¶
Added a new random.Random.randbytes()
method: generate random bytes.
(Contributed by Victor Stinner in bpo-40286.)
signal¶
Exposed the Linux-specific signal.pidfd_send_signal()
for sending to
signals to a process using a file descriptor instead of a pid. (bpo-38712)
smtplib¶
SMTP
and SMTP_SSL
now raise a ValueError
if the given timeout for their constructor is zero to prevent the creation of
a non-blocking socket. (Contributed by Donghee Na in bpo-39259.)
LMTP
constructor now has an optional timeout parameter.
(Contributed by Donghee Na in bpo-39329.)
socket¶
The socket
module now exports the CAN_RAW_JOIN_FILTERS
constant on Linux 4.1 and greater.
(Contributed by Stefan Tatschner and Zackery Spytz in bpo-25780.)
The socket module now supports the CAN_J1939
protocol on
platforms that support it. (Contributed by Karl Ding in bpo-40291.)
The socket module now has the socket.send_fds()
and
socket.recv_fds()
functions. (Contributed by Joannah Nanjekye, Shinya
Okano and Victor Stinner in bpo-28724.)
time¶
On AIX, thread_time()
is now implemented with thread_cputime()
which has nanosecond resolution, rather than
clock_gettime(CLOCK_THREAD_CPUTIME_ID)
which has a resolution of 10 milliseconds.
(Contributed by Batuhan Taskaya in bpo-40192)
sys¶
Added a new sys.platlibdir
attribute: name of the platform-specific
library directory. It is used to build the path of standard library and the
paths of installed extension modules. It is equal to "lib"
on most
platforms. On Fedora and SuSE, it is equal to "lib64"
on 64-bit platforms.
(Contributed by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner in bpo-1294959.)
Previously, sys.stderr
was block-buffered when non-interactive. Now
stderr
defaults to always being line-buffered.
(Contributed by Jendrik Seipp in bpo-13601.)
tracemalloc¶
Added tracemalloc.reset_peak()
to set the peak size of traced memory
blocks to the current size, to measure the peak of specific pieces of code.
(Contributed by Huon Wilson in bpo-40630.)
typing¶
PEP 593 introduced an typing.Annotated
type to decorate existing
types with context-specific metadata and new include_extras
parameter to
typing.get_type_hints()
to access the metadata at runtime. (Contributed
by Till Varoquaux and Konstantin Kashin.)
unicodedata¶
The Unicode database has been updated to version 13.0.0. (bpo-39926).
venv¶
The activation scripts provided by venv
now all specify their prompt
customization consistently by always using the value specified by
__VENV_PROMPT__
. Previously some scripts unconditionally used
__VENV_PROMPT__
, others only if it happened to be set (which was the default
case), and one used __VENV_NAME__
instead.
(Contributed by Brett Cannon in bpo-37663.)
xml¶
White space characters within attributes are now preserved when serializing
xml.etree.ElementTree
to XML file. EOLNs are no longer normalized
to “n”. This is the result of discussion about how to interpret
section 2.11 of XML spec.
(Contributed by Mefistotelis in bpo-39011.)
Optimizations¶
Optimized the idiom for assignment a temporary variable in comprehensions. Now
for y in [expr]
in comprehensions is as fast as a simple assignmenty = expr
. For example:sums = [s for s in [0] for x in data for s in [s + x]]
Unlike the
:=
operator this idiom does not leak a variable to the outer scope.(Contributed by Serhiy Storchaka in bpo-32856.)
Optimized signal handling in multithreaded applications. If a thread different than the main thread gets a signal, the bytecode evaluation loop is no longer interrupted at each bytecode instruction to check for pending signals which cannot be handled. Only the main thread of the main interpreter can handle signals.
Previously, the bytecode evaluation loop was interrupted at each instruction until the main thread handles signals. (Contributed by Victor Stinner in bpo-40010.)
Optimized the
subprocess
module on FreeBSD usingclosefrom()
. (Contributed by Ed Maste, Conrad Meyer, Kyle Evans, Kubilay Kocak and Victor Stinner in bpo-38061.)PyLong_FromDouble()
is now up to 1.87x faster for values that fit into long. (Contributed by Sergey Fedoseev in bpo-37986.)A number of Python builtins (
range
,tuple
,set
,frozenset
,list
,dict
) are now sped up by using PEP 590 vectorcall protocol. (Contributed by Donghee Na, Mark Shannon, Jeroen Demeyer and Petr Viktorin in bpo-37207.)Optimized
set.difference_update()
for the case when the other set is much larger than the base set. (Suggested by Evgeny Kapun with code contributed by Michele Orrù in bpo-8425.)Python’s small object allocator (
obmalloc.c
) now allows (no more than) one empty arena to remain available for immediate reuse, without returning it to the OS. This prevents thrashing in simple loops where an arena could be created and destroyed anew on each iteration. (Contributed by Tim Peters in bpo-37257.)floor division of float operation now has a better performance. Also the message of
ZeroDivisionError
for this operation is updated. (Contributed by Donghee Na in bpo-39434.)Decoding short ASCII strings with UTF-8 and ascii codecs is now about 15% faster. (Contributed by Inada Naoki in bpo-37348.)
