Assignment expressions¶

There is new syntax:= that assigns values to variables as part of a largerexpression. It is affectionately known as “the walrus operator” due toits resemblance tothe eyes and tusks of a walrus.

In this example, the assignment expression helps avoid callinglen() twice:

if(n:=len(a))>10:print(f"List is too long ({n} elements, expected <= 10)")

A similar benefit arises during regular expression matching wherematch objects are needed twice, once to test whether a matchoccurred and another to extract a subgroup:

discount=0.0if(mo:=re.search(r'(\d+)% discount',advertisement)):discount=float(mo.group(1))/100.0

The operator is also useful with while-loops that computea value to test loop termination and then need that samevalue again in the body of the loop:

# Loop over fixed length blockswhile(block:=f.read(256))!='':process(block)

Another motivating use case arises in list comprehensions wherea value computed in a filtering condition is also needed inthe expression body:

[clean_name.title()fornameinnamesif(clean_name:=normalize('NFC',name))inallowed_names]

Try to limit use of the walrus operator to clean cases that reducecomplexity and improve readability.

SeePEP 572 for a full description.

(Contributed by Emily Morehouse inbpo-35224.)

Positional-only parameters¶

There is a new function parameter syntax/ to indicate that somefunction parameters must be specified positionally and cannot be used askeyword arguments. This is the same notation shown byhelp() for Cfunctions annotated with Larry Hastings’Argument Clinic tool.

In the following example, parametersa andb are positional-only,whilec ord can be positional or keyword, ande orf arerequired to be keywords:

deff(a,b,/,c,d,*,e,f):print(a,b,c,d,e,f)

The following is a valid call:

f(10,20,30,d=40,e=50,f=60)

However, these are invalid calls:

f(10,b=20,c=30,d=40,e=50,f=60)# b cannot be a keyword argumentf(10,20,30,40,50,f=60)# e must be a keyword argument

One use case for this notation is that it allows pure Python functionsto fully emulate behaviors of existing C coded functions. For example,the built-indivmod() function does not accept keyword arguments:

defdivmod(a,b,/):"Emulate the built in divmod() function"return(a//b,a%b)

Another use case is to preclude keyword arguments when the parametername is not helpful. For example, the builtinlen() function hasthe signaturelen(obj,/). This precludes awkward calls such as:

len(obj='hello')# The "obj" keyword argument impairs readability

A further benefit of marking a parameter as positional-only is that itallows the parameter name to be changed in the future without risk ofbreaking client code. For example, in thestatistics module, theparameter namedist may be changed in the future. This was madepossible with the following function specification:

defquantiles(dist,/,*,n=4,method='exclusive')...

Since the parameters to the left of/ are not exposed as possiblekeywords, the parameters names remain available for use in**kwargs:

>>>deff(a,b,/,**kwargs):...print(a,b,kwargs)...>>>f(10,20,a=1,b=2,c=3)# a and b are used in two ways10 20 {'a': 1, 'b': 2, 'c': 3}

This greatly simplifies the implementation of functions and methodsthat need to accept arbitrary keyword arguments. For example, hereis an excerpt from code in thecollections module:

classCounter(dict):def__init__(self,iterable=None,/,**kwds):# Note "iterable" is a possible keyword argument

SeePEP 570 for a full description.

(Contributed by Pablo Galindo inbpo-36540.)

Parallel filesystem cache for compiled bytecode files¶

The newPYTHONPYCACHEPREFIX setting (also available as-Xpycache_prefix) configures the implicit bytecodecache to use a separate parallel filesystem tree, rather thanthe default__pycache__ subdirectories within each sourcedirectory.

The location of the cache is reported insys.pycache_prefix(None indicates the default location in__pycache__subdirectories).

(Contributed by Carl Meyer inbpo-33499.)

Debug build uses the same ABI as release build¶

Python now uses the same ABI whether it’s built in release or debug mode. OnUnix, when Python is built in debug mode, it is now possible to load Cextensions built in release mode and C extensions built using the stable ABI.

Release builds and debug builds are now ABI compatible: defining thePy_DEBUG macro no longer implies thePy_TRACE_REFS macro, whichintroduces the only ABI incompatibility. ThePy_TRACE_REFS macro, whichadds thesys.getobjects() function and thePYTHONDUMPREFSenvironment variable, can be set using the new./configure--with-trace-refsbuild option.(Contributed by Victor Stinner inbpo-36465.)

On Unix, C extensions are no longer linked to libpython except on Androidand Cygwin.It is now possiblefor a statically linked Python to load a C extension built using a sharedlibrary Python.(Contributed by Victor Stinner inbpo-21536.)

On Unix, when Python is built in debug mode, import now also looks for Cextensions compiled in release mode and for C extensions compiled with thestable ABI.(Contributed by Victor Stinner inbpo-36722.)

To embed Python into an application, a new--embed option must be passed topython3-config--libs--embed to get-lpython3.8 (link the applicationto libpython). To support both 3.8 and older, trypython3-config--libs--embed first and fallback topython3-config--libs (without--embed)if the previous command fails.

Add a pkg-configpython-3.8-embed module to embed Python into anapplication:pkg-configpython-3.8-embed--libs includes-lpython3.8.To support both 3.8 and older, trypkg-configpython-X.Y-embed--libs firstand fallback topkg-configpython-X.Y--libs (without--embed) if theprevious command fails (replaceX.Y with the Python version).

On the other hand,pkg-configpython3.8--libs no longer contains-lpython3.8. C extensions must not be linked to libpython (except onAndroid and Cygwin, whose cases are handled by the script);this change is backward incompatible on purpose.(Contributed by Victor Stinner inbpo-36721.)

f-strings support= for self-documenting expressions and debugging¶

Added an= specifier tof-strings. An f-string such asf'{expr=}' will expand to the text of the expression, an equal sign,then the representation of the evaluated expression. For example:

>>>user='eric_idle'>>>member_since=date(1975,7,31)>>>f'{user=}{member_since=}'"user='eric_idle' member_since=datetime.date(1975, 7, 31)"

The usualf-string format specifiers allow morecontrol over how the result of the expression is displayed:

>>>delta=date.today()-member_since>>>f'{user=!s}{delta.days=:,d}''user=eric_idle  delta.days=16,075'

The= specifier will display the whole expression so thatcalculations can be shown:

>>>print(f'{theta=}{cos(radians(theta))=:.3f}')theta=30  cos(radians(theta))=0.866

(Contributed by Eric V. Smith and Larry Hastings inbpo-36817.)

PEP 578: Python Runtime Audit Hooks¶

The PEP adds an Audit Hook and Verified Open Hook. Both are available fromPython and native code, allowing applications and frameworks written in purePython code to take advantage of extra notifications, while also allowingembedders or system administrators to deploy builds of Python where auditing isalways enabled.

SeePEP 578 for full details.

PEP 587: Python Initialization Configuration¶

ThePEP 587 adds a new C API to configure the Python Initializationproviding finer control on the whole configuration and better error reporting.

New structures:

• PyConfig

• PyPreConfig

• PyStatus

• PyWideStringList

New functions:

• PyConfig_Clear()

• PyConfig_InitIsolatedConfig()

• PyConfig_InitPythonConfig()

• PyConfig_Read()

• PyConfig_SetArgv()

• PyConfig_SetBytesