PEP 649 &PEP 749: Deferred evaluation of annotations¶

Theannotations on functions, classes, and modules are nolonger evaluated eagerly. Instead, annotations are stored in special-purposeannotate functions and evaluated only whennecessary (except iffrom__future__importannotations is used).

This change is designed to improve performance and usability of annotationsin Python in most circumstances. The runtime cost for defining annotations isminimized, but it remains possible to introspect annotations at runtime.It is no longer necessary to enclose annotations in strings if theycontain forward references.

The newannotationlib module provides tools for inspecting deferredannotations. Annotations may be evaluated in theVALUEformat (which evaluates annotations to runtime values, similar to the behavior inearlier Python versions), theFORWARDREF format(which replaces undefined names with special markers), and theSTRING format (which returns annotations as strings).

This example shows how these formats behave:

>>>fromannotationlibimportget_annotations,Format>>>deffunc(arg:Undefined):...pass>>>get_annotations(func,format=Format.VALUE)Traceback (most recent call last):...NameError:name 'Undefined' is not defined>>>get_annotations(func,format=Format.FORWARDREF){'arg': ForwardRef('Undefined', owner=<function func at 0x...>)}>>>get_annotations(func,format=Format.STRING){'arg': 'Undefined'}

Theporting section contains guidanceon changes that may be needed due to these changes, though in the majority ofcases, code will continue working as-is.

(Contributed by Jelle Zijlstra inPEP 749 andgh-119180;PEP 649 was written by Larry Hastings.)

PEP 734: Multiple interpreters in the standard library¶

The CPython runtime supports running multiple copies of Python in thesame process simultaneously and has done so for over 20 years.Each of these separate copies is called an ‘interpreter’.However, the feature had been available only throughtheC-API.

That limitation is removed in Python 3.14,with the newconcurrent.interpreters module.

There are at least two notable reasons why using multiple interpretershas significant benefits:

• they support a new (to Python), human-friendly concurrency model

• true multi-core parallelism

For some use cases, concurrency in software improves efficiency andcan simplify design, at a high level.At the same time, implementing and maintaining all but the simplest concurrencyis often a struggle for the human brain.That especially applies to plain threads (for example,threading),where all memory is shared between all threads.

With multiple isolated interpreters, you can take advantage of a classof concurrency models, like Communicating Sequential Processes (CSP)or the actor model, that have foundsuccess in other programming languages, like Smalltalk, Erlang,Haskell, and Go. Think of multiple interpreters as threadsbut with opt-in sharing.

Regarding multi-core parallelism: as of Python 3.12, interpretersare now sufficiently isolated from one another to be used in parallel(seePEP 684). This unlocks a variety of CPU-intensive use casesfor Python that were limited by theGIL.

Using multiple interpreters is similar in many ways tomultiprocessing, in that they both provide isolated logical“processes” that can run in parallel, with no sharing by default.However, when using multiple interpreters, an application will usefewer system resources and will operate more efficiently (since itstays within the same process). Think of multiple interpreters ashaving the isolation of processes with the efficiency of threads.

While the feature has been around for decades, multiple interpretershave not been used widely, due to low awareness and the lack of astandard library module. Consequently, they currently have severalnotable limitations, which are expected to improve significantly nowthat the feature is going mainstream.

Current limitations:

• starting each interpreter has not been optimized yet

• each interpreter uses more memory than necessary(work continues on extensive internal sharing between interpreters)

• there aren’t many optionsyet for truly sharing objects or otherdata between interpreters (other thanmemoryview)

• many third-party extension modules on PyPI are not yet compatiblewith multiple interpreters(all standard library extension modulesare compatible)

• the approach to writing applications that use multiple isolatedinterpreters is mostly unfamiliar to Python users, for now

The impact of these limitations will depend on future CPythonimprovements, how interpreters are used, and what the community solvesthrough PyPI packages. Depending on the use case, the limitations maynot have much impact, so try it out!

Furthermore, future CPython releases will reduce or eliminate overheadand provide utilities that are less appropriate on PyPI. In themeantime, most of the limitations can also be addressed throughextension modules, meaning PyPI packages can fill any gap for 3.14, andeven back to 3.12 where interpreters were finally properly isolated andstopped sharing theGIL. Likewise, libraries on PyPI are expectedto emerge for high-level abstractions on top of interpreters.

Regarding extension modules, work is in progress to update some PyPIprojects, as well as tools like Cython, pybind11, nanobind, and PyO3.The steps for isolating an extension module are found atIsolating Extension Modules.Isolating a module has a lot of overlap with what is required to supportfree-threading, so the ongoingwork in the community in that area will help accelerate supportfor multiple interpreters.

Also added in 3.14:concurrent.futures.InterpreterPoolExecutor.

(Contributed by Eric Snow ingh-134939.)

PEP 750: Template string literals¶

Template strings are a new mechanism for custom string processing.They share the familiar syntax of f-strings but, unlike f-strings,return an object representing the static and interpolated parts ofthe string, instead of a simplestr.

To write a t-string, use a't' prefix instead of an'f':

>>>variety='Stilton'>>>template=t'Try some{variety} cheese!'>>>type(template)<class 'string.templatelib.Template'>

Template objects provide access to the staticand interpolated (in curly braces) parts of a stringbefore they are combined.Iterate overTemplate instances to access their parts in order:

>>>list(template)['Try some ', Interpolation('Stilton', 'variety', None, ''), ' cheese!']

It’s easy to write (or call) code to processTemplate instances.For example, here’s a function that renders static parts lowercase andInterpolation instances uppercase:

fromstring.templatelibimportInterpolationdeflower_upper(template):"""Render static parts lowercase and interpolations uppercase."""parts=[]forpartintemplate:ifisinstance(part,Interpolation):parts.append(str(part.value).upper())else:parts.append(part.lower())return''.join(parts)name='Wenslydale'template=t'Mister{name}'assertlower_upper(template)=='mister WENSLYDALE'

BecauseTemplate instances distinguish between static strings andinterpolations at runtime, they can be useful for sanitising user input.Writing ahtml() function that escapes user input in HTML is an exerciseleft to the reader!Template processing code can provide improved flexibility.For instance, a more advancedhtml() function could acceptadict of HTML attributes directly in the template:

attributes={'src':'limburger.jpg','alt':'lovely cheese'}template=t'<img{attributes}>'asserthtml(template)=='<img src="limburger.jpg" alt="lovely cheese" />'

Of course, template processing code does not need to return a string-like result.An evenmore advancedhtml() could return a custom type representinga DOM-like structure.

With t-strings in place, developers can write systems that sanitise SQL,make safe shell operations, improve logging, tackle modern ideas in webdevelopment (HTML, CSS, and so on), and implement lightweight custom business DSLs.

(Contributed by Jim Baker, Guido van Rossum, Paul Everitt, Koudai Aono,Lysandros Nikolaou, Dave Peck, Adam Turner, Jelle Zijlstra, Bénédikt Tran,and Pablo Galindo Salgado ingh-132661.)

PEP 768: Safe external debugger interface¶

Python 3.14 introduces a zero-overhead debugging interface that allowsdebuggers and profilers to safely attach to running Python processeswithout stopping or restarting them.This is a significant enhancement to Python’s debugging capabilities,meaning that unsafe alternatives are no longer required.

The new interface provides safe execution points for attaching debugger codewithout modifying the interpreter’s normal execution pathor adding any overhead at runtime.Due to this, tools can now inspect and interact with Python applicationsin real-time, which is a crucial capability for high-availability systemsand production environments.

For convenience, this interface is implemented in thesys.remote_exec()function. For example:

importsysfromtempfileimportNamedTemporaryFilewithNamedTemporaryFile(mode='w',suffix='.py',delete=False)asf:script_path=f.namef.write(f'import my_debugger; my_debugger.connect({os.getpid()})')# Execute in process with PID 1234print('Behold! An offering:')sys.remote_exec(1234,script_path)

This function allows sending Python code to be executed in a target processat the next safe execution point.However, tool authors can also implement the protocol directly as describedin the PEP, which details the underlying mechanisms used to safely attach torunning processes.

The debugging interface has been carefully designed with security in mindand includes several mechanisms to control access:

• APYTHON_DISABLE_REMOTE_DEBUG environment variable.

• A-Xdisable-remote-debug command-line option.

• A--without-remote-debug configure flag to completely disablethe feature at build time.

(Contributed by Pablo Galindo Salgado, Matt Wozniski, and Ivona Stojanovicingh-131591.)

A new type of interpreter¶

A new type of interpreter has been added to CPython.It uses tail calls between small C functions that implement individualPython opcodes, rather than one large Ccase statement.For certain newer compilers, this interpreter providessignificantly better performance. Preliminary benchmarks suggest a geometricmean of 3-5% faster on the standardpyperformance benchmark suite,depending on platform and architecture.The baseline is Python 3.14 built with Clang 19, without this new interpreter.

This interpreter currently only works with Clang 19 and neweron x86-64 and AArch64 architectures.However, a future release of GCC is expected to support this as well.

This feature is opt-in for now. Enabling profile-guided optimization is highlyrecommendeded when using the new interpreter as it is the only configurationthat has been tested and validated for improved performance.For further information, see--with-tail-call-interp.

(Contributed by Ken Jin ingh-128563, with ideas on how to implement thisin CPython by Mark Shannon, Garrett Gu, Haoran Xu, and Josh Haberman.)

Free-threaded mode improvements¶

CPython’s free-threaded mode (PEP 703), initially added in 3.13,has been significantly improved in Python 3.14.The implementation described in PEP 703 has been finished, including C APIchanges, and temporary workarounds in the interpreter were replaced withmore permanent solutions.The specializing adaptive interpreter (PEP 659) is now enabledin free-threaded mode, which along with many other optimizationsgreatly improves its performance.The performance penalty on single-threaded code in free-threaded modeis now roughly 5-10%, depending on the platform and C compiler used.

From Python 3.14, when compiling extension modules for the free-threaded build ofCPython on Windows, the preprocessor variablePy_GIL_DISABLED now needs tobe specified by the build backend, as it will no longer be determinedautomatically by the C compiler. For a running interpreter, the setting thatwas used at compile time can be found usingsysconfig.get_config_var().

The new-Xcontext_aware_warnings flag controls ifconcurrent safe warnings controlis enabled. The flag defaults to true for the free-threaded buildand false for the GIL-enabled build.

A newthread_inherit_context flag has been added,which if enabled means that threads created withthreading.Threadstart with a copy of theContext() of the caller ofstart(). Most significantly, this makes the warningfiltering context established bycatch_warnings be“inherited” by threads (or asyncio tasks) started within that context. It alsoaffects other modules that use context variables, such as thedecimalcontext manager.This flag defaults to true for the free-threaded build and false forthe GIL-enabled build.

(Contributed by Sam Gross, Matt Page, Neil Schemenauer, Thomas Wouters,Donghee Na, Kirill Podoprigora, Ken Jin, Itamar Oren, Brett Simmers,Dino Viehland, Nathan Goldbaum, Ralf Gommers, Lysandros Nikolaou, Kumar Aditya,Edgar Margffoy, and many others.Some of these contributors are employed by Meta, which has continued to providesignificant engineering resources to support this project.)

Improved error messages¶

• The interpreter now provides helpful suggestions when it detects typos in Pythonkeywords. When a word that closely resembles a Python keyword is encountered,the interpreter will suggest the correct keyword in the error message. Thisfeature helps programmers quickly identify and fix common typing mistakes. Forexample:

  >>>whilleTrue:...passTraceback (most recent call last):  File"<stdin>", line1whilleTrue:^^^^^^SyntaxError:invalid syntax. Did you mean 'while'?

  While the feature focuses on the most common cases, some variations ofmisspellings may still result in regular syntax errors.(Contributed by Pablo Galindo ingh-132449.)

• elif statements that follow anelse block now havea specific error message.(Contributed by Steele Farnsworth ingh-129902.)

  >>>ifwho=="me":...print("It's me!")...else:...print("It's not me!")...elifwhoisNone:...print("Who is it?")File "<stdin>", line 5  elif who is None:  ^^^^SyntaxError: 'elif' block follows an 'else' block

• If a statement is passed to theConditional expressions afterelse,or one ofpass,break, orcontinueis passed beforeif, then theerror message highlights where theexpression isrequired. (Contributed by Sergey Miryanov ingh-129515.)

  >>>x=1ifTrueelsepassTraceback (most recent call last):  File"<string>", line1x=1ifTrueelsepass^^^^SyntaxError:expected expression after 'else', but statement is given>>>x=continueifTrueelsebreakTraceback (most recent call last):  File"<string>", line1x=continueifTrueelsebreak^^^^^^^^SyntaxError:expected expression before 'if', but statement is given

• When incorrectly closed strings are detected, the error message suggeststhat the string may be intended to be part of the string.(Contributed by Pablo Galindo ingh-88535.)

  >>>"The interesting object "Theimportantobject" is very important"Traceback (most recent call last):SyntaxError:invalid syntax. Is this intended to be part of the string?

• When strings have incompatible prefixes, the error now showswhich prefixes are incompatible.(Contributed by Nikita Sobolev ingh-133197.)

  >>>ub'abc'  File"<python-input-0>", line1ub'abc'^^SyntaxError:'u' and 'b' prefixes are incompatible

• Improved error messages when usingas with incompatible targets in:

  • Imports:import...as...

  • From imports:from...import...as...

  • Except handlers:except...as...

  • Pattern-match cases:case...as...

  (Contributed by Nikita Sobolev ingh-123539,gh-123562, andgh-123440.)

• Improved error message when trying to add an instance of an unhashable type toadict orset.(Contributed by CF Bolz-Tereick and Victor Stinner ingh-132828.)

  >>>s=set()>>>s.add({'pages':12,'grade':'A'})Traceback (most recent call last):  File"<python-input-1>", line1, in<module>s.add({'pages':12,'grade':'A'})~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^TypeError:cannot use 'dict' as a set element (unhashable type: 'dict')>>>d={}>>>l=[1,2,3]>>>d[l]=12Traceback (most recent call last):  File"<python-input-4>", line1, in<module>d[l]=12~^^^TypeError:cannot use 'list' as a dict key (unhashable type: 'list')

• Improved error message when an object supporting the synchronouscontext manager protocol is entered usingasyncwithinstead ofwith,and vice versa for the asynchronous context manager protocol.(Contributed by Bénédikt Tran ingh-128398.)

PEP 784: Zstandard support in the standard library¶

The newcompression package contains modulescompression.lzma,compression.bz2,compression.gzip andcompression.zlibwhich re-export thelzma,bz2,gzip andzlibmodules respectively. The new import names undercompression are thepreferred names for importing these compression modules from Python 3.14. However,the existing modules names have not been deprecated. Any deprecation or removalof the existing compression modules will occur no sooner than five years afterthe release of 3.14.

The newcompression.zstd module provides compression and decompressionAPIs for the Zstandard format via bindings toMeta’s zstd library. Zstandard is a widely adopted, highlyefficient, and fast compression format. In addition to the APIs introduced incompression.zstd, support for reading and writing Zstandard compressedarchives has been added to thetarfile,zipfile, andshutil modules.

Here’s an example of using the new module to compress some data:

fromcompressionimportzstdimportmathdata=str(math.pi).encode()*20compressed=zstd.compress(data)ratio=len(compressed)/len(data)print(f"Achieved compression ratio of{ratio}")

As can be seen, the API is similar to the APIs of thelzma andbz2 modules.

(Contributed by Emma Harper Smith, Adam Turner, Gregory P. Smith, Tomas Roun,Victor Stinner, and Rogdham ingh-132983.)

Asyncio introspection capabilities¶

Added a new command-line interface to inspect running Python processesusing asynchronous tasks, available viapython-masynciopsPIDorpython-masynciopstreePID.

Theps subcommand inspects the given process ID (PID) and displaysinformation about currently running asyncio tasks.It outputs a task table: a flat listing of all tasks, their names,their coroutine stacks, and which tasks are awaiting them.

Thepstree subcommand fetches the same information, but instead renders avisual async call tree, showing coroutine relationships in a hierarchical format.This command is particularly useful for debugging long-running or stuckasynchronous programs.It can help developers quickly identify where a program is blocked,what tasks are pending, and how coroutines are chained together.

For example given this code:

importasyncioasyncdefplay_track(track):awaitasyncio.sleep(5)print(f'🎵 Finished:{track}')asyncdefplay_album(name,tracks):asyncwithasyncio.TaskGroup()astg:fortrackintracks:tg.create_task(play_track(track),name=track)asyncdefmain():asyncwithasyncio.TaskGroup()astg:tg.create_task(play_album('Sundowning',['TNDNBTG','Levitate']),name='Sundowning')tg.create_task(play_album('TMBTE',['DYWTYLM','Aqua Regia']),name='TMBTE')if__name__=='__main__':asyncio.run(main())

Executing the new tool on the running process will yield a table like this:

python-masynciops12345tidtaskidtasknamecoroutinestackawaiterchainawaiternameawaiterid------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------19355000x7fc930c18050Task-1TaskGroup._aexit->TaskGroup.__aexit__->main0x019355000x7fc930c18230SundowningTaskGroup._aexit->TaskGroup.__aexit__->albumTaskGroup._aexit->TaskGroup.__aexit__->mainTask-10x7fc930c1805019355000x7fc93173fa50TMBTETaskGroup._aexit->TaskGroup.__aexit__->albumTaskGroup._aexit->TaskGroup.__aexit__->mainTask-10x7fc930c1805019355000x7fc93173fdf0TNDNBTGsleep->playTaskGroup._aexit->TaskGroup.__aexit__->albumSundowning0x7fc930c1823019355000x7fc930d32510Levitatesleep->playTaskGroup._aexit->TaskGroup.__aexit__->albumSundowning0x7fc930c1823019355000x7fc930d32890DYWTYLMsleep->playTaskGroup._aexit->TaskGroup.__aexit__->albumTMBTE0x7fc93173fa5019355000x7fc93161ec30AquaRegiasleep->playTaskGroup._aexit->TaskGroup.__aexit__->albumTMBTE0x7fc93173fa50

or a tree like this:

python-masynciopstree12345└──(T)Task-1└──mainexample.py:13└──TaskGroup.__aexit__Lib/asyncio/taskgroups.py:72└──TaskGroup._aexitLib/asyncio/taskgroups.py:121├──(T)Sundowning│└──albumexample.py:8│└──TaskGroup.__aexit__Lib/asyncio/taskgroups.py:72│└──TaskGroup._aexitLib/asyncio/taskgroups.py:121│├──(T)TNDNBTG││└──playexample.py:4││└──sleepLib/asyncio/tasks.py:702│└──(T)Levitate│└──playexample.py:4│└──sleepLib/asyncio/tasks.py:702└──(T)TMBTE└──albumexample.py:8└──TaskGroup.__aexit__Lib/asyncio/taskgroups.py:72└──TaskGroup._aexitLib/asyncio/taskgroups.py:121├──(T)DYWTYLM│└──playexample.py:4│└──sleepLib/asyncio/tasks.py:702└──(T)AquaRegia└──playexample.py:4└──sleepLib/asyncio/tasks.py:702

If a cycle is detected in the async await graph (which could indicate aprogramming issue), the tool raises an error and lists the cycle paths thatprevent tree construction:

python-masynciopstree12345ERROR:await-graphcontainscycles-cannotprintatree!cycle:Task-2→Task-3→Task-2

(Contributed by Pablo Galindo, Łukasz Langa, Yury Selivanov, and MartaGomez Macias ingh-91048.)

Concurrent safe warnings control¶

Thewarnings.catch_warnings context manager will now optionallyuse a context variable for warning filters. This is enabled by settingthecontext_aware_warnings flag, either with the-Xcommand-line option or an environment variable. This gives predictablewarnings control when usingcatch_warnings combined withmultiple threads or asynchronous tasks. The flag defaults to true for thefree-threaded build and false for the GIL-enabled build.

(Contributed by Neil Schemenauer and Kumar Aditya ingh-130010.)

Built-ins¶

• Thebytes.fromhex() andbytearray.fromhex() methods now acceptASCIIbytes andbytes-like objects.(Contributed by Daniel Pope ingh-129349.)

• Add class methodsfloat.from_number() andcomplex.from_number()to convert a number tofloat orcomplex type correspondingly.They raise aTypeError if the argument is not a real number.(Contributed by Serhiy Storchaka ingh-84978.)

• Support underscore and comma as thousands separators in the fractional partfor floating-point presentation types of the new-style string formatting(withformat() orf-strings).(Contributed by Sergey B Kirpichev ingh-87790.)

• Theint() function no longer delegates to__trunc__().Classes that want to support conversion toint() must implementeither__int__() or__index__().(Contributed by Mark Dickinson ingh-119743.)

• Themap() function now has an optional keyword-onlystrict flaglikezip() to check that all the iterables are of equal length.(Contributed by Wannes Boeykens ingh-119793.)

• Thememoryview type now supports subscription,making it ageneric type.(Contributed by Brian Schubert ingh-126012.)

• UsingNotImplemented in a boolean contextwill now raise aTypeError.This has raised aDeprecationWarning since Python 3.9.(Contributed by Jelle Zijlstra ingh-118767.)

• Three-argumentpow() now tries calling__rpow__()if necessary.Previously it was only called in two-argumentpow()and the binary power operator.(Contributed by Serhiy Storchaka ingh-130104.)

• super objects are nowcopyable andpickleable.(Contributed by Serhiy Storchaka ingh-125767.)

Command line and environment¶

• The import time flag can now track modules that are already loaded (‘cached’),via the new-Ximporttime=2.When such a module is imported, theself andcumulative timesare replaced by the stringcached.

  Values above2 for-Ximporttime are now reserved for future use.

  (Contributed by Noah Kim and Adam Turner ingh-118655.)

• The command-line option-c now automatically dedents its codeargument before execution. The auto-dedentation behavior mirrorstextwrap.dedent().(Contributed by Jon Crall and Steven Sun ingh-103998.)

• -J is no longer a reserved flag forJython,and now has no special meaning.(Contributed by Adam Turner ingh-133336.)

PEP 758: Allowexcept andexcept* expressions without brackets¶

Theexcept andexcept* expressionsnow allow brackets to be omitted when there are multiple exception typesand theas clause is not used.For example:

try:connect_to_server()exceptTimeoutError,ConnectionRefusedError:print('The network has ceased to be!')

(Contributed by Pablo Galindo and Brett Cannon inPEP 758 andgh-131831.)

PEP 765: Control flow infinally blocks¶

The compiler now emits aSyntaxWarning when areturn,break, orcontinue statement have the effect ofleaving afinally block.This change is specified inPEP 765.

In situations where this change is inconvenient (such as those where thewarnings are redundant due to code linting), thewarning filter can be used to turn off all syntax warnings by addingignore::SyntaxWarning as a filter. This can be specified in combinationwith a filter that converts other warnings to errors (for example, passing-Werror-Wignore::SyntaxWarning as CLI options, or settingPYTHONWARNINGS=error,ignore::SyntaxWarning).

Note that applying such a filter at runtime using thewarnings modulewill only suppress the warning in code that is compiledafter the filter isadjusted. Code that is compiled prior to the filter adjustment (for example,when a module is imported) will still emit the syntax warning.

(Contributed by Irit Katriel ingh-130080.)

Incremental garbage collection¶

The cycle garbage collector is now incremental.This means that maximum pause times are reducedby an order of magnitude or more for larger heaps.

There are now only two generations: young and old.Whengc.collect() is not called directly, theGC is invoked a little less frequently. When invoked, itcollects the young generation and an increment of theold generation, instead of collecting one or more generations.

The behavior ofgc.collect() changes slightly:

• gc.collect(1): Performs an increment of garbage collection,rather than collecting generation 1.

• Other calls togc.collect() are unchanged.

(Contributed by Mark Shannon ingh-108362.)

Default interactive shell¶

• The defaultinteractive shell now highlights Python syntax.The feature is enabled by default, save ifPYTHON_BASIC_REPLor any other environment variable that disables colour is set.SeeControlling color for details.

  The default color theme for syntax highlighting strives for good contrastand exclusively uses the 4-bit VGA standard ANSI color codes for maximumcompatibility. The theme can be customized using an experimental API_colorize.set_theme().This can be called interactively or in thePYTHONSTARTUP script.Note that this function has no stability guarantees,and may change or be removed.

  (Contributed by Łukasz Langa ingh-131507.)

• The defaultinteractive shell now supports import auto-completion.This means that typingimportco and pressing<Tab> will suggestmodules starting withco. Similarly, typingfromconcurrentimportiwill suggest submodules ofconcurrent starting withi.Note that autocompletion of module attributes is not currently supported.(Contributed by Tomas Roun ingh-69605.)

argparse¶

• The default value of theprogram name forargparse.ArgumentParser now reflects the way the Pythoninterpreter was instructed to find the__main__ module code.(Contributed by Serhiy Storchaka and Alyssa Coghlan ingh-66436.)

• Introduced the optionalsuggest_on_error parameter toargparse.ArgumentParser, enabling suggestions for argument choicesand subparser names if mistyped by the user.(Contributed by Savannah Ostrowski ingh-124456.)

• Enable color for help text, which can be disabled with the optionalcolorparameter toargparse.ArgumentParser.This can also be controlled byenvironment variables.(Contributed by Hugo van Kemenade ingh-130645.)

ast¶

• Addcompare(), a function for comparing two ASTs.(Contributed by Batuhan Taskaya and Jeremy Hylton ingh-60191.)

• Add support forcopy.replace() for AST nodes.(Contributed by Bénédikt Tran ingh-121141.)

• Docstrings are now removed from an optimized AST in optimization level 2.(Contributed by Irit Katriel ingh-123958.)

• Therepr() output for AST nodes now includes more information.(Contributed by Tomas Roun ingh-116022.)

• When called with an AST as input, theparse() functionnow always verifies that the root node type is appropriate.(Contributed by Irit Katriel ingh-130139.)

• Add new options to the command-line interface:--feature-version,--optimize, and--show-empty.(Contributed by Semyon Moroz ingh-133367.)

asyncio¶

• The function and methods namedcreate_task() now take an arbitrarylist of keyword arguments. All keyword arguments are passed to theTask constructor or the custom task factory.(Seeset_task_factory() for details.)Thename andcontext keyword arguments are no longer special;the name should now be set using thename keyword argument of the factory,andcontext may beNone.

  This affects the following function and methods:asyncio.create_task(),asyncio.loop.create_task(),asyncio.TaskGroup.create_task().

  (Contributed by Thomas Grainger ingh-128307.)

• There are two new utility functions forintrospecting and printing a program’s call graph:capture_call_graph() andprint_call_graph().SeeAsyncio introspection capabilities for more details.(Contributed by Yury Selivanov, Pablo Galindo Salgado, and Łukasz Langaingh-91048.)

calendar¶

• By default, today’s date is highlighted in color incalendar’scommand-line text output.This can be controlled byenvironment variables.(Contributed by Hugo van Kemenade ingh-128317.)

concurrent.futures¶

• Add a new executor class,InterpreterPoolExecutor,which exposes multiple Python interpreters in the same process(‘subinterpreters’) to Python code.This uses a pool of independent Python interpreters to execute callsasynchronously.

  This is separate from the newinterpreters moduleintroduced byPEP 734.(Contributed by Eric Snow ingh-124548.)

• On Unix platforms other than macOS,‘forkserver’ is now the the defaultstartmethod forProcessPoolExecutor(replacing‘fork’).This change does not affect Windows or macOS, where‘spawn’ remains the default start method.

  If the threading incompatiblefork method is required, you must explicitlyrequest it by supplying a multiprocessing contextmp_context toProcessPoolExecutor.

  Seeforkserver restrictionsfor information and differences with thefork method and how this changemay affect existing code with mutable global shared variables and/or sharedobjects that can not be automaticallypickled.

  (Contributed by Gregory P. Smith ingh-84559.)

• Add two new methods toProcessPoolExecutor,terminate_workers()andkill_workers(),as ways to terminate or kill all living worker processes in the given pool.(Contributed by Charles Machalow ingh-130849.)

• Add the optionalbuffersize parameter toExecutor.map to limit the number of submittedtasks whose results have not yet been yielded. If the buffer is full,iteration over theiterables pauses until a result is yielded from thebuffer.(Contributed by Enzo Bonnal and Josh Rosenberg ingh-74028.)

configparser¶

• configparser will no longer write config files it cannot read,to improve security.Attempting towrite() keys containingdelimiters or beginning with the section header pattern will raise anInvalidWriteError.(Contributed by Jacob Lincoln ingh-129270.)

contextvars¶

• Support thecontext manager protocolforToken objects.(Contributed by Andrew Svetlov ingh-129889.)

ctypes¶

• The layout ofbit fieldsinStructure andUnion objectsis now a closer match to platform defaults (GCC/Clang or MSVC).In particular, fields no longer overlap.(Contributed by Matthias Görgens ingh-97702.)

• TheStructure._layout_ class attribute can now be setto help match a non-default ABI.(Contributed by Petr Viktorin ingh-97702.)

• The class ofStructure/Unionfield descriptors is now available asCField,and has new attributes to aid debugging and introspection.(Contributed by Petr Viktorin ingh-128715.)

• On Windows, theCOMError exception is now public.(Contributed by Jun Komoda ingh-126686.)

• On Windows, theCopyComPointer() function is now public.(Contributed by Jun Komoda ingh-127275.)

• Addmemoryview_at(), a function to create amemoryview object that refers to the supplied pointer andlength. This works likectypes.string_at() except it avoids abuffer copy, and is typically useful when implementing pure Pythoncallback functions that are passed dynamically-sized buffers.(Contributed by Rian Hunter ingh-112018.)

• Complex types,c_float_complex,c_double_complex, andc_longdouble_complex,are now available if both the compiler and thelibffi library supportcomplex C types.(Contributed by Sergey B Kirpichev ingh-61103.)

• Addctypes.util.dllist() for listing the shared librariesloaded by the current process.(Contributed by Brian Ward ingh-119349.)

• Movectypes.POINTER() types cache from a global internal cache(_pointer_type_cache) to the_CData.__pointer_type__ attribute of the correspondingctypes types.This will stop the cache from growing without limits in some situations.(Contributed by Sergey Miryanov ingh-100926.)

• Thepy_object type now supports subscription,making it ageneric type.(Contributed by Brian Schubert ingh-132168.)

• ctypes now supportsfree-threading builds.(Contributed by Kumar Aditya and Peter Bierma ingh-127945.)

curses¶

• Add theassume_default_colors() function,a refinement of theuse_default_colors() function whichallows changing the color pair0.(Contributed by Serhiy Storchaka ingh-133139.)

datetime¶

• Add thestrptime() method to thedatetime.date anddatetime.time classes.(Contributed by Wannes Boeykens ingh-41431.)

decimal¶

• AddDecimal.from_number() as an alternative constructor forDecimal.(Contributed by Serhiy Storchaka ingh-121798.)

• ExposeIEEEContext() to support creation of contextscorresponding to the IEEE 754 (2008) decimal interchange formats.(Contributed by Sergey B Kirpichev ingh-53032.)

difflib¶

• Comparison pages with highlighted changes generated by theHtmlDiff class now support ‘dark mode’.(Contributed by Jiahao Li ingh-129939.)

dis¶

• Add support for rendering full source location information ofinstructions, rather than only the line number.This feature is added to the following interfaces via theshow_positionskeyword argument:

  • dis.Bytecode

  • dis.dis()

  • dis.distb()

  • dis.disassemble()

  This feature is also exposed viadis--show-positions.(Contributed by Bénédikt Tran ingh-123165.)

• Add thedis--specialized command-line option toshow specialized bytecode.(Contributed by Bénédikt Tran ingh-127413.)

errno¶

• Add theEHWPOISON error code constant.(Contributed by James Roy ingh-126585.)

faulthandler¶

• Add support for printing the C stack trace on systems thatsupport it via the newdump_c_stack() function or via thec_stack argumentinfaulthandler.enable().(Contributed by Peter Bierma ingh-127604.)

fnmatch¶

• Addfilterfalse(), a function to reject namesmatching a given pattern.(Contributed by Bénédikt Tran ingh-74598.)

fractions¶

• AFraction object may now be constructed from anyobject with theas_integer_ratio() method.(Contributed by Serhiy Storchaka ingh-82017.)

• AddFraction.from_number() as an alternative constructor forFraction.(Contributed by Serhiy Storchaka ingh-121797.)

functools¶

• Add thePlaceholder sentinel.This may be used with thepartial()orpartialmethod() functions to reserve a placefor positional arguments in the returnedpartial object.(Contributed by Dominykas Grigonis ingh-119127.)

• Allow theinitial parameter ofreduce() to be passedas a keyword argument.(Contributed by Sayandip Dutta ingh-125916.)

getopt¶

• Add support for options with optional arguments.(Contributed by Serhiy Storchaka ingh-126374.)

• Add support for returning intermixed options and non-option arguments in order.(Contributed by Serhiy Storchaka ingh-126390.)

getpass¶

• Support keyboard feedback in thegetpass() function viathe keyword-only optional argumentecho_char.Placeholder characters are rendered whenever a character is entered,and removed when a character is deleted.(Contributed by Semyon Moroz ingh-77065.)

graphlib¶

• AllowTopologicalSorter.prepare() to be called more than onceas long as sorting has not started.(Contributed by Daniel Pope ingh-130914.)

heapq¶

• Theheapq module has improved support for working with max-heaps,via the following new functions:

  • heapify_max()

  • heappush_max()

  • heappop_max()

  • heapreplace_max()

  • heappushpop_max()

hmac¶

• Add a built-in implementation for HMAC (RFC 2104) using formally verifiedcode from theHACL* project.This implementation is used as a fallback when the OpenSSL implementationof HMAC is not available.(Contributed by Bénédikt Tran ingh-99108.)

http¶

• Directory lists and error pages generated by thehttp.servermodule allow the browser to apply its default dark mode.(Contributed by Yorik Hansen ingh-123430.)

• Thehttp.server module now supports serving over HTTPS using thehttp.server.HTTPSServer class. This functionality is exposed bythe command-line interface (python-mhttp.server) through the followingoptions:

  • --tls-cert<path>:Path to the TLS certificate file.

  • --tls-key<path>:Optional path to the private key file.

  • --tls-password-file<path>:Optional path to the password file for the private key.

  (Contributed by Semyon Moroz ingh-85162.)

imaplib¶

• AddIMAP4.idle(), implementing the IMAP4IDLE command as defined inRFC 2177.(Contributed by Forest ingh-55454.)

inspect¶

• signature() takes a new argumentannotation_format to controltheannotationlib.Format used for representing annotations.(Contributed by Jelle Zijlstra ingh-101552.)

• Signature.format() takes a new argumentunquote_annotations.If true, stringannotations are displayed withoutsurrounding quotes.(Contributed by Jelle Zijlstra ingh-101552.)