Here’s a summary of performance improvements from Python 3.4 through Python 3.9:
Python version 3.4 3.5 3.6 3.7 3.8 3.9
-------------- --- --- --- --- --- ---
Variable and attribute read access:
read_local 7.1 7.1 5.4 5.1 3.9 3.9
read_nonlocal 7.1 8.1 5.8 5.4 4.4 4.5
read_global 15.5 19.0 14.3 13.6 7.6 7.8
read_builtin 21.1 21.6 18.5 19.0 7.5 7.8
read_classvar_from_class 25.6 26.5 20.7 19.5 18.4 17.9
read_classvar_from_instance 22.8 23.5 18.8 17.1 16.4 16.9
read_instancevar 32.4 33.1 28.0 26.3 25.4 25.3
read_instancevar_slots 27.8 31.3 20.8 20.8 20.2 20.5
read_namedtuple 73.8 57.5 45.0 46.8 18.4 18.7
read_boundmethod 37.6 37.9 29.6 26.9 27.7 41.1
Variable and attribute write access:
write_local 8.7 9.3 5.5 5.3 4.3 4.3
write_nonlocal 10.5 11.1 5.6 5.5 4.7 4.8
write_global 19.7 21.2 18.0 18.0 15.8 16.7
write_classvar 92.9 96.0 104.6 102.1 39.2 39.8
write_instancevar 44.6 45.8 40.0 38.9 35.5 37.4
write_instancevar_slots 35.6 36.1 27.3 26.6 25.7 25.8
Data structure read access:
read_list 24.2 24.5 20.8 20.8 19.0 19.5
read_deque 24.7 25.5 20.2 20.6 19.8 20.2
read_dict 24.3 25.7 22.3 23.0 21.0 22.4
read_strdict 22.6 24.3 19.5 21.2 18.9 21.5
Data structure write access:
write_list 27.1 28.5 22.5 21.6 20.0 20.0
write_deque 28.7 30.1 22.7 21.8 23.5 21.7
write_dict 31.4 33.3 29.3 29.2 24.7 25.4
write_strdict 28.4 29.9 27.5 25.2 23.1 24.5
Stack (or queue) operations:
list_append_pop 93.4 112.7 75.4 74.2 50.8 50.6
deque_append_pop 43.5 57.0 49.4 49.2 42.5 44.2
deque_append_popleft 43.7 57.3 49.7 49.7 42.8 46.4
Timing loop:
loop_overhead 0.5 0.6 0.4 0.3 0.3 0.3
These results were generated from the variable access benchmark script at:
Tools/scripts/var_access_benchmark.py
. The benchmark script displays timings
in nanoseconds. The benchmarks were measured on an
Intel® Core™ i7-4960HQ processor
running the macOS 64-bit builds found at
python.org.
Deprecated¶
The distutils
bdist_msi
command is now deprecated, usebdist_wheel
(wheel packages) instead. (Contributed by Hugo van Kemenade in bpo-39586.)Currently
math.factorial()
acceptsfloat
instances with non-negative integer values (like5.0
). It raises aValueError
for non-integral and negative floats. It is now deprecated. In future Python versions it will raise aTypeError
for all floats. (Contributed by Serhiy Storchaka in bpo-37315.)The
parser
andsymbol
modules are deprecated and will be removed in future versions of Python. For the majority of use cases, users can leverage the Abstract Syntax Tree (AST) generation and compilation stage, using theast
module.The Public C API functions
PyParser_SimpleParseStringFlags()
,PyParser_SimpleParseStringFlagsFilename()
,PyParser_SimpleParseFileFlags()
andPyNode_Compile()
are deprecated and will be removed in Python 3.10 together with the old parser.Using
NotImplemented
in a boolean context has been deprecated, as it is almost exclusively the result of incorrect rich comparator implementations. It will be made aTypeError
in a future version of Python. (Contributed by Josh Rosenberg in bpo-35712.)The
random
module currently accepts any hashable type as a possible seed value. Unfortunately, some of those types are not guaranteed to have a deterministic hash value. After Python 3.9, the module will restrict its seeds toNone
,int
,float
,str
,bytes
, andbytearray
.Opening the
GzipFile
file for writing without specifying the mode argument is deprecated. In future Python versions it will always be opened for reading by default. Specify the mode argument for opening it for writing and silencing a warning. (Contributed by Serhiy Storchaka in bpo-28286.)Deprecated the
split()
method of_tkinter.TkappType
in favour of thesplitlist()
method which has more consistent and predictable behavior. (Contributed by Serhiy Storchaka in bpo-38371.)The explicit passing of coroutine objects to
asyncio.wait()
has been deprecated and will be removed in version 3.11. (Contributed by Yury Selivanov and Kyle Stanley in bpo-34790.)binhex4 and hexbin4 standards are now deprecated. The
binhex
module and the followingbinascii
functions are now deprecated:b2a_hqx()
,a2b_hqx()
rlecode_hqx()
,rledecode_hqx()
(Contributed by Victor Stinner in bpo-39353.)
ast
classesslice
,Index
andExtSlice
are considered deprecated and will be removed in future Python versions.value
itself should be used instead ofIndex(value)
.Tuple(slices, Load())
should be used instead ofExtSlice(slices)
. (Contributed by Serhiy Storchaka in bpo-34822.)ast
classesSuite
,Param
,AugLoad
andAugStore
are considered deprecated and will be removed in future Python versions. They were not generated by the parser and not accepted by the code generator in Python 3. (Contributed by Batuhan Taskaya in bpo-39639 and bpo-39969 and Serhiy Storchaka in bpo-39988.)The
PyEval_InitThreads()
andPyEval_ThreadsInitialized()
functions are now deprecated and will be removed in Python 3.11. CallingPyEval_InitThreads()
now does nothing. The GIL is initialized byPy_Initialize()
since Python 3.7. (Contributed by Victor Stinner in bpo-39877.)Passing
None
as the first argument to theshlex.split()
function has been deprecated. (Contributed by Zackery Spytz in bpo-33262.)smtpd.MailmanProxy()
is now deprecated as it is unusable without an external module,mailman
. (Contributed by Samuel Colvin in bpo-35800.)The
lib2to3
module now emits aPendingDeprecationWarning
. Python 3.9 switched to a PEG parser (see PEP 617), and Python 3.10 may include new language syntax that is not parsable by lib2to3’s LL(1) parser. Thelib2to3
module may be removed from the standard library in a future Python version. Consider third-party alternatives such as LibCST or parso. (Contributed by Carl Meyer in bpo-40360.)The random parameter of
random.shuffle()
has been deprecated. (Contributed by Raymond Hettinger in bpo-40465)
Removed¶
The erroneous version at
unittest.mock.__version__
has been removed.nntplib.NNTP
:xpath()
andxgtitle()
methods have been removed. These methods are deprecated since Python 3.3. Generally, these extensions are not supported or not enabled by NNTP server administrators. Forxgtitle()
, please usenntplib.NNTP.descriptions()
ornntplib.NNTP.description()
instead. (Contributed by Donghee Na in bpo-39366.)array.array
:tostring()
andfromstring()
methods have been removed. They were aliases totobytes()
andfrombytes()
, deprecated since Python 3.2. (Contributed by Victor Stinner in bpo-38916.)The undocumented
sys.callstats()
function has been removed. Since Python 3.7, it was deprecated and always returnedNone
. It required a special build optionCALL_PROFILE
which was already removed in Python 3.7. (Contributed by Victor Stinner in bpo-37414.)The
sys.getcheckinterval()
andsys.setcheckinterval()
functions have been removed. They were deprecated since Python 3.2. Usesys.getswitchinterval()
andsys.setswitchinterval()
instead. (Contributed by Victor Stinner in bpo-37392.)The C function
PyImport_Cleanup()
has been removed. It was documented as: “Empty the module table. For internal use only.” (Contributed by Victor Stinner in bpo-36710.)_dummy_thread
anddummy_threading
modules have been removed. These modules were deprecated since Python 3.7 which requires threading support. (Contributed by Victor Stinner in bpo-37312.)aifc.openfp()
alias toaifc.open()
,sunau.openfp()
alias tosunau.open()
, andwave.openfp()
alias towave.open()
have been removed. They were deprecated since Python 3.7. (Contributed by Victor Stinner in bpo-37320.)The
isAlive()
method ofthreading.Thread
has been removed. It was deprecated since Python 3.8. Useis_alive()
instead. (Contributed by Donghee Na in bpo-37804.)Methods
getchildren()
andgetiterator()
of classesElementTree
andElement
in theElementTree
module have been removed. They were deprecated in Python 3.2. Useiter(x)
orlist(x)
instead ofx.getchildren()
andx.iter()
orlist(x.iter())
instead ofx.getiterator()
. (Contributed by Serhiy Storchaka in bpo-36543.)The old
plistlib
API has been removed, it was deprecated since Python 3.4. Use theload()
,loads()
,dump()
, anddumps()
functions. Additionally, the use_builtin_types parameter was removed, standardbytes
objects are always used instead. (Contributed by Jon Janzen in bpo-36409.)The C function
PyGen_NeedsFinalizing
has been removed. It was not documented, tested, or used anywhere within CPython after the implementation of PEP 442. Patch by Joannah Nanjekye. (Contributed by Joannah Nanjekye in bpo-15088)base64.encodestring()
andbase64.decodestring()
, aliases deprecated since Python 3.1, have been removed: usebase64.encodebytes()
andbase64.decodebytes()
instead. (Contributed by Victor Stinner in bpo-39351.)fractions.gcd()
function has been removed, it was deprecated since Python 3.5 (bpo-22486): usemath.gcd()
instead. (Contributed by Victor Stinner in bpo-39350.)The buffering parameter of
bz2.BZ2File
has been removed. Since Python 3.0, it was ignored and using it emitted aDeprecationWarning
. Pass an open file object to control how the file is opened. (Contributed by Victor Stinner in bpo-39357.)The encoding parameter of
json.loads()
has been removed. As of Python 3.1, it was deprecated and ignored; using it has emitted aDeprecationWarning
since Python 3.8. (Contributed by Inada Naoki in bpo-39377)with (await asyncio.lock):
andwith (yield from asyncio.lock):
statements are not longer supported, useasync with lock
instead. The same is correct forasyncio.Condition
andasyncio.Semaphore
. (Contributed by Andrew Svetlov in bpo-34793.)The
sys.getcounts()
function, the-X showalloccount
command line option and theshow_alloc_count
field of the C structurePyConfig
have been removed. They required a special Python build by definingCOUNT_ALLOCS
macro. (Contributed by Victor Stinner in bpo-39489.)The
_field_types
attribute of thetyping.NamedTuple
class has been removed. It was deprecated since Python 3.8. Use the__annotations__
attribute instead. (Contributed by Serhiy Storchaka in bpo-40182.)The
symtable.SymbolTable.has_exec()
method has been removed. It was deprecated since 2006, and only returningFalse
when it’s called. (Contributed by Batuhan Taskaya in bpo-40208)The
asyncio.Task.current_task()
andasyncio.Task.all_tasks()
have been removed. They were deprecated since Python 3.7 and you can useasyncio.current_task()
andasyncio.all_tasks()
instead. (Contributed by Rémi Lapeyre in bpo-40967)The
unescape()
method in thehtml.parser.HTMLParser
class has been removed (it was deprecated since Python 3.4).html.unescape()
should be used for converting character references to the corresponding unicode characters.
Porting to Python 3.9¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Changes in the Python API¶
__import__()
andimportlib.util.resolve_name()
now raiseImportError
where it previously raisedValueError
. Callers catching the specific exception type and supporting both Python 3.9 and earlier versions will need to catch both usingexcept (ImportError, ValueError):
.The
venv
activation scripts no longer special-case when__VENV_PROMPT__
is set to""
.The
select.epoll.unregister()
method no longer ignores theEBADF
error. (Contributed by Victor Stinner in bpo-39239.)The compresslevel parameter of
bz2.BZ2File
became keyword-only, since the buffering parameter has been removed. (Contributed by Victor Stinner in bpo-39357.)Simplified AST for subscription. Simple indices will be represented by their value, extended slices will be represented as tuples.
Index(value)
will return avalue
itself,ExtSlice(slices)
will returnTuple(slices, Load())
. (Contributed by Serhiy Storchaka in bpo-34822.)The
importlib
module now ignores thePYTHONCASEOK
environment variable when the-E
or-I
command line options are being used.The encoding parameter has been added to the classes
ftplib.FTP
andftplib.FTP_TLS
as a keyword-only parameter, and the default encoding is changed from Latin-1 to UTF-8 to follow RFC 2640.asyncio.loop.shutdown_default_executor()
has been added toAbstractEventLoop
, meaning alternative event loops that inherit from it should have this method defined. (Contributed by Kyle Stanley in bpo-34037.)The constant values of future flags in the
__future__
module is updated in order to prevent collision with compiler flags. PreviouslyPyCF_ALLOW_TOP_LEVEL_AWAIT
was clashing withCO_FUTURE_DIVISION
. (Contributed by Batuhan Taskaya in bpo-39562)array('u')
now useswchar_t
as C type instead ofPy_UNICODE
. This change doesn’t affect to its behavior becausePy_UNICODE
is alias ofwchar_t
since Python 3.3. (Contributed by Inada Naoki in bpo-34538.)The
logging.getLogger()
API now returns the root logger when passed the name'root'
, whereas previously it returned a non-root logger named'root'
. This could affect cases where user code explicitly wants a non-root logger named'root'
, or instantiates a logger usinglogging.getLogger(__name__)
in some top-level module called'root.py'
. (Contributed by Vinay Sajip in bpo-37742.)Division handling of
PurePath
now returnsNotImplemented
instead of raising aTypeError
when passed something other than an instance ofstr
orPurePath
. This allows creating compatible classes that don’t inherit from those mentioned types. (Contributed by Roger Aiudi in bpo-34775).Starting with Python 3.9.5 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 functionsocket.inet_aton()
treats leading zeros as octal notatation. glibc implementation of moderninet_pton()
does not accept any leading zeros. (Contributed by Christian Heimes in bpo-36384).codecs.lookup()
now normalizes the encoding name the same way asencodings.normalize_encoding()
, except thatcodecs.lookup()
also converts the name to lower case. For example,"latex+latin1"
encoding name is now normalized to"latex_latin1"
. (Contributed by Jordon Xu in bpo-37751.)
