What’s New In Python 3.9 — Python documentation
What’s New In Python 3.9
- Release
- Date
- December 09, 2021
- Editor
- Łukasz Langa
This article explains the new features in Python 3.9, compared to 3.8. Python 3.9 was released on October 5th, 2020.
For full details, see the changelog.
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 :issue:`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 :issue:`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 :issue:`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 :issue:`40334`.)
Other Language Changes
__import__() now raises ImportError instead of ValueError, which used to occur when a relative import went past its top-level package. (Contributed by Ngalim Siregar in :issue:`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 by os.chdir(). As a side effect, the traceback also displays the absolute path for __main__ module frames in this case. (Contributed by Victor Stinner in :issue:`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() and bytes.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 :issue:`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 for bytes and bytearray objects. (Contributed by Serhiy Storchaka in :issue:`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 :issue:`39702`.)
Improved help for the typing module. Docstrings are now shown for all special forms and special generic aliases (like
Union
andList
). Using help() with generic alias likeList[int]
will show the help for the correspondent concrete type (list
in this case). (Contributed by Serhiy Storchaka in :issue:`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 :issue:`30773`.)Unexpected errors in calling the
__iter__
method are no longer masked byTypeError
in the in operator and functions contains(), indexOf() and countOf() of the operator module. (Contributed by Serhiy Storchaka in :issue:`40824`.)Unparenthesized lambda expressions can no longer be the expression part in an
if
clause in comprehensions and generator expressions. See :issue:`41848` and :issue:`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 :issue:`17005`.)
Improved Modules
ast
Added the indent option to dump() which allows it to produce a multiline indented output. (Contributed by Serhiy Storchaka in :issue:`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 :issue:`38870`.)
Added docstrings to AST nodes that contains the ASDL signature used to construct that node. (Contributed by Batuhan Taskaya in :issue:`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 :issue:`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 :issue:`34037`.)
Added asyncio.PidfdChildWatcher, a Linux-specific child watcher implementation that polls process file descriptors. (:issue:`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 :issue:`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 :issue:`32751`.)
asyncio now raises TyperError
when calling incompatible methods with an ssl.SSLSocket socket. (Contributed by Ido Michael in :issue:`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 :issue:`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 :issue:`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 :issue:`39349`.)
Removed daemon threads from ThreadPoolExecutor and ProcessPoolExecutor. This improves compatibility with subinterpreters and predictability in their shutdown processes. (Contributed by Kyle Stanley in :issue:`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 :issue:`39207`.)
curses
Added curses.get_escdelay(), curses.set_escdelay(), curses.get_tabsize(), and curses.set_tabsize() functions. (Contributed by Anthony Sottile in :issue:`38312`.)
datetime
The isocalendar() of datetime.date and isocalendar() of datetime.datetime methods now returns a namedtuple() instead of a tuple. (Contributed by Dong-hee Na in :issue:`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 :issue:`40698`.)
fcntl
Added constants F_OFD_GETLK
, F_OFD_SETLK
and F_OFD_SETLKW
. (Contributed by Dong-hee Na in :issue:`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 Dong-hee Na in :issue:`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 :issue:`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 :issue:`39322`.)
hashlib
The hashlib module can now use SHA3 hashes and SHAKE XOF from OpenSSL when available. (Contributed by Christian Heimes in :issue:`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 :issue:`40479`)
http
HTTP status codes 103 EARLY_HINTS
, 418 IM_A_TEAPOT
and 425 TOO_EARLY
are added to http.HTTPStatus. (Contributed by Dong-hee Na in :issue:`39509` and Ross Rhodes in :issue:`39507`.)
IDLE and idlelib
Added option to toggle cursor blink off. (Contributed by Zackery Spytz in :issue:`4603`.)
Escape key now closes IDLE completion windows. (Contributed by Johnny Najera in :issue:`38944`.)
Added keywords to module name completion list. (Contributed by Terry J. Reedy in :issue:`37765`.)
The changes above have been backported to 3.8 maintenance releases.
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 Dong-hee Na in :issue:`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 Dong-hee Na in :issue:`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 :issue:`37444`.)
Import loaders which publish immutable module objects can now publish immutable packages in addition to individual modules. (Contributed by Dino Viehland in :issue:`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 :issue:`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 :issue:`36350` and :issue:`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 :issue:`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 :issue:`36384`).
math
Expanded the math.gcd() function to handle multiple arguments. Formerly, it only supported two arguments. (Contributed by Serhiy Storchaka in :issue:`39648`.)
Added math.lcm(): return the least common multiple of specified arguments. (Contributed by Mark Dickinson, Ananthakrishnan and Serhiy Storchaka in :issue:`39479` and :issue:`39648`.)
Added math.nextafter(): return the next floating-point value after x towards y. (Contributed by Victor Stinner in :issue:`39288`.)
Added math.ulp(): return the value of the least significant bit of a float. (Contributed by Victor Stinner in :issue:`39310`.)
multiprocessing
The multiprocessing.SimpleQueue class has a new close() method to explicitly close the queue. (Contributed by Victor Stinner in :issue:`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 Dong-hee Na in :issue:`39259`.)
os
Added CLD_KILLED and CLD_STOPPED for si_code
. (Contributed by Dong-hee Na in :issue:`38493`.)
Exposed the Linux-specific os.pidfd_open() (:issue:`38692`) and os.P_PIDFD (:issue:`38713`) for process management with file descriptors.
The os.unsetenv() function is now also available on Windows. (Contributed by Victor Stinner in :issue:`39413`.)
The os.putenv() and os.unsetenv() functions are now always available. (Contributed by Victor Stinner in :issue:`39395`.)
Added os.waitstatus_to_exitcode() function: convert a wait status to an exit code. (Contributed by Victor Stinner in :issue:`40094`.)
pathlib
Added pathlib.Path.readlink() which acts similarly to os.readlink(). (Contributed by Girts Folkmanis in :issue:`30618`)
pdb
On Windows now Pdb supports ~/.pdbrc
. (Contributed by Tim Hopper and Dan Lidral-Porter in :issue:`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 Dong-hee Na in :issue:`39259`.)
pprint
pprint can now pretty-print types.SimpleNamespace. (Contributed by Carl Bordum Hansen in :issue:`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 :issue:`40257`.)
random
Added a new random.Random.randbytes
method: generate random bytes. (Contributed by Victor Stinner in :issue:`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. (:issue:`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 Dong-hee Na in :issue:`39259`.)
LMTP constructor now has an optional timeout parameter. (Contributed by Dong-hee Na in :issue:`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 :issue:`25780`.)
The socket module now supports the CAN_J1939 protocol on platforms that support it. (Contributed by Karl Ding in :issue:`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 :issue:`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 ms. (Contributed by Batuhan Taskaya in :issue:`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 :issue:`1294959`.)
Previously, sys.stderr was block-buffered when non-interactive. Now stderr
defaults to always being line-buffered. (Contributed by Jendrik Seipp in :issue:`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 :issue:`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.)
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 :issue:`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 :issue:`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 :issue:`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 :issue:`40010`.)
Optimized the subprocess module on FreeBSD using
closefrom()
. (Contributed by Ed Maste, Conrad Meyer, Kyle Evans, Kubilay Kocak and Victor Stinner in :issue:`38061`.)PyLong_FromDouble() is now up to 1.87x faster for values that fit into long. (Contributed by Sergey Fedoseev in :issue:`37986`.)
A number of Python builtins (range, tuple, set, frozenset, list, dict) are now sped up by using PEP 590 vectorcall protocol. (Contributed by Dong-hee Na, Mark Shannon, Jeroen Demeyer and Petr Viktorin in :issue:`37207`.)
Optimized
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 :issue:`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 :issue:`37257`.)floor division of float operation now has a better performance. Also the message of ZeroDivisionError for this operation is updated. (Contributed by Dong-hee Na in :issue:`39434`.)
Decoding short ASCII strings with UTF-8 and ascii codecs is now about 15% faster. (Contributed by Inada Naoki in :issue:`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 :issue:`39586`.)Currently math.factorial() accepts float instances with non-negative integer values (like
5.0
). It raises a ValueError for non-integral and negative floats. It is now deprecated. In future Python versions it will raise a TypeError for all floats. (Contributed by Serhiy Storchaka in :issue:`37315`.)The parser and symbol 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 the ast module.
The Public C API functions PyParser_SimpleParseStringFlags(), PyParser_SimpleParseStringFlagsFilename(), PyParser_SimpleParseFileFlags() and
PyNode_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 a TypeError in a future version of Python. (Contributed by Josh Rosenberg in :issue:`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 to None, int, float, str, bytes, and bytearray.