• Add functionispackage() to determine whether an object is apackage or not.(Contributed by Zhikang Yan ingh-125634.)

io¶

• Reading text from a non-blocking stream withread may now raise aBlockingIOError if the operation cannot immediately return bytes.(Contributed by Giovanni Siragusa ingh-109523.)

• Add theReader andWriter protocols as simpleralternatives to the pseudo-protocolstyping.IO,typing.TextIO, andtyping.BinaryIO.(Contributed by Sebastian Rittau ingh-127648.)

json¶

• Add exception notes for JSON serialization errors that allowidentifying the source of the error.(Contributed by Serhiy Storchaka ingh-122163.)

• Allow using thejson module as a script using the-m switch:python -m json.This is now preferred topython -m json.tool,which issoft deprecated.See theJSON command-line interface documentation.(Contributed by Trey Hunner ingh-122873.)

• By default, the output of theJSON command-line interface is highlighted in color.This can be controlled byenvironment variables.(Contributed by Tomas Roun ingh-131952.)

linecache¶

• getline() can now retrieve source code for frozen modules.(Contributed by Tian Gao ingh-131638.)

logging.handlers¶

• QueueListener objects now support thecontext manager protocol.(Contributed by Charles Machalow ingh-132106.)

• QueueListener.start nowraises aRuntimeError if the listener is already started.(Contributed by Charles Machalow ingh-132106.)

math¶

• Added more detailed error messages for domain errors in the module.(Contributed by Charlie Zhao and Sergey B Kirpichev ingh-101410.)

mimetypes¶

• Add a publiccommand-line for the module,invoked viapython -m mimetypes.(Contributed by Oleg Iarygin and Hugo van Kemenade ingh-93096.)

• Add several new MIME types based on RFCs and common usage:

  Microsoft andRFC 8081 MIME types for fonts

  • Embedded OpenType:application/vnd.ms-fontobject

  • OpenType Layout (OTF)font/otf

  • TrueType:font/ttf

  • WOFF 1.0font/woff

  • WOFF 2.0font/woff2

  RFC 9559 MIME types for Matroska audiovisualdata container structures

  • audio with no video:audio/matroska (.mka)

  • video:video/matroska (.mkv)

  • stereoscopic video:video/matroska-3d (.mk3d)

  Images with RFCs

  • RFC 1494: CCITT Group 3 (.g3)

  • RFC 3362: Real-time Facsimile, T.38 (.t38)

  • RFC 3745: JPEG 2000 (.jp2), extension (.jpx) and compound (.jpm)

  • RFC 3950: Tag Image File Format Fax eXtended, TIFF-FX (.tfx)

  • RFC 4047: Flexible Image Transport System (.fits)

  • RFC 7903: Enhanced Metafile (.emf) and Windows Metafile (.wmf)

  Other MIME type additions and changes

  • RFC 2361: Change type for.avi tovideo/vnd.aviand for.wav toaudio/vnd.wave

  • RFC 4337: Add MPEG-4audio/mp4 (.m4a)

  • RFC 5334: Add Ogg media (.oga,.ogg and.ogx)

  • RFC 6713: Add gzipapplication/gzip (.gz)

  • RFC 9639: Add FLACaudio/flac (.flac)

  • RFC 9512application/yaml MIME type for YAML files (.yamland.yml)

  • Add 7zapplication/x-7z-compressed (.7z)

  • Add Android Packageapplication/vnd.android.package-archive (.apk)when not strict

  • Add debapplication/x-debian-package (.deb)

  • Add glTF binarymodel/gltf-binary (.glb)

  • Add glTF JSON/ASCIImodel/gltf+json (.gltf)

  • Add M4Vvideo/x-m4v (.m4v)

  • Add PHPapplication/x-httpd-php (.php)

  • Add RARapplication/vnd.rar (.rar)

  • Add RPMapplication/x-rpm (.rpm)

  • Add STLmodel/stl (.stl)

  • Add Windows Media Videovideo/x-ms-wmv (.wmv)

  • De facto: Add WebMaudio/webm (.weba)

  • ECMA-376:Add.docx,.pptx and.xlsx types

  • OASIS:Add OpenDocument.odg,.odp,.ods and.odt types

  • W3C:Add EPUBapplication/epub+zip (.epub)

  (Contributed by Sahil Prajapati and Hugo van Kemenade ingh-84852,by Sasha “Nelie” Chernykh and Hugo van Kemenade ingh-132056,and by Hugo van Kemenade ingh-89416,gh-85957, andgh-129965.)

multiprocessing¶

• On Unix platforms other than macOS,‘forkserver’ is now the the defaultstartmethod(replacing‘fork’).This change does not affect Windows or macOS, where‘spawn’ remains the default start method.

  If the threading incompatiblefork method is required, you must explicitlyrequest it via a context fromget_context() (preferred)or change the default viaset_start_method().

  Seeforkserver restrictionsfor information and differences with thefork method and how this changemay affect existing code with mutable global shared variables and/or sharedobjects that can not be automaticallypickled.

  (Contributed by Gregory P. Smith ingh-84559.)

• multiprocessing’s'forkserver' start method now authenticatesits control socket to avoid solely relying on filesystem permissionsto restrict what other processes could cause the forkserver to spawn workersand run code.(Contributed by Gregory P. Smith forgh-97514.)

• Themultiprocessing proxy objectsforlist anddict types gain previously overlooked missing methods:

  • clear() andcopy() for proxies oflist

  • fromkeys(),reversed(d),d|{},{}|d,d|={'b':2} for proxies ofdict

  (Contributed by Roy Hyunjin Han forgh-103134.)

• Add support for sharedset objects viaSyncManager.set().Theset() inManager() method is now available.(Contributed by Mingyu Park ingh-129949.)

• Add theinterrupt()tomultiprocessing.Process objects, which terminates the childprocess by sendingSIGINT. This enablesfinally clauses to print a stack trace for the terminatedprocess. (Contributed by Artem Pulkin ingh-131913.)

operator¶

• Addis_none() andis_not_none() as a pairof functions, such thatoperator.is_none(obj) is equivalenttoobjisNone andoperator.is_not_none(obj) is equivalenttoobjisnotNone.(Contributed by Raymond Hettinger and Nico Mexis ingh-115808.)

os¶

• Add thereload_environ() function to updateos.environ andos.environb with changes to the environment made byos.putenv(), byos.unsetenv(), or made outside Python in thesame process.(Contributed by Victor Stinner ingh-120057.)

• Add theSCHED_DEADLINE andSCHED_NORMAL constantsto theos module.(Contributed by James Roy ingh-127688.)

• Add thereadinto() function to read into abuffer object from a file descriptor.(Contributed by Cody Maloney ingh-129205.)

os.path¶

• Thestrict parameter torealpath() accepts a new value,ALLOW_MISSING.If used, errors other thanFileNotFoundError will be re-raised;the resulting path can be missing but it will be free of symlinks.(Contributed by Petr Viktorin forCVE 2025-4517.)

pathlib¶

• Add methods topathlib.Path to recursively copy or move files anddirectories:

  • copy() copies a file or directory tree to a destination.

  • copy_into() copiesinto a destination directory.

  • move() moves a file or directory tree to a destination.

  • move_into() movesinto a destination directory.

  (Contributed by Barney Gale ingh-73991.)

• Add theinfo attribute, which stores an objectimplementing the newpathlib.types.PathInfo protocol. Theobject supports querying the file type and internally cachingstat() results. Path objects generated byiterdir() are initialized with file type informationgleaned from scanning the parent directory.(Contributed by Barney Gale ingh-125413.)

pdb¶

• Thepdb module now supports remote attaching to a running Python processusing a new-pPID command-line option:

  python-mpdb-p1234

  This will connect to the Python process with the given PID and allow you todebug it interactively. Notice that due to how the Python interpreter worksattaching to a remote process that is blocked in a system call or waiting forI/O will only work once the next bytecode instruction is executed or when theprocess receives a signal.

  This feature usesPEP 768and the newsys.remote_exec() function to attach to the remote processand send the PDB commands to it.

  (Contributed by Matt Wozniski and Pablo Galindo ingh-131591.)

• Hardcoded breakpoints (breakpoint() andset_trace()) nowreuse the most recentPdb instance that callsset_trace(), instead of creating a new one each time.As a result, all the instance specific data likedisplay andcommands are preserved across hardcoded breakpoints.(Contributed by Tian Gao ingh-121450.)

• Add a new argumentmode topdb.Pdb. Disable therestartcommand whenpdb is ininline mode.(Contributed by Tian Gao ingh-123757.)

• A confirmation prompt will be shown when the user tries to quitpdbininline mode.y,Y,<Enter> orEOF will confirmthe quit and callsys.exit(), instead of raisingbdb.BdbQuit.(Contributed by Tian Gao ingh-124704.)

• Inline breakpoints likebreakpoint() orpdb.set_trace() willalways stop the program at calling frame, ignoring theskip pattern(if any).(Contributed by Tian Gao ingh-130493.)

• <tab> at the beginning of the line inpdb multi-line input willfill in a 4-space indentation now, instead of inserting a\t character.(Contributed by Tian Gao ingh-130471.)

• Auto-indent is introduced inpdb multi-line input. It will eitherkeep the indentation of the last line or insert a 4-space indentation whenit detects a new code block.(Contributed by Tian Gao ingh-133350.)

• $_asynctask is added to access the current asyncio task if applicable.(Contributed by Tian Gao ingh-124367.)

• pdb.set_trace_async() is added to support debugging asynciocoroutines.await statements are supported with thisfunction.(Contributed by Tian Gao ingh-132576.)

• Source code displayed inpdb will be syntax-highlighted. This featurecan be controlled using the same methods as the defaultinteractiveshell, in addition to the newly addedcolorize argument ofpdb.Pdb.(Contributed by Tian Gao and Łukasz Langa ingh-133355.)

pickle¶

• Set the default protocol version on thepickle module to 5.For more details, seepickle protocols.

• Add exception notes for pickle serialization errors that allowidentifying the source of the error.(Contributed by Serhiy Storchaka ingh-122213.)

platform¶

• Addinvalidate_caches(), a function to invalidatecached results in theplatform module.(Contributed by Bénédikt Tran ingh-122549.)

pydoc¶

• Annotations in help output are now usuallydisplayed in a format closer to that in the original source.(Contributed by Jelle Zijlstra ingh-101552.)

re¶

• Support\z as a synonym for\Z inregularexpressions.It is interpreted unambiguously in many other regular expression engines,unlike\Z, which has subtly different behavior.(Contributed by Serhiy Storchaka ingh-133306.)

• \B inregularexpression now matches the empty input string,meaning that it is now always the opposite of\b.(Contributed by Serhiy Storchaka ingh-124130.)

socket¶

• Improve and fix support for Bluetooth sockets.

  • Fix support of Bluetooth sockets on NetBSD and DragonFly BSD.(Contributed by Serhiy Storchaka ingh-132429.)

  • Fix support forBTPROTO_HCI on FreeBSD.(Contributed by Victor Stinner ingh-111178.)

  • Add support forBTPROTO_SCO on FreeBSD.(Contributed by Serhiy Storchaka ingh-85302.)

  • Add support forcid andbdaddr_type in the address forBTPROTO_L2CAP on FreeBSD.(Contributed by Serhiy Storchaka ingh-132429.)

  • Add support forchannel in the address forBTPROTO_HCI on Linux.(Contributed by Serhiy Storchaka ingh-70145.)

  • Accept an integer as the address forBTPROTO_HCI on Linux.(Contributed by Serhiy Storchaka ingh-132099.)

  • Returncid ingetsockname() forBTPROTO_L2CAP.(Contributed by Serhiy Storchaka ingh-132429.)