Changes in the C API¶
Instances of heap-allocated types (such as those created with
PyType_FromSpec()
and similar APIs) hold a reference to their type object since Python 3.8. As indicated in the “Changes in the C API” of Python 3.8, for the vast majority of cases, there should be no side effect but for types that have a customtp_traverse
function, ensure that all customtp_traverse
functions of heap-allocated types visit the object’s type.Example:
int foo_traverse(PyObject *self, visitproc visit, void *arg) { // Rest of the traverse function #if PY_VERSION_HEX >= 0x03090000 // This was not needed before Python 3.9 (Python issue 35810 and 40217) Py_VISIT(Py_TYPE(self)); #endif }
If your traverse function delegates to
tp_traverse
of its base class (or another type), ensure thatPy_TYPE(self)
is visited only once. Note that only heap type are expected to visit the type intp_traverse
.For example, if your
tp_traverse
function includes:base->tp_traverse(self, visit, arg)
then add:
#if PY_VERSION_HEX >= 0x03090000 // This was not needed before Python 3.9 (bpo-35810 and bpo-40217) if (base->tp_flags & Py_TPFLAGS_HEAPTYPE) { // a heap type's tp_traverse already visited Py_TYPE(self) } else { Py_VISIT(Py_TYPE(self)); } #else
The functions
PyEval_CallObject
,PyEval_CallFunction
,PyEval_CallMethod
andPyEval_CallObjectWithKeywords
are deprecated. UsePyObject_Call()
and its variants instead. (See more details in bpo-29548.)
CPython bytecode changes¶
The
LOAD_ASSERTION_ERROR
opcode was added for handling theassert
statement. Previously, the assert statement would not work correctly if theAssertionError
exception was being shadowed. (Contributed by Zackery Spytz in bpo-34880.)The
COMPARE_OP
opcode was split into four distinct instructions:COMPARE_OP
for rich comparisonsIS_OP
for ‘is’ and ‘is not’ testsCONTAINS_OP
for ‘in’ and ‘not in’ testsJUMP_IF_NOT_EXC_MATCH
for checking exceptions in ‘try-except’ statements.
(Contributed by Mark Shannon in bpo-39156.)
Build Changes¶
Added
--with-platlibdir
option to theconfigure
script: name of the platform-specific library directory, stored in the newsys.platlibdir
attribute. Seesys.platlibdir
attribute for more information. (Contributed by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner in bpo-1294959.)The
COUNT_ALLOCS
special build macro has been removed. (Contributed by Victor Stinner in bpo-39489.)On non-Windows platforms, the
setenv()
andunsetenv()
functions are now required to build Python. (Contributed by Victor Stinner in bpo-39395.)On non-Windows platforms, creating
bdist_wininst
installers is now officially unsupported. (See bpo-10945 for more details.)When building Python on macOS from source,
_tkinter
now links with non-system Tcl and Tk frameworks if they are installed in/Library/Frameworks
, as had been the case on older releases of macOS. If a macOS SDK is explicitly configured, by using--enable-universalsdk
or-isysroot
, only the SDK itself is searched. The default behavior can still be overridden with--with-tcltk-includes
and--with-tcltk-libs
. (Contributed by Ned Deily in bpo-34956.)Python can now be built for Windows 10 ARM64. (Contributed by Steve Dower in bpo-33125.)
Some individual tests are now skipped when
--pgo
is used. The tests in question increased the PGO task time significantly and likely didn’t help improve optimization of the final executable. This speeds up the task by a factor of about 15x. Running the full unit test suite is slow. This change may result in a slightly less optimized build since not as many code branches will be executed. If you are willing to wait for the much slower build, the old behavior can be restored using./configure [..] PROFILE_TASK="-m test --pgo-extended"
. We make no guarantees as to which PGO task set produces a faster build. Users who care should run their own relevant benchmarks as results can depend on the environment, workload, and compiler tool chain. (See bpo-36044 and bpo-37707 for more details.)
C API Changes¶
New Features¶
PEP 573: Added
PyType_FromModuleAndSpec()
to associate a module with a class;PyType_GetModule()
andPyType_GetModuleState()
to retrieve the module and its state; andPyCMethod
andMETH_METHOD
to allow a method to access the class it was defined in. (Contributed by Marcel Plch and Petr Viktorin in bpo-38787.)Added
PyFrame_GetCode()
function: get a frame code. AddedPyFrame_GetBack()
function: get the frame next outer frame. (Contributed by Victor Stinner in bpo-40421.)Added
PyFrame_GetLineNumber()
to the limited C API. (Contributed by Victor Stinner in bpo-40421.)Added
PyThreadState_GetInterpreter()
andPyInterpreterState_Get()
functions to get the interpreter. AddedPyThreadState_GetFrame()
function to get the current frame of a Python thread state. AddedPyThreadState_GetID()
function: get the unique identifier of a Python thread state. (Contributed by Victor Stinner in bpo-39947.)Added a new public
PyObject_CallNoArgs()
function to the C API, which calls a callable Python object without any arguments. It is the most efficient way to call a callable Python object without any argument. (Contributed by Victor Stinner in bpo-37194.)Changes in the limited C API (if
Py_LIMITED_API
macro is defined):Provide
Py_EnterRecursiveCall()
andPy_LeaveRecursiveCall()
as regular functions for the limited API. Previously, there were defined as macros, but these macros didn’t compile with the limited C API which cannot accessPyThreadState.recursion_depth
field (the structure is opaque in the limited C API).PyObject_INIT()
andPyObject_INIT_VAR()
become regular “opaque” function to hide implementation details.