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 :issue:`28286`.)
Deprecated the
split()
method of_tkinter.TkappType
in favour of thesplitlist()
method which has more consistent and predicable behavior. (Contributed by Serhiy Storchaka in :issue:`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 :issue:`34790`.)binhex4 and hexbin4 standards are now deprecated. The binhex module and the following binascii functions are now deprecated:
(Contributed by Victor Stinner in :issue:`39353`.)
ast classes
slice
,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 :issue:`34822`.)ast classes
Suite
,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 :issue:`39639` and :issue:`39969` and Serhiy Storchaka in :issue:`39988`.)The PyEval_InitThreads() and PyEval_ThreadsInitialized() functions are now deprecated and will be removed in Python 3.11. Calling PyEval_InitThreads() now does nothing. The GIL is initialized by Py_Initialize() since Python 3.7. (Contributed by Victor Stinner in :issue:`39877`.)
Passing
None
as the first argument to the shlex.split() function has been deprecated. (Contributed by Zackery Spytz in :issue:`33262`.)smtpd.MailmanProxy() is now deprecated as it is unusable without an external module,
mailman
. (Contributed by Samuel Colvin in :issue:`35800`.)The lib2to3 module now emits a PendingDeprecationWarning. 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. The
lib2to3
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 :issue:`40360`.)The random parameter of random.shuffle() has been deprecated. (Contributed by Raymond Hettinger in :issue:`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 use nntplib.NNTP.descriptions() or nntplib.NNTP.description() instead. (Contributed by Dong-hee Na in :issue:`39366`.) - array.array:
tostring()
andfromstring()
methods have been removed. They were aliases totobytes()
andfrombytes()
, deprecated since Python 3.2. (Contributed by Victor Stinner in :issue:`38916`.) - The undocumented
sys.callstats()
function has been removed. Since Python 3.7, it was deprecated and always returned None. It required a special build optionCALL_PROFILE
which was already removed in Python 3.7. (Contributed by Victor Stinner in :issue:`37414`.) - The
sys.getcheckinterval()
andsys.setcheckinterval()
functions have been removed. They were deprecated since Python 3.2. Use sys.getswitchinterval() and sys.setswitchinterval() instead. (Contributed by Victor Stinner in :issue:`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 :issue:`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 :issue:`37312`.)aifc.openfp()
alias toaifc.open()
,sunau.openfp()
alias tosunau.open()
, andwave.openfp()
alias to wave.open() have been removed. They were deprecated since Python 3.7. (Contributed by Victor Stinner in :issue:`37320`.)- The
isAlive()
method of threading.Thread has been removed. It was deprecated since Python 3.8. Use is_alive() instead. (Contributed by Dong-hee Na in :issue:`37804`.) - Methods
getchildren()
andgetiterator()
of classes ElementTree and Element in the ElementTree 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 :issue:`36543`.) - The old plistlib API has been removed, it was deprecated since Python 3.4. Use the load(), loads(), dump(), and dumps() functions. Additionally, the use_builtin_types parameter was removed, standard bytes objects are always used instead. (Contributed by Jon Janzen in :issue:`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 :issue:`15088`) base64.encodestring()
andbase64.decodestring()
, aliases deprecated since Python 3.1, have been removed: use base64.encodebytes() and base64.decodebytes() instead. (Contributed by Victor Stinner in :issue:`39351`.)fractions.gcd()
function has been removed, it was deprecated since Python 3.5 (:issue:`22486`): use math.gcd() instead. (Contributed by Victor Stinner in :issue:`39350`.)- The buffering parameter of bz2.BZ2File has been removed. Since Python 3.0, it was ignored and using it emitted a DeprecationWarning. Pass an open file object to control how the file is opened. (Contributed by Victor Stinner in :issue:`39357`.)