  • Add many new constants.(Contributed by Serhiy Storchaka ingh-132734.)

ssl¶

• Indicate through theHAS_PHA Boolean whether thesslmodule supports TLSv1.3 post-handshake client authentication (PHA).(Contributed by Will Childs-Klein ingh-128036.)

struct¶

• Support thefloatcomplex anddoublecomplex C types inthestruct module (formatting characters'F' and'D'respectively).(Contributed by Sergey B Kirpichev ingh-121249.)

symtable¶

• Expose the followingSymbol methods:

  • is_comp_cell()

  • is_comp_iter()

  • is_free_class()

  (Contributed by Bénédikt Tran ingh-120029.)

sys¶

• The previously undocumented special functionsys.getobjects(),which only exists in specialized builds of Python, may now return objectsfrom other interpreters than the one it’s called in.(Contributed by Eric Snow ingh-125286.)

• Addsys._is_immortal() for determining if an object isimmortal.(Contributed by Peter Bierma ingh-128509.)

• On FreeBSD,sys.platform no longer contains the major version number.It is always'freebsd', instead of'freebsd13' or'freebsd14'.(Contributed by Michael Osipov ingh-129393.)

• RaiseDeprecationWarning forsys._clear_type_cache(). Thisfunction was deprecated in Python 3.13 but it didn’t raise a runtime warning.

• Addsys.remote_exec() to implement the new external debugger interface.SeePEP 768 for details.(Contributed by Pablo Galindo Salgado, Matt Wozniski, and Ivona Stojanovicingh-131591.)

• Add thesys._jit namespace, containing utilities for introspectingjust-in-time compilation.(Contributed by Brandt Bucher ingh-133231.)

sys.monitoring¶

• Add two new monitoring events,BRANCH_LEFT andBRANCH_RIGHT.These replace and deprecate theBRANCH event.(Contributed by Mark Shannon ingh-122548.)

sysconfig¶

• AddABIFLAGS key toget_config_vars() on Windows.(Contributed by Xuehai Pan ingh-131799.)

tarfile¶

• data_filter() now normalizes symbolic link targets in order toavoid path traversal attacks.(Contributed by Petr Viktorin ingh-127987 andCVE 2025-4138.)

• extractall() now skips fixing up directory attributeswhen a directory was removed or replaced by another kind of file.(Contributed by Petr Viktorin ingh-127987 andCVE 2024-12718.)

• extract() andextractall()now (re-)apply the extraction filter when substituting a link (hard orsymbolic) with a copy of another archive member, and when fixing updirectory attributes.The former raises a new exception,LinkFallbackError.(Contributed by Petr Viktorin forCVE 2025-4330 andCVE 2024-12718.)

• extract() andextractall()no longer extract rejected members whenerrorlevel() is zero.(Contributed by Matt Prodani and Petr Viktorin ingh-112887andCVE 2025-4435.)

threading¶

• threading.Thread.start() now sets the operating system thread nametothreading.Thread.name.(Contributed by Victor Stinner ingh-59705.)

tkinter¶

• Maketkinter widget methodsafter() andafter_idle()accept keyword arguments.(Contributed by Zhikang Yan ingh-126899.)

• Add ability to specify a name fortkinter.OptionMenu andtkinter.ttk.OptionMenu.(Contributed by Zhikang Yan ingh-130482.)

turtle¶

• Add context managers forturtle.fill(),turtle.poly(),andturtle.no_animation().(Contributed by Marie Roald and Yngve Mardal Moe ingh-126350.)

types¶

• types.UnionType is now an alias fortyping.Union.Seebelow for more details.(Contributed by Jelle Zijlstra ingh-105499.)

typing¶

• Thetypes.UnionType andtyping.Union types are nowaliases for each other, meaning that both old-style unions(created withUnion[int,str]) and new-style unions (int|str)now create instances of the same runtime type. This unifies the behaviorbetween the two syntaxes, but leads to some differences in behavior thatmay affect users who introspect types at runtime:

  • Both syntaxes for creating a union now produce the same stringrepresentation inrepr().For example,repr(Union[int,str]) is now"int|str" instead of"typing.Union[int,str]".

  • Unions created using the old syntax are no longer cached.Previously, runningUnion[int,str] multiple times would returnthe same object (Union[int,str]isUnion[int,str] would beTrue),but now it will return two different objects.Use== to compare unions for equality, notis.New-style unions have never been cached this way.This change could increase memory usage for some programs that usea large number of unions created by subscriptingtyping.Union.However, several factors offset this cost:unions used in annotations are no longer evaluated by default in Python3.14 because ofPEP 649; an instance oftypes.UnionType isitself much smaller than the object returned byUnion[] was on priorPython versions; and removing the cache also saves some space.It is therefore unlikely that this change will cause a significant increasein memory usage for most users.

  • Previously, old-style unions were implemented using the private classtyping._UnionGenericAlias.This class is no longer needed for the implementation,but it has been retained for backward compatibility,with removal scheduled for Python 3.17.Users should use documented introspection helpers likeget_origin() andtyping.get_args() instead ofrelying on private implementation details.

  • It is now possible to usetyping.Union itself inisinstance() checks.For example,isinstance(int|str,typing.Union) will returnTrue;previously this raisedTypeError.

  • The__args__ attribute oftyping.Union objects isno longer writable.

  • It is no longer possible to set any attributes onUnionobjects.This only ever worked for dunder attributes on previous versions, was neverdocumented to work, and was subtly broken in many cases.

  (Contributed by Jelle Zijlstra ingh-105499.)

• TypeAliasType now supports star unpacking.

unicodedata¶

• The Unicode database has been updated to Unicode 16.0.0.

unittest¶

• unittest output is now colored by default.This can be controlled byenvironment variables.(Contributed by Hugo van Kemenade ingh-127221.)

• unittest discovery supportsnamespace package as startdirectory again. It was removed in Python 3.11.(Contributed by Jacob Walls ingh-80958.)

• A number of new methods were added in theTestCase classthat provide more specialized tests.

  • assertHasAttr() andassertNotHasAttr() check whether the objecthas a particular attribute.

  • assertIsSubclass() andassertNotIsSubclass() check whether the objectis a subclass of a particular class, or of one of a tuple of classes.

  • assertStartsWith(),assertNotStartsWith(),assertEndsWith() andassertNotEndsWith() check whether the Unicodeor byte string starts or ends with particular strings.

  (Contributed by Serhiy Storchaka ingh-71339.)

urllib¶

• Upgrade HTTP digest authentication algorithm forurllib.request bysupporting SHA-256 digest authentication as specified inRFC 7616.(Contributed by Calvin Bui ingh-128193.)

• Improve ergonomics and standards compliance when parsing and emittingfile: URLs.

  Inurl2pathname():

  • Accept a complete URL when the newrequire_scheme argument is set totrue.

  • Discard URL authority if it matches the local hostname.

  • Discard URL authority if it resolves to a local IP address when the newresolve_host argument is set to true.

  • Discard URL query and fragment components.

  • RaiseURLError if a URL authority isn’t local,except on Windows where we return a UNC path as before.

  Inpathname2url():

  • Return a complete URL when the newadd_scheme argument is set to true.

  • Include an empty URL authority when a path begins with a slash. Forexample, the path/etc/hosts is converted to the URL///etc/hosts.

  On Windows, drive letters are no longer converted to uppercase, and:characters not following a drive letter no longer cause anOSErrorexception to be raised.

  (Contributed by Barney Gale ingh-125866.)

uuid¶

• Add support for UUID versions 6, 7, and 8 viauuid6(),uuid7(), anduuid8() respectively, as specifiedinRFC 9562.(Contributed by Bénédikt Tran ingh-89083.)

• NIL andMAX are now available to represent theNil and Max UUID formats as defined byRFC 9562.(Contributed by Nick Pope ingh-128427.)

• Allow generating multiple UUIDs simultaneously on the command-line viapython-muuid--count.(Contributed by Simon Legner ingh-131236.)

webbrowser¶

• Names in theBROWSER environment variable can now refer to alreadyregistered browsers for thewebbrowser module, instead of alwaysgenerating a new browser command.

  This makes it possible to setBROWSER to the value of one of thesupported browsers on macOS.

zipfile¶

• AddedZipInfo._for_archive, a methodto resolve suitable defaults for aZipInfo objectas used byZipFile.writestr.(Contributed by Bénédikt Tran ingh-123424.)

• ZipFile.writestr() now respects theSOURCE_DATE_EPOCHenvironment variable in order to better support reproducible builds.(Contributed by Jiahao Li ingh-91279.)

asyncio¶

• Standard benchmark results have improved by 10-20% following theimplementation of a new per-thread doubly linked listfornativetasks,also reducing memory usage.This enables external introspection tools such aspython -m asyncio pstreeto introspect the call graph of asyncio tasks running in all threads.(Contributed by Kumar Aditya ingh-107803.)

• The module now has first class support forfree-threading builds.This enables parallel execution of multiple event loops acrossdifferent threads, scaling linearly with the number of threads.(Contributed by Kumar Aditya ingh-128002.)

base64¶

• b16decode() is now up to six times faster.(Contributed by Bénédikt Tran, Chris Markiewicz, and Adam Turneringh-118761.)

bdb¶

• The basic debugger now has asys.monitoring-based backend,which can be selected via the passing'monitoring'to theBdb class’s newbackend parameter.(Contributed by Tian Gao ingh-124533.)

difflib¶

• TheIS_LINE_JUNK() function is now up to twice as fast.(Contributed by Adam Turner and Semyon Moroz ingh-130167.)

gc¶

• The newincremental garbage collectormeans that maximum pause times are reducedby an order of magnitude or more for larger heaps.

  Because of this optimization, the meaning of the results ofget_threshold() andset_threshold() have changed,along withget_count() andget_stats().

  • For backwards compatibility,get_threshold() continues to returna three-item tuple.The first value is the threshold for young collections, as before;the second value determines the rate at which the old collection is scanned(the default is 10, and higher values mean that the old collectionis scanned more slowly).The third value is now meaningless and is always zero.

  • set_threshold() now ignores any items after the second.

  • get_count() andget_stats() continue to returnthe same format of results.The only difference is that instead of the results referring tothe young, aging and old generations,the results refer to the young generationand the aging and collecting spaces of the old generation.

  In summary, code that attempted to manipulate the behavior of the cycle GCmay not work exactly as intended, but it is very unlikely to be harmful.All other code will work just fine.

  (Contributed by Mark Shannon ingh-108362.)

io¶

• Opening and reading files now executes fewer system calls.Reading a small operating system cached file in full is up to 15% faster.(Contributed by Cody Maloney and Victor Stinneringh-120754 andgh-90102.)

pathlib¶

• Path.read_bytes now uses unbuffered modeto open files, which is between 9% and 17% faster to read in full.(Contributed by Cody Maloney ingh-120754.)

pdb¶

• pdb now supports two backends, based on eithersys.settrace() orsys.monitoring.Using thepdb CLI orbreakpoint()will always use thesys.monitoring backend.Explicitly instantiatingpdb.Pdb and its derived classeswill use thesys.settrace() backend by default, which is configurable.(Contributed by Tian Gao ingh-124533.)

uuid¶

• uuid3() anduuid5() are now both roughly 40% fasterfor 16-byte names and 20% faster for 1024-byte names.Performance for longer names remains unchanged.(Contributed by Bénédikt Tran ingh-128150.)

• uuid4() is now c. 30% faster.(Contributed by Bénédikt Tran ingh-128150.)

zlib¶

• On Windows,zlib-ngis now used as the implementation of thezlib modulein the default binaries.There are no known incompatibilities betweenzlib-ngand the previously-usedzlib implementation.This should result in better performance at all compression levels.

  It is worth noting thatzlib.Z_BEST_SPEED (1) may result insignificantly less compression than the previous implementation,whilst also significantly reducing the time taken to compress.

  (Contributed by Steve Dower ingh-91349.)

argparse¶

• Remove thetype,choices, andmetavar parametersofBooleanOptionalAction.These have been deprecated since Python 3.12.(Contributed by Nikita Sobolev ingh-118805.)

• Callingadd_argument_group()on an argument group now raises aValueError.Similarly,add_argument_group()oradd_mutually_exclusive_group()on a mutually exclusive group now both raiseValueErrors.This ‘nesting’ was never supported, often failed to work correctly,and was unintentionally exposed through inheritance.This functionality has been deprecated since Python 3.11.(Contributed by Savannah Ostrowski ingh-127186.)

ast¶

• Remove the following classes, which have been deprecated aliases ofConstant since Python 3.8 and have emitteddeprecation warnings since Python 3.12:

  • Bytes

  • Ellipsis

  • NameConstant

  • Num

  • Str

  As a consequence of these removals, user-definedvisit_Num,visit_Str,visit_Bytes,visit_NameConstant andvisit_Ellipsis methodson customNodeVisitor subclasses will no longer be calledwhen theNodeVisitor subclass is visiting an AST.Define avisit_Constant method instead.

  (Contributed by Alex Waygood ingh-119562.)

• Remove the following deprecated properties onast.Constant,which were present for compatibility with the now-removed AST classes:

  • Constant.n

  • Constant.s

  UseConstant.value instead.(Contributed by Alex Waygood ingh-119562.)

asyncio¶

• Remove the following classes, methods, and functions,which have been deprecated since Python 3.12:

  • AbstractChildWatcher

  • FastChildWatcher

  • MultiLoopChildWatcher

  • PidfdChildWatcher

  • SafeChildWatcher

  • ThreadedChildWatcher

  • AbstractEventLoopPolicy.get_child_watcher()

  • AbstractEventLoopPolicy.set_child_watcher()

  • get_child_watcher()

  • set_child_watcher()

  (Contributed by Kumar Aditya ingh-120804.)

• asyncio.get_event_loop() now raises aRuntimeErrorif there is no current event loop,and no longer implicitly creates an event loop.

  (Contributed by Kumar Aditya ingh-126353.)

  There’s a few patterns that useasyncio.get_event_loop(), mostof them can be replaced withasyncio.run().

  If you’re running an async function, simply useasyncio.run().

  Before:

  asyncdefmain():...loop=asyncio.get_event_loop()try:loop.run_until_complete(main())finally:loop.close()

  After:

  asyncdefmain():...asyncio.run(main())

  If you need to start something, for example, a server listening on a socketand then run forever, useasyncio.run() and anasyncio.Event.

  Before:

  defstart_server(loop):...loop=asyncio.get_event_loop()try:start_server(loop)loop.run_forever()finally:loop.close()

  After:

  defstart_server(loop):...asyncdefmain():start_server(asyncio.get_running_loop())awaitasyncio.Event().wait()asyncio.run(main())

  If you need to run something in an event loop, then run some blockingcode around it, useasyncio.Runner.

  Before:

  asyncdefoperation_one():...defblocking_code():...asyncdefoperation_two():...loop=asyncio.get_event_loop()try:loop.run_until_complete(operation_one())blocking_code()loop.run_until_complete(operation_two())finally:loop.close()

  After:

  asyncdefoperation_one():...defblocking_code():...asyncdefoperation_two():...withasyncio.Runner()asrunner:runner.run(operation_one())blocking_code()runner.run(operation_two())

email¶

• Removeemail.utils.localtime()’sisdst parameter,which was deprecated in and has been ignored since Python 3.12.(Contributed by Hugo van Kemenade ingh-118798.)

importlib.abc¶

• Remove deprecatedimportlib.abc classes:

  • ResourceReader(useTraversableResources)

  • Traversable(useTraversable)

  • TraversableResources(useTraversableResources)

  (Contributed by Jason R. Coombs and Hugo van Kemenade ingh-93963.)

itertools¶

• Remove support for copy, deepcopy, and pickle operationsfromitertools iterators.These have emitted aDeprecationWarning since Python 3.12.(Contributed by Raymond Hettinger ingh-101588.)

pathlib¶

• Remove support for passing additional keyword argumentstoPath.In previous versions, any such arguments are ignored.(Contributed by Barney Gale ingh-74033.)

• Remove support for passing additional positional arguments toPurePath.relative_to() andis_relative_to().In previous versions, any such arguments are joined ontoother.(Contributed by Barney Gale ingh-78707.)

pkgutil¶

• Remove theget_loader() andfind_loader() functions,which have been deprecated since Python 3.12.(Contributed by Bénédikt Tran ingh-97850.)

pty¶

• Remove themaster_open() andslave_open() functions,which have been deprecated since Python 3.12.Usepty.openpty() instead.(Contributed by Nikita Sobolev ingh-118824.)

sqlite3¶

• Removeversion andversion_info fromthesqlite3 module;usesqlite_version andsqlite_version_infofor the actual version number of the runtime SQLite library.(Contributed by Hugo van Kemenade ingh-118924.)

• Using a sequence of parameters with named placeholders nowraises aProgrammingError,having been deprecated since Python 3.12.(Contributed by Erlend E. Aasland ingh-118928 andgh-101693.)

urllib¶

• Remove theQuoter class fromurllib.parse,which has been deprecated since Python 3.11.(Contributed by Nikita Sobolev ingh-118827.)

• Remove theURLopener andFancyURLopener classesfromurllib.request,which have been deprecated since Python 3.3.

  myopener.open() can be replaced withurlopen().myopener.retrieve() can be replaced withurlretrieve().Customisations to the opener classes can be replaced by passingcustomized handlers tobuild_opener().(Contributed by Barney Gale ingh-84850.)

New deprecations¶

• Passing a complex number as thereal orimag argument in thecomplex() constructor is now deprecated;complex numbers should only be passed as a single positional argument.(Contributed by Serhiy Storchaka ingh-109218.)

• argparse:

  • Passing the undocumented keyword argumentprefix_chars to theadd_argument_group() method is now deprecated.(Contributed by Savannah Ostrowski ingh-125563.)

  • Deprecated theargparse.FileType type converter.Anything relating to resource management should be handleddownstream, after the arguments have been parsed.(Contributed by Serhiy Storchaka ingh-58032.)

• asyncio:

  • Theasyncio.iscoroutinefunction() is now deprecatedand will be removed in Python 3.16;useinspect.iscoroutinefunction() instead.(Contributed by Jiahao Li and Kumar Aditya ingh-122875.)

  • Theasyncio policy system is deprecatedand will be removed in Python 3.16.In particular, the following classes and functions are deprecated:

    • asyncio.AbstractEventLoopPolicy

    • asyncio.DefaultEventLoopPolicy

    • asyncio.WindowsSelectorEventLoopPolicy

    • asyncio.WindowsProactorEventLoopPolicy

    • asyncio.get_event_loop_policy()

    • asyncio.set_event_loop_policy()

    Users should useasyncio.run() orasyncio.Runner withtheloop_factory argument to use the desired event loop implementation.

    For example, to useasyncio.SelectorEventLoop on Windows:

    importasyncioasyncdefmain():...asyncio.run(main(),loop_factory=asyncio.SelectorEventLoop)

    (Contributed by Kumar Aditya ingh-127949.)

• codecs:Thecodecs.open() function is now deprecated,and will be removed in a future version of Python.Useopen() instead.(Contributed by Inada Naoki ingh-133036.)

• ctypes:

  • On non-Windows platforms, settingStructure._pack_ to use aMSVC-compatible default memory layout is now deprecated in favor of settingStructure._layout_ to'ms', and will be removed in Python 3.19.(Contributed by Petr Viktorin ingh-131747.)

  • Callingctypes.POINTER() on a string is now deprecated.Useincomplete typesfor self-referential structures.Also, the internalctypes._pointer_type_cache is deprecated.Seectypes.POINTER() for updated implementation details.(Contributed by Sergey Myrianov ingh-100926.)

• functools:Calling the Python implementation offunctools.reduce() withfunctionorsequence as keyword arguments is now deprecated;the parameters will be made positional-only in Python 3.16.(Contributed by Kirill Podoprigora ingh-121676.)

• logging:Support for custom logging handlers with thestrm argumentis now deprecated and scheduled for removal in Python 3.16.Define handlers with thestream argument instead.(Contributed by Mariusz Felisiak ingh-115032.)

• mimetypes:Valid extensions are either empty or must start with ‘.’ formimetypes.MimeTypes.add_type().Undotted extensions are deprecated and willraise aValueError in Python 3.16.(Contributed by Hugo van Kemenade ingh-75223.)

• nturl2path:This module is now deprecated. Callurllib.request.url2pathname()andpathname2url() instead.(Contributed by Barney Gale ingh-125866.)

• os:Theos.popen() andos.spawn* functionsare nowsoft deprecated.They should no longer be used to write new code.Thesubprocess module is recommended instead.(Contributed by Victor Stinner ingh-120743.)

• pathlib:pathlib.PurePath.as_uri() is now deprecatedand scheduled for removal in Python 3.19.Usepathlib.Path.as_uri() instead.(Contributed by Barney Gale ingh-123599.)

• pdb:The undocumentedpdb.Pdb.curframe_locals attribute is now a deprecatedread-only property, which will be removed in a future version of Python.The low overhead dynamic frame locals access added in Python 3.13 byPEP 667means the frame locals cache reference previously stored in this attributeis no longer needed. Derived debuggers should accesspdb.Pdb.curframe.f_locals directly in Python 3.13 and later versions.(Contributed by Tian Gao ingh-124369 andgh-125951.)

• symtable:Deprecatesymtable.Class.get_methods() due to the lack of interest,scheduled for removal in Python 3.16.(Contributed by Bénédikt Tran ingh-119698.)

• tkinter:Thetkinter.Variable methodstrace_variable(),trace_vdelete() andtrace_vinfo() are now deprecated.Usetrace_add(),trace_remove() andtrace_info() instead.(Contributed by Serhiy Storchaka ingh-120220.)

• urllib.parse:Accepting objects with false values (like0 and[]) except emptystrings, bytes-like objects andNone inparse_qsl()andparse_qs() is now deprecated.(Contributed by Serhiy Storchaka ingh-116897.)

Pending removal in Python 3.15¶

• The import system:

  • Setting__cached__ on a module whilefailing to set__spec__.cachedis deprecated. In Python 3.15,__cached__ will cease to be set ortake into consideration by the import system or standard library. (gh-97879)

  • Setting__package__ on a module whilefailing to set__spec__.parentis deprecated. In Python 3.15,__package__ will cease to be set ortake into consideration by the import system or standard library. (gh-97879)

• ctypes:

  • The undocumentedctypes.SetPointerType() functionhas been deprecated since Python 3.13.

• http.server:

  • The obsolete and rarely usedCGIHTTPRequestHandlerhas been deprecated since Python 3.13.No direct replacement exists.Anything is better than CGI to interfacea web server with a request handler.

  • The--cgi flag to thepython -m http.servercommand-line interface has been deprecated since Python 3.13.

• importlib:

  • load_module() method: useexec_module() instead.

• locale:

  • Thegetdefaultlocale() functionhas been deprecated since Python 3.11.Its removal was originally planned for Python 3.13 (gh-90817),but has been postponed to Python 3.15.Usegetlocale(),setlocale(),andgetencoding() instead.(Contributed by Hugo van Kemenade ingh-111187.)

• pathlib:

  • .PurePath.is_reserved()has been deprecated since Python 3.13.Useos.path.isreserved() to detect reserved paths on Windows.

• platform:

  • platform.java_ver() has been deprecated since Python 3.13.This function is only useful for Jython support, has a confusing API,and is largely untested.