The
PyModule_AddType()
function is added to help adding a type to a module. (Contributed by Donghee Na in bpo-40024.)Added the functions
PyObject_GC_IsTracked()
andPyObject_GC_IsFinalized()
to the public API to allow to query if Python objects are being currently tracked or have been already finalized by the garbage collector respectively. (Contributed by Pablo Galindo Salgado in bpo-40241.)Added
_PyObject_FunctionStr()
to get a user-friendly string representation of a function-like object. (Patch by Jeroen Demeyer in bpo-37645.)Added
PyObject_CallOneArg()
for calling an object with one positional argument (Patch by Jeroen Demeyer in bpo-37483.)
Porting to Python 3.9¶
PyInterpreterState.eval_frame
(PEP 523) now requires a new mandatory tstate parameter (PyThreadState*
). (Contributed by Victor Stinner in bpo-38500.)Extension modules:
m_traverse
,m_clear
andm_free
functions ofPyModuleDef
are no longer called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed (Py_mod_exec
function). More precisely, these functions are not called ifm_size
is greater than 0 and the module state (as returned byPyModule_GetState()
) isNULL
.Extension modules without module state (
m_size <= 0
) are not affected.If
Py_AddPendingCall()
is called in a subinterpreter, the function is now scheduled to be called from the subinterpreter, rather than being called from the main interpreter. Each subinterpreter now has its own list of scheduled calls. (Contributed by Victor Stinner in bpo-39984.)The Windows registry is no longer used to initialize
sys.path
when the-E
option is used (ifPyConfig.use_environment
is set to0
). This is significant when embedding Python on Windows. (Contributed by Zackery Spytz in bpo-8901.)The global variable
PyStructSequence_UnnamedField
is now a constant and refers to a constant string. (Contributed by Serhiy Storchaka in bpo-38650.)The
PyGC_Head
structure is now opaque. It is only defined in the internal C API (pycore_gc.h
). (Contributed by Victor Stinner in bpo-40241.)The
Py_UNICODE_COPY
,Py_UNICODE_FILL
,PyUnicode_WSTR_LENGTH
,PyUnicode_FromUnicode()
,PyUnicode_AsUnicode()
,_PyUnicode_AsUnicode
, andPyUnicode_AsUnicodeAndSize()
are marked as deprecated in C. They have been deprecated by PEP 393 since Python 3.3. (Contributed by Inada Naoki in bpo-36346.)The
Py_FatalError()
function is replaced with a macro which logs automatically the name of the current function, unless thePy_LIMITED_API
macro is defined. (Contributed by Victor Stinner in bpo-39882.)The vectorcall protocol now requires that the caller passes only strings as keyword names. (See bpo-37540 for more information.)
Implementation details of a number of macros and functions are now hidden:
PyObject_IS_GC()
macro was converted to a function.The
PyObject_NEW()
macro becomes an alias to thePyObject_New
macro, and thePyObject_NEW_VAR()
macro becomes an alias to thePyObject_NewVar
macro. They no longer access directly thePyTypeObject.tp_basicsize
member.PyObject_GET_WEAKREFS_LISTPTR()
macro was converted to a function: the macro accessed directly thePyTypeObject.tp_weaklistoffset
member.PyObject_CheckBuffer()
macro was converted to a function: the macro accessed directly thePyTypeObject.tp_as_buffer
member.PyIndex_Check()
is now always declared as an opaque function to hide implementation details: removed thePyIndex_Check()
macro. The macro accessed directly thePyTypeObject.tp_as_number
member.
(See bpo-40170 for more details.)
Removed¶
Excluded
PyFPE_START_PROTECT()
andPyFPE_END_PROTECT()
macros ofpyfpe.h
from the limited C API. (Contributed by Victor Stinner in bpo-38835.)The
tp_print
slot of PyTypeObject has been removed. It was used for printing objects to files in Python 2.7 and before. Since Python 3.0, it has been ignored and unused. (Contributed by Jeroen Demeyer in bpo-36974.)Changes in the limited C API (if
Py_LIMITED_API
macro is defined):Excluded the following functions from the limited C API:
PyThreadState_DeleteCurrent()
(Contributed by Joannah Nanjekye in bpo-37878.)_Py_CheckRecursionLimit
_Py_NewReference()
_Py_ForgetReference()
_PyTraceMalloc_NewReference()
_Py_GetRefTotal()
The trashcan mechanism which never worked in the limited C API.