- The encoding parameter of json.loads() has been removed. As of Python 3.1, it was deprecated and ignored; using it has emitted a DeprecationWarning since Python 3.8. (Contributed by Inada Naoki in :issue:`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 :issue:`34793`.)- The
sys.getcounts()
function, the-X showalloccount
command line option and theshow_alloc_count
field of the C structure PyConfig have been removed. They required a special Python build by definingCOUNT_ALLOCS
macro. (Contributed by Victor Stinner in :issue:`39489`.) - The
_field_types
attribute of the typing.NamedTuple class has been removed. It was deprecated since Python 3.8. Use the__annotations__
attribute instead. (Contributed by Serhiy Storchaka in :issue:`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 :issue:`40208`) - The
asyncio.Task.current_task()
andasyncio.Task.all_tasks()
have been removed. They were deprecated since Python 3.7 and you can use asyncio.current_task() and asyncio.all_tasks() instead. (Contributed by Rémi Lapeyre in :issue:`40967`) - The
unescape()
method in the html.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__() and importlib.util.resolve_name() now raise ImportError where it previously raised ValueError. Callers catching the specific exception type and supporting both Python 3.9 and earlier versions will need to catch both using
except (ImportError, ValueError):
. - The venv activation scripts no longer special-case when
__VENV_PROMPT__
is set to""
. - The select.epoll.unregister() method no longer ignores the EBADF error. (Contributed by Victor Stinner in :issue:`39239`.)
- The compresslevel parameter of bz2.BZ2File became keyword-only, since the buffering parameter has been removed. (Contributed by Victor Stinner in :issue:`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 :issue:`34822`.) - The importlib module now ignores the PYTHONCASEOK environment variable when the -E or -I command line options are being used.
- The encoding parameter has been added to the classes ftplib.FTP and ftplib.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 to AbstractEventLoop, meaning alternative event loops that inherit from it should have this method defined. (Contributed by Kyle Stanley in :issue:`34037`.)- The constant values of future flags in the __future__ module is updated in order to prevent collision with compiler flags. Previously
PyCF_ALLOW_TOP_LEVEL_AWAIT
was clashing withCO_FUTURE_DIVISION
. (Contributed by Batuhan Taskaya in :issue:`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 :issue:`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 :issue:`37742`.) - Division handling of PurePath now returns
NotImplemented
instead of raising a TypeError when passed something other than an instance ofstr
or PurePath. This allows creating compatible classes that don’t inherit from those mentioned types. (Contributed by Roger Aiudi in :issue:`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 function socket.inet_aton() treats leading zeros as octal notatation. glibc implementation of modern inet_pton() does not accept any leading zeros. (Contributed by Christian Heimes in :issue:`36384`).
- codecs.lookup() now normalizes the encoding name the same way as
encodings.normalize_encoding()
, except that codecs.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 :issue:`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 custom tp_traverse function, ensure that all custom
tp_traverse
functions of heap-allocated types visit the object’s type.Example:
int foo_traverse(foo_struct *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 types 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 (Python issue 35810 and 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
(See :issue:`35810` and :issue:`40217` for more information.)
The functions
PyEval_CallObject
,PyEval_CallFunction
,PyEval_CallMethod
andPyEval_CallObjectWithKeywords
are deprecated. Use PyObject_Call() and its variants instead. (See more details in :issue:`29548`.)
CPython bytecode changes
The :opcode:`LOAD_ASSERTION_ERROR` opcode was added for handling the assert statement. Previously, the assert statement would not work correctly if the AssertionError exception was being shadowed. (Contributed by Zackery Spytz in :issue:`34880`.)
The :opcode:`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 :issue:`39156`.)
Build Changes
- Added
--with-platlibdir
option to theconfigure
script: name of the platform-specific library directory, stored in the new sys.platlibdir attribute. See sys.platlibdir attribute for more information. (Contributed by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner in :issue:`1294959`.) - The
COUNT_ALLOCS
special build macro has been removed. (Contributed by Victor Stinner in :issue:`39489`.) - On non-Windows platforms, the
setenv()
andunsetenv()
functions are now required to build Python. (Contributed by Victor Stinner in :issue:`39395`.) - On non-Windows platforms, creating
bdist_wininst
installers is now officially unsupported. (See :issue:`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 :issue:`34956`.) - Python can now be built for Windows 10 ARM64. (Contributed by Steve Dower in :issue:`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 :issue:`36044` and :issue:`37707` for more details.)