• sysconfig:

  • Thecheck_home argument ofsysconfig.is_python_build() has beendeprecated since Python 3.12.

• threading:

  • RLock() will take no arguments in Python 3.15.Passing any arguments has been deprecated since Python 3.14,as the Python version does not permit any arguments,but the C version allows any number of positional or keyword arguments,ignoring every argument.

• types:

  • types.CodeType: Accessingco_lnotab wasdeprecated inPEP 626since 3.10 and was planned to be removed in 3.12,but it only got a properDeprecationWarning in 3.12.May be removed in 3.15.(Contributed by Nikita Sobolev ingh-101866.)

• typing:

  • The undocumented keyword argument syntax for creatingNamedTuple classes(for example,Point=NamedTuple("Point",x=int,y=int))has been deprecated since Python 3.13.Use the class-based syntax or the functional syntax instead.

  • When using the functional syntax ofTypedDicts, failingto pass a value to thefields parameter (TD=TypedDict("TD")) orpassingNone (TD=TypedDict("TD",None)) has been deprecatedsince Python 3.13.UseclassTD(TypedDict):pass orTD=TypedDict("TD",{})to create a TypedDict with zero field.

  • Thetyping.no_type_check_decorator() decorator functionhas been deprecated since Python 3.13.After eight years in thetyping module,it has yet to be supported by any major type checker.

• sre_compile,sre_constants andsre_parse modules.

• wave:

  • Thegetmark(),setmark() andgetmarkers() methods oftheWave_read andWave_write classeshave been deprecated since Python 3.13.

• zipimport:

  • zipimport.zipimporter.load_module() has been deprecated sincePython 3.10. Useexec_module() instead.(gh-125746.)

Pending removal in Python 3.16¶

• The import system:

  • Setting__loader__ on a module whilefailing to set__spec__.loaderis deprecated. In Python 3.16,__loader__ will cease to be set ortaken into consideration by the import system or the standard library.

• array:

  • The'u' format code (wchar_t)has been deprecated in documentation since Python 3.3and at runtime since Python 3.13.Use the'w' format code (Py_UCS4)for Unicode characters instead.

• asyncio:

  • asyncio.iscoroutinefunction() is deprecatedand will be removed in Python 3.16;useinspect.iscoroutinefunction() instead.(Contributed by Jiahao Li and Kumar Aditya ingh-122875.)

  • asyncio policy system is deprecated and will be removed in Python 3.16.In particular, the following classes and functions are deprecated:

    • asyncio.AbstractEventLoopPolicy

    • asyncio.DefaultEventLoopPolicy

    • asyncio.WindowsSelectorEventLoopPolicy

    • asyncio.WindowsProactorEventLoopPolicy

    • asyncio.get_event_loop_policy()

    • asyncio.set_event_loop_policy()

    Users should useasyncio.run() orasyncio.Runner withloop_factory to use the desired event loop implementation.

    For example, to useasyncio.SelectorEventLoop on Windows:

    importasyncioasyncdefmain():...asyncio.run(main(),loop_factory=asyncio.SelectorEventLoop)

    (Contributed by Kumar Aditya ingh-127949.)

• builtins:

  • Bitwise inversion on boolean types,~True or~Falsehas been deprecated since Python 3.12,as it produces surprising and unintuitive results (-2 and-1).Usenotx instead for the logical negation of a Boolean.In the rare case that you need the bitwise inversion ofthe underlying integer, convert toint explicitly (~int(x)).

• functools:

  • Calling the Python implementation offunctools.reduce() withfunctionorsequence as keyword arguments has been deprecated since Python 3.14.

• logging:

  Support for custom logging handlers with thestrm argument is deprecatedand scheduled for removal in Python 3.16. Define handlers with thestreamargument instead. (Contributed by Mariusz Felisiak ingh-115032.)

• mimetypes:

  • Valid extensions start with a ‘.’ or are empty formimetypes.MimeTypes.add_type().Undotted extensions are deprecated and willraise aValueError in Python 3.16.(Contributed by Hugo van Kemenade ingh-75223.)

• shutil:

  • TheExecError exceptionhas been deprecated since Python 3.14.It has not been used by any function inshutil since Python 3.4,and is now an alias ofRuntimeError.

• symtable:

  • TheClass.get_methods methodhas been deprecated since Python 3.14.

• sys:

  • The_enablelegacywindowsfsencoding() functionhas been deprecated since Python 3.13.Use thePYTHONLEGACYWINDOWSFSENCODING environment variable instead.

• sysconfig:

  • Thesysconfig.expand_makefile_vars() functionhas been deprecated since Python 3.14.Use thevars argument ofsysconfig.get_paths() instead.

• tarfile:

  • The undocumented and unusedTarFile.tarfile attributehas been deprecated since Python 3.13.

Pending removal in Python 3.17¶

• collections.abc:

  • collections.abc.ByteString is scheduled for removal in Python 3.17.

    Useisinstance(obj,collections.abc.Buffer) to test ifobjimplements thebuffer protocol at runtime. For usein type annotations, either useBuffer or a unionthat explicitly specifies the types your code supports (e.g.,bytes|bytearray|memoryview).

    ByteString was originally intended to be an abstract class thatwould serve as a supertype of bothbytes andbytearray.However, since the ABC never had any methods, knowing that an object was aninstance ofByteString never actually told you anything usefulabout the object. Other common buffer types such asmemoryviewwere also never understood as subtypes ofByteString (either atruntime or by static type checkers).

    SeePEP 688 for more details.(Contributed by Shantanu Jain ingh-91896.)

• typing:

  • Before Python 3.14, old-style unions were implemented using the private classtyping._UnionGenericAlias. This class is no longer needed for the implementation,but it has been retained for backward compatibility, with removal scheduled for Python3.17. Users should use documented introspection helpers liketyping.get_origin()andtyping.get_args() instead of relying on private implementation details.

  • typing.ByteString, deprecated since Python 3.9, is scheduled for removal inPython 3.17.

    Useisinstance(obj,collections.abc.Buffer) to test ifobjimplements thebuffer protocol at runtime. For usein type annotations, either useBuffer or a unionthat explicitly specifies the types your code supports (e.g.,bytes|bytearray|memoryview).

    ByteString was originally intended to be an abstract class thatwould serve as a supertype of bothbytes andbytearray.However, since the ABC never had any methods, knowing that an object was aninstance ofByteString never actually told you anything usefulabout the object. Other common buffer types such asmemoryviewwere also never understood as subtypes ofByteString (either atruntime or by static type checkers).

    SeePEP 688 for more details.(Contributed by Shantanu Jain ingh-91896.)

Pending removal in Python 3.19¶

• ctypes:

  • Implicitly switching to the MSVC-compatible struct layout by setting_pack_ but not_layout_on non-Windows platforms.

• hashlib:

  • In hash function constructors such asnew() or thedirect hash-named constructors such asmd5() andsha256(), their optional initial data parameter couldalso be passed a keyword argument nameddata= orstring= invarioushashlib implementations.

    Support for thestring keyword argument name is now deprecatedand slated for removal in Python 3.19.

    Before Python 3.13, thestring keyword parameter was not correctlysupported depending on the backend implementation of hash functions.Prefer passing the initial data as a positional argument for maximumbackwards compatibility.

Pending removal in Python 3.20¶

• The__version__ attribute has been deprecated in these standard librarymodules and will be removed in Python 3.20.Usesys.version_info instead.

  • argparse

  • csv

  • ctypes.macholib

  • ipaddress

  • json

  • logging (__date__ also deprecated)

  • optparse

  • pickle

  • platform

  • re

  • socketserver

  • tabnanny

  • tkinter.font

  • tkinter.ttk

  (Contributed by Hugo van Kemenade ingh-76007.)

Pending removal in future versions¶

The following APIs will be removed in the future,although there is currently no date scheduled for their removal.

• argparse:

  • Nesting argument groups and nesting mutually exclusivegroups are deprecated.

  • Passing the undocumented keyword argumentprefix_chars toadd_argument_group() is nowdeprecated.

  • Theargparse.FileType type converter is deprecated.

• builtins:

  • Generators:throw(type,exc,tb) andathrow(type,exc,tb)signature is deprecated: usethrow(exc) andathrow(exc) instead,the single argument signature.

  • Currently Python accepts numeric literals immediately followed by keywords,for example0inx,1orx,0if1else2. It allows confusing andambiguous expressions like[0x1forxiny] (which can be interpreted as[0x1forxiny] or[0x1forxiny]). A syntax warning is raisedif the numeric literal is immediately followed by one of keywordsand,else,for,if,in,is andor. In a future release itwill be changed to a syntax error. (gh-87999)

  • Support for__index__() and__int__() method returning non-int type:these methods will be required to return an instance of a strict subclass ofint.

  • Support for__float__() method returning a strict subclass offloat: these methods will be required to return an instance offloat.

  • Support for__complex__() method returning a strict subclass ofcomplex: these methods will be required to return an instance ofcomplex.

  • Delegation ofint() to__trunc__() method.

  • Passing a complex number as thereal orimag argument in thecomplex() constructor is now deprecated; it should only be passedas a single positional argument.(Contributed by Serhiy Storchaka ingh-109218.)

• calendar:calendar.January andcalendar.February constants aredeprecated and replaced bycalendar.JANUARY andcalendar.FEBRUARY.(Contributed by Prince Roshan ingh-103636.)

• codecs: useopen() instead ofcodecs.open(). (gh-133038)

• codeobject.co_lnotab: use thecodeobject.co_lines() methodinstead.

• datetime:

  • utcnow():usedatetime.datetime.now(tz=datetime.UTC).

  • utcfromtimestamp():usedatetime.datetime.fromtimestamp(timestamp,tz=datetime.UTC).

• gettext: Plural value must be an integer.

• importlib:

  • cache_from_source()debug_override parameter isdeprecated: use theoptimization parameter instead.

• importlib.metadata:

  • EntryPoints tuple interface.

  • ImplicitNone on return values.

• logging: thewarn() method has been deprecatedsince Python 3.3, usewarning() instead.

• mailbox: Use of StringIO input and text mode is deprecated, useBytesIO and binary mode instead.

• os: Callingos.register_at_fork() in multi-threaded process.

• pydoc.ErrorDuringImport: A tuple value forexc_info parameter isdeprecated, use an exception instance.

• re: More strict rules are now applied for numerical group referencesand group names in regular expressions. Only sequence of ASCII digits is nowaccepted as a numerical reference. The group name in bytes patterns andreplacement strings can now only contain ASCII letters and digits andunderscore.(Contributed by Serhiy Storchaka ingh-91760.)

• shutil:rmtree()’sonerror parameter is deprecated inPython 3.12; use theonexc parameter instead.

• ssl options and protocols:

  • ssl.SSLContext without protocol argument is deprecated.

  • ssl.SSLContext:set_npn_protocols() andselected_npn_protocol() are deprecated: use ALPNinstead.

  • ssl.OP_NO_SSL* options

  • ssl.OP_NO_TLS* options

  • ssl.PROTOCOL_SSLv3

  • ssl.PROTOCOL_TLS

  • ssl.PROTOCOL_TLSv1

  • ssl.PROTOCOL_TLSv1_1

  • ssl.PROTOCOL_TLSv1_2

  • ssl.TLSVersion.SSLv3

  • ssl.TLSVersion.TLSv1

  • ssl.TLSVersion.TLSv1_1

• threading methods:

  • threading.Condition.notifyAll(): usenotify_all().

  • threading.Event.isSet(): useis_set().

  • threading.Thread.isDaemon(),threading.Thread.setDaemon():usethreading.Thread.daemon attribute.

  • threading.Thread.getName(),threading.Thread.setName():usethreading.Thread.name attribute.

  • threading.currentThread(): usethreading.current_thread().

  • threading.activeCount(): usethreading.active_count().

• typing.Text (gh-92332).

• The internal classtyping._UnionGenericAlias is no longer used to implementtyping.Union. To preserve compatibility with users using this privateclass, a compatibility shim will be provided until at least Python 3.17. (Contributed byJelle Zijlstra ingh-105499.)

• unittest.IsolatedAsyncioTestCase: it is deprecated to return a valuethat is notNone from a test case.

• urllib.parse deprecated functions:urlparse() instead

  • splitattr()

  • splithost()

  • splitnport()

  • splitpasswd()

  • splitport()

  • splitquery()

  • splittag()

  • splittype()

  • splituser()

  • splitvalue()

  • to_bytes()

• wsgiref:SimpleHandler.stdout.write() should not do partialwrites.

• xml.etree.ElementTree: Testing the truth value of anElement is deprecated. In a future release itwill always returnTrue. Prefer explicitlen(elem) orelemisnotNone tests instead.

• sys._clear_type_cache() is deprecated:usesys._clear_internal_caches() instead.

Pseudo-instructions¶

• Add theANNOTATIONS_PLACEHOLDER pseudo instructionto support partially executed module-level annotations withdeferred evaluation of annotations.(Contributed by Jelle Zijlstra ingh-130907.)

• Add theBINARY_OP_EXTEND pseudo instruction,which executes a pair of functions (guard and specialization functions)accessed from the inline cache.(Contributed by Irit Katriel ingh-100239.)

• Add three specializations forCALL_KW;CALL_KW_PY for calls to Python functions,CALL_KW_BOUND_METHOD for calls to bound methods, andCALL_KW_NON_PY for all other calls.(Contributed by Mark Shannon ingh-118093.)

• Add theJUMP_IF_TRUE andJUMP_IF_FALSE pseudo instructions,conditional jumps which do not impact the stack.Replaced by the sequenceCOPY1,TO_BOOL,POP_JUMP_IF_TRUE/FALSE.(Contributed by Irit Katriel ingh-124285.)

• Add theLOAD_CONST_MORTAL pseudo instruction.(Contributed by Mark Shannon ingh-128685.)

• Add theLOAD_CONST_IMMORTAL pseudo instruction,which does the same asLOAD_CONST, but is more efficientfor immortal objects.(Contributed by Mark Shannon ingh-125837.)

• Add theNOT_TAKEN pseudo instruction, used bysys.monitoringto record branch events (such asBRANCH_LEFT).(Contributed by Mark Shannon ingh-122548.)

Python configuration C API¶

Add aPyInitConfig C API to configure the Pythoninitialization without relying on C structures and the ability to makeABI-compatible changes in the future.

Complete thePEP 587PyConfig C API by addingPyInitConfig_AddModule() which can be used to add a built-in extensionmodule; a feature previously referred to as the “inittab”.

AddPyConfig_Get() andPyConfig_Set() functions to get and setthe current runtime configuration.

PEP 587 ‘Python Initialization Configuration’ unified all the waysto configure Python’s initialization. This PEP also unifies the configurationof Python’s preinitialization and initialization in a single API.Moreover, this PEP only provides a single choice to embed Python,instead of having two ‘Python’ and ‘Isolated’ choices (PEP 587),to further simplify the API.

The lower level PEP 587 PyConfig API remains available for use caseswith an intentionally higher level of coupling to CPython implementation details(such as emulating the full functionality of CPython’s CLI, including itsconfiguration mechanisms).

(Contributed by Victor Stinner ingh-107954.)

New features in the C API¶

• AddPy_PACK_VERSION() andPy_PACK_FULL_VERSION(),two new macros for bit-packing Python version numbers.This is useful for comparisons withPy_VersionorPY_VERSION_HEX.(Contributed by Petr Viktorin ingh-128629.)

• AddPyBytes_Join(sep,iterable) function,similar tosep.join(iterable) in Python.(Contributed by Victor Stinner ingh-121645.)

• Add functions to manipulate the configuration of the currentruntime Python interpreter(PEP 741: Python configuration C API):

  • PyConfig_Get()

  • PyConfig_GetInt()

  • PyConfig_Set()

  • PyConfig_Names()

  (Contributed by Victor Stinner ingh-107954.)

• Add functions to configure Python initialization(PEP 741: Python configuration C API):

  • Py_InitializeFromInitConfig()

  • PyInitConfig_AddModule()

  • PyInitConfig_Create()

  • PyInitConfig_Free()

  • PyInitConfig_FreeStrList()

  • PyInitConfig_GetError()

  • PyInitConfig_GetExitCode()

  • PyInitConfig_GetInt()

  • PyInitConfig_GetStr()

  • PyInitConfig_GetStrList()

  • PyInitConfig_HasOption()

  • PyInitConfig_SetInt()

  • PyInitConfig_SetStr()

  • PyInitConfig_SetStrList()

  (Contributed by Victor Stinner ingh-107954.)

• AddPy_fopen() function to open a file.This works similarly to the standard Cfopen() function,instead accepting a Python object for thepath parameterand setting an exception on error.The corresponding newPy_fclose() function should be usedto close a file.(Contributed by Victor Stinner ingh-127350.)

• AddPy_HashBuffer() to compute and return the hash value of a buffer.(Contributed by Antoine Pitrou and Victor Stinner ingh-122854.)

• AddPyImport_ImportModuleAttr() andPyImport_ImportModuleAttrString() helper functions to import a moduleand get an attribute of the module.(Contributed by Victor Stinner ingh-128911.)

• AddPyIter_NextItem() to replacePyIter_Next(),which has an ambiguous return value.(Contributed by Irit Katriel and Erlend Aasland ingh-105201.)

• AddPyLong_GetSign() function to get the sign ofint objects.(Contributed by Sergey B Kirpichev ingh-116560.)

• AddPyLong_IsPositive(),PyLong_IsNegative()andPyLong_IsZero() for checking ifPyLongObjectis positive, negative, or zero, respectively.(Contributed by James Roy and Sergey B Kirpichev ingh-126061.)

• Add new functions to convert C<stdint.h> numbers to/fromPythonint objects:

  • PyLong_AsInt32()

  • PyLong_AsInt64()

  • PyLong_AsUInt32()

  • PyLong_AsUInt64()

  • PyLong_FromInt32()

  • PyLong_FromInt64()

  • PyLong_FromUInt32()

  • PyLong_FromUInt64()

  (Contributed by Victor Stinner ingh-120389.)

• Add a new import and export API for Pythonint objects(PEP 757):

  • PyLong_GetNativeLayout()

  • PyLong_Export()

  • PyLong_FreeExport()

  • PyLongWriter_Create()

  • PyLongWriter_Finish()

  • PyLongWriter_Discard()

  (Contributed by Sergey B Kirpichev and Victor Stinner ingh-102471.)

• AddPyMonitoring_FireBranchLeftEvent() andPyMonitoring_FireBranchRightEvent() for generatingBRANCH_LEFT andBRANCH_RIGHTevents, respectively.(Contributed by Mark Shannon ingh-122548.)

• AddPyType_Freeze() function to make a type immutable.(Contributed by Victor Stinner ingh-121654.)

• AddPyType_GetBaseByToken() andPy_tp_token slotfor easier superclass identification, which attempts to resolve thetype checking issue mentioned inPEP 630.(Contributed ingh-124153.)

• Add a newPyUnicode_Equal() function to test if twostrings are equal.The function is also added to the Limited C API.(Contributed by Victor Stinner ingh-124502.)

• Add a newPyUnicodeWriter API to create a Pythonstrobject, with the following functions:

  • PyUnicodeWriter_Create()

  • PyUnicodeWriter_DecodeUTF8Stateful()

  • PyUnicodeWriter_Discard()

  • PyUnicodeWriter_Finish()

  • PyUnicodeWriter_Format()

  • PyUnicodeWriter_WriteASCII()

  • PyUnicodeWriter_WriteChar()

  • PyUnicodeWriter_WriteRepr()

  • PyUnicodeWriter_WriteStr()

  • PyUnicodeWriter_WriteSubstring()

  • PyUnicodeWriter_WriteUCS4()

  • PyUnicodeWriter_WriteUTF8()

  • PyUnicodeWriter_WriteWideChar()

  (Contributed by Victor Stinner ingh-119182.)

• Thek andK formats inPyArg_ParseTuple() andsimilar functions now use__index__() if available,like all other integer formats.(Contributed by Serhiy Storchaka ingh-112068.)

• Add support for a newp format unit inPy_BuildValue()that produces a Pythonbool object from a C integer.(Contributed by Pablo Galindo inbpo-45325.)

• AddPyUnstable_IsImmortal() for determining ifan object isimmortal, for debugging purposes.(Contributed by Peter Bierma ingh-128509.)

• AddPyUnstable_Object_EnableDeferredRefcount() for enablingdeferred reference counting, as outlined inPEP 703.

• AddPyUnstable_Object_IsUniquelyReferenced() asa replacement forPy_REFCNT(op)==1 onfree threaded builds.(Contributed by Peter Bierma ingh-133140.)

• AddPyUnstable_Object_IsUniqueReferencedTemporary() todetermine if an object is a unique temporary object on theinterpreter’s operand stack.This can be used in some cases as a replacement for checkingifPy_REFCNT() is1 for Python objects passedas arguments to C API functions.(Contributed by Sam Gross ingh-133164.)

Limited C API changes¶

• In the limited C API version 3.14 and newer,Py_TYPE() andPy_REFCNT() are now implemented as an opaque function callto hide implementation details.(Contributed by Victor Stinner ingh-120600 andgh-124127.)

• Remove thePySequence_Fast_GET_SIZE,PySequence_Fast_GET_ITEM,andPySequence_Fast_ITEMSmacros from the limited C API, since they have always been brokenin the limited C API.(Contributed by Victor Stinner ingh-91417.)

Removed C APIs¶

• Creatingimmutabletypes withmutable bases was deprecated in Python 3.12,and now raises aTypeError.(Contributed by Nikita Sobolev ingh-119775.)

• RemovePyDictObject.ma_version_tag member, which was deprecatedin Python 3.12.Use thePyDict_AddWatcher() API instead.(Contributed by Sam Gross ingh-124296.)

• Remove the private_Py_InitializeMain() function.It was aprovisional API added to Python 3.8 byPEP 587.(Contributed by Victor Stinner ingh-129033.)

• Remove the undocumented APIsPy_C_RECURSION_LIMITandPyThreadState.c_recursion_remaining.These were added in 3.13 and have been removed without deprecation.UsePy_EnterRecursiveCall() to guard against runawayrecursion in C code.(Removed by Petr Viktorin ingh-133079, see alsogh-130396.)

Deprecated C APIs¶

• ThePy_HUGE_VAL macro is nowsoft deprecated.UsePy_INFINITY instead.(Contributed by Sergey B Kirpichev ingh-120026.)

• ThePy_IS_NAN,Py_IS_INFINITY,andPy_IS_FINITE macros are nowsoft deprecated.Useisnan,isinf andisfiniteinstead, available frommath.h since C99.(Contributed by Sergey B Kirpichev ingh-119613.)

• Non-tuple sequences are now deprecated as argument for the(items)format unit inPyArg_ParseTuple() and otherargumentparsing functions ifitems contains format unitswhich store aborrowed buffer or aborrowed reference.(Contributed by Serhiy Storchaka ingh-50333.)

• The_PyMonitoring_FireBranchEvent function is now deprecatedand should be replaced with calls toPyMonitoring_FireBranchLeftEvent() andPyMonitoring_FireBranchRightEvent().

• The previously undocumented functionPySequence_In() isnowsoft deprecated.UsePySequence_Contains() instead.(Contributed by Yuki Kobayashi ingh-127896.)