PyTrash_UNWIND_LEVEL
Py_TRASHCAN_BEGIN_CONDITION
Py_TRASHCAN_BEGIN
Py_TRASHCAN_END
Py_TRASHCAN_SAFE_BEGIN
Py_TRASHCAN_SAFE_END
Moved following functions and definitions to the internal C API:
_PyDebug_PrintTotalRefs()
_Py_PrintReferences()
_Py_PrintReferenceAddresses()
_Py_tracemalloc_config
_Py_AddToAllObjects()
(specific toPy_TRACE_REFS
build)
Removed
_PyRuntime.getframe
hook and removed_PyThreadState_GetFrame
macro which was an alias to_PyRuntime.getframe
. They were only exposed by the internal C API. Removed alsoPyThreadFrameGetter
type. (Contributed by Victor Stinner in bpo-39946.)Removed the following functions from the C API. Call
PyGC_Collect()
explicitly to clear all free lists. (Contributed by Inada Naoki and Victor Stinner in bpo-37340, bpo-38896 and bpo-40428.)PyAsyncGen_ClearFreeLists()
PyContext_ClearFreeList()
PyDict_ClearFreeList()
PyFloat_ClearFreeList()
PyFrame_ClearFreeList()
PyList_ClearFreeList()
PyMethod_ClearFreeList()
andPyCFunction_ClearFreeList()
: the free lists of bound method objects have been removed.PySet_ClearFreeList()
: the set free list has been removed in Python 3.4.PyTuple_ClearFreeList()
PyUnicode_ClearFreeList()
: the Unicode free list has been removed in Python 3.3.
Removed
_PyUnicode_ClearStaticStrings()
function. (Contributed by Victor Stinner in bpo-39465.)Removed
Py_UNICODE_MATCH
. It has been deprecated by PEP 393, and broken since Python 3.3. ThePyUnicode_Tailmatch()
function can be used instead. (Contributed by Inada Naoki in bpo-36346.)Cleaned header files of interfaces defined but with no implementation. The public API symbols being removed are:
_PyBytes_InsertThousandsGroupingLocale
,_PyBytes_InsertThousandsGrouping
,_Py_InitializeFromArgs
,_Py_InitializeFromWideArgs
,_PyFloat_Repr
,_PyFloat_Digits
,_PyFloat_DigitsInit
,PyFrame_ExtendStack
,_PyAIterWrapper_Type
,PyNullImporter_Type
,PyCmpWrapper_Type
,PySortWrapper_Type
,PyNoArgsFunction
. (Contributed by Pablo Galindo Salgado in bpo-39372.)
Notable changes in Python 3.9.1¶
typing¶
The behavior of typing.Literal
was changed to conform with PEP 586
and to match the behavior of static type checkers specified in the PEP.
Literal
now de-duplicates parameters.Equality comparisons between
Literal
objects are now order independent.Literal
comparisons now respect types. For example,Literal[0] == Literal[False]
previously evaluated toTrue
. It is nowFalse
. To support this change, the internally used type cache now supports differentiating types.Literal
objects will now raise aTypeError
exception during equality comparisons if any of their parameters are not hashable. Note that declaringLiteral
with mutable parameters will not throw an error:>>> from typing import Literal >>> Literal[{0}] >>> Literal[{0}] == Literal[{False}] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unhashable type: 'set'
(Contributed by Yurii Karabas in bpo-42345.)
macOS 11.0 (Big Sur) and Apple Silicon Mac support¶
As of 3.9.1, Python now fully supports building and running on macOS 11.0
(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. Binaries
can also now be built on current versions of macOS to be deployed on a range
of older macOS versions (tested to 10.9) while making some newer OS
functions and options conditionally available based on the operating system
version in use at runtime (“weaklinking”).
(Contributed by Ronald Oussoren and Lawrence D’Anna in bpo-41100.)
Notable changes in Python 3.9.2¶
collections.abc¶
collections.abc.Callable
generic now flattens type parameters, similar
to what typing.Callable
currently does. This means that
collections.abc.Callable[[int, str], str]
will have __args__
of
(int, str, str)
; previously this was ([int, str], str)
. To allow this
change, types.GenericAlias
can now be subclassed, and a subclass will
be returned when subscripting the collections.abc.Callable
type.
Code which accesses the arguments via typing.get_args()
or __args__
need to account for this change. A DeprecationWarning
may be emitted for
invalid forms of parameterizing collections.abc.Callable
which may have
passed silently in Python 3.9.1. This DeprecationWarning
will
become a TypeError
in Python 3.10.
(Contributed by Ken Jin in bpo-42195.)
urllib.parse¶
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 3.9.3¶
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 3.9.5¶
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 gh-88048)
Notable security feature in 3.9.14¶
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 3.9.17¶
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.)


File Objects

File Objects¶
These APIs are a minimal emulation of the Python 2 C API for built-in file
objects, which used to rely on the buffered I/O (FILE*) support
from the C standard library. In Python 3, files and streams use the new
io
module, which defines several layers over the low-level unbuffered
I/O of the operating system. The functions described below are
convenience C wrappers over these new APIs, and meant mostly for internal
error reporting in the interpreter; third-party code is advised to access
the io
APIs instead.