C API Changes
New Features
PEP 573: Added PyType_FromModuleAndSpec() to associate a module with a class; PyType_GetModule() and PyType_GetModuleState() to retrieve the module and its state; and PyCMethod and
METH_METHOD
to allow a method to access the class it was defined in. (Contributed by Marcel Plch and Petr Viktorin in :issue:`38787`.)Added PyFrame_GetCode() function: get a frame code. Added PyFrame_GetBack() function: get the frame next outer frame. (Contributed by Victor Stinner in :issue:`40421`.)
Added PyFrame_GetLineNumber() to the limited C API. (Contributed by Victor Stinner in :issue:`40421`.)
Added PyThreadState_GetInterpreter() and PyInterpreterState_Get() functions to get the interpreter. Added PyThreadState_GetFrame() function to get the current frame of a Python thread state. Added PyThreadState_GetID() function: get the unique identifier of a Python thread state. (Contributed by Victor Stinner in :issue:`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 :issue:`37194`.)
Changes in the limited C API (if
Py_LIMITED_API
macro is defined):Provide Py_EnterRecursiveCall() and Py_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 access
PyThreadState.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.
(Contributed by Victor Stinner in :issue:`38644` and :issue:`39542`.)
The PyModule_AddType() function is added to help adding a type to a module. (Contributed by Dong-hee Na in :issue:`40024`.)
Added the functions PyObject_GC_IsTracked() and PyObject_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 :issue:`40241`.)
Added
_PyObject_FunctionStr()
to get a user-friendly string representation of a function-like object. (Patch by Jeroen Demeyer in :issue:`37645`.)Added PyObject_CallOneArg() for calling an object with one positional argument (Patch by Jeroen Demeyer in :issue:`37483`.)
Porting to Python 3.9
PyInterpreterState.eval_frame
(PEP 523) now requires a new mandatory tstate parameter (PyThreadState*
). (Contributed by Victor Stinner in :issue:`38500`.)Extension modules: m_traverse, m_clear and m_free functions of PyModuleDef 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 if m_size is greater than 0 and the module state (as returned by PyModule_GetState()) is
NULL
.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 :issue:`39984`.)
The Windows registry is no longer used to initialize sys.path when the
-E
option is used (if PyConfig.use_environment is set to0
). This is significant when embedding Python on Windows. (Contributed by Zackery Spytz in :issue:`8901`.)The global variable PyStructSequence_UnnamedField is now a constant and refers to a constant string. (Contributed by Serhiy Storchaka in :issue:`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 :issue:`40241`.)The
Py_UNICODE_COPY
,Py_UNICODE_FILL
,PyUnicode_WSTR_LENGTH
, PyUnicode_FromUnicode(), PyUnicode_AsUnicode(),_PyUnicode_AsUnicode
, and PyUnicode_AsUnicodeAndSize() are marked as deprecated in C. They have been deprecated by PEP 393 since Python 3.3. (Contributed by Inada Naoki in :issue:`36346`.)The Py_FatalError() function is replaced with a macro which logs automatically the name of the current function, unless the
Py_LIMITED_API
macro is defined. (Contributed by Victor Stinner in :issue:`39882`.)The vectorcall protocol now requires that the caller passes only strings as keyword names. (See :issue:`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 the PyObject_New() macro, and thePyObject_NEW_VAR()
macro becomes an alias to the PyObject_NewVar() macro. They no longer access directly the PyTypeObject.tp_basicsize member.PyObject_GET_WEAKREFS_LISTPTR()
macro was converted to a function: the macro accessed directly the PyTypeObject.tp_weaklistoffset member.PyObject_CheckBuffer() macro was converted to a function: the macro accessed directly the PyTypeObject.tp_as_buffer member.
PyIndex_Check() is now always declared as an opaque function to hide implementation details: removed the
PyIndex_Check()
macro. The macro accessed directly the PyTypeObject.tp_as_number member.
(See :issue:`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 :issue:`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 :issue:`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 :issue:`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)
(Contributed by Victor Stinner in :issue:`38644` and :issue:`39542`.)
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 :issue:`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 :issue:`37340`, :issue:`38896` and :issue:`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 :issue:`39465`.)Removed
Py_UNICODE_MATCH
. It has been deprecated by PEP 393, and broken since Python 3.3. The PyUnicode_Tailmatch() function can be used instead. (Contributed by Inada Naoki in :issue:`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 :issue:`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 a TypeError 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 :issue:`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 :issue:`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 :issue:`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 :issue:`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 :issue:`43285`)
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 :issue:`43882`)