-
PyObject *PyFile_FromFd(int fd, const char *name, const char *mode, int buffering, const char *encoding, const char *errors, const char *newline, int closefd)¶
- Return value: New reference. Part of the Stable ABI.
Create a Python file object from the file descriptor of an already opened file fd. The arguments name, encoding, errors and newline can be
NULL
to use the defaults; buffering can be -1 to use the default. name is ignored and kept for backward compatibility. ReturnNULL
on failure. For a more comprehensive description of the arguments, please refer to theio.open()
function documentation.Warning
Since Python streams have their own buffering layer, mixing them with OS-level file descriptors can produce various issues (such as unexpected ordering of data).
Changed in version 3.2: Ignore name attribute.
-
int PyObject_AsFileDescriptor(PyObject *p)¶
- Part of the Stable ABI.
Return the file descriptor associated with p as an int. If the object is an integer, its value is returned. If not, the object’s
fileno()
method is called if it exists; the method must return an integer, which is returned as the file descriptor value. Sets an exception and returns-1
on failure.
-
PyObject *PyFile_GetLine(PyObject *p, int n)¶
- Return value: New reference. Part of the Stable ABI.
Equivalent to
p.readline([n])
, this function reads one line from the object p. p may be a file object or any object with areadline()
method. If n is0
, exactly one line is read, regardless of the length of the line. If n is greater than0
, no more than n bytes will be read from the file; a partial line can be returned. In both cases, an empty string is returned if the end of the file is reached immediately. If n is less than0
, however, one line is read regardless of length, butEOFError
is raised if the end of the file is reached immediately.
-
int PyFile_SetOpenCodeHook(Py_OpenCodeHookFunction handler)¶
Overrides the normal behavior of
io.open_code()
to pass its parameter through the provided handler.The handler is a function of type:
-
typedef PyObject *(*Py_OpenCodeHookFunction)(PyObject*, void*)¶
Equivalent of PyObject *(*)(PyObject *path, void *userData), where path is guaranteed to be
PyUnicodeObject
.
The userData pointer is passed into the hook function. Since hook functions may be called from different runtimes, this pointer should not refer directly to Python state.
As this hook is intentionally used during import, avoid importing new modules during its execution unless they are known to be frozen or available in
sys.modules
.Once a hook has been set, it cannot be removed or replaced, and later calls to
PyFile_SetOpenCodeHook()
will fail. On failure, the function returns -1 and sets an exception if the interpreter has been initialized.This function is safe to call before
Py_Initialize()
.Raises an auditing event
setopencodehook
with no arguments.Added in version 3.8.
-
typedef PyObject *(*Py_OpenCodeHookFunction)(PyObject*, void*)¶
-
PyObject *PyFile_OpenCodeObject(PyObject *path)¶
Open path with the mode
'rb'
. path must be a Pythonstr
object. The behavior of this function may be overridden byPyFile_SetOpenCodeHook()
to allow for some preprocessing of the text.This is analogous to
io.open_code()
in Python.On success, this function returns a strong reference to a Python file object. On failure, this function returns
NULL
with an exception set.Added in version 3.8.
-
PyObject *PyFile_OpenCode(const char *path)¶
Similar to
PyFile_OpenCodeObject()
, but path is a UTF-8 encoded const char*.Added in version 3.8.
-
int PyFile_WriteObject(PyObject *obj, PyObject *p, int flags)¶
- Part of the Stable ABI.
Write object obj to file object p. The only supported flag for flags is
Py_PRINT_RAW
; if given, thestr()
of the object is written instead of therepr()
. Return0
on success or-1
on failure; the appropriate exception will be set.
-
int PyFile_WriteString(const char *s, PyObject *p)¶
- Part of the Stable ABI.
Write string s to file object p. Return
0
on success or-1
on failure; the appropriate exception will be set.
Deprecated API¶
These are soft deprecated APIs that were included in Python’s C API
by mistake. They are documented solely for completeness; use other
PyFile*
APIs instead.
-
PyObject *PyFile_NewStdPrinter(int fd)¶
Use
PyFile_FromFd()
with defaults (fd, NULL, "w", -1, NULL, NULL, NULL, 0
) instead.
-
PyTypeObject PyStdPrinter_Type¶
Type of file-like objects used internally at Python startup when
io
is not yet available. Use Pythonopen()
orPyFile_FromFd()
to create file objects instead.


Unix-specific services

Unix-specific services¶
The modules described in this chapter provide interfaces to features that are unique to the Unix operating system, or in some cases to some or many variants of it. Here’s an overview:
shlex
— Simple lexical analysisposix
— The most common POSIX system callspwd
— The password databasegrp
— The group databasetermios
— POSIX style tty controltty
— Terminal control functionspty
— Pseudo-terminal utilitiesfcntl
— Thefcntl
andioctl
system callsresource
— Resource usage informationsyslog
— Unix syslog library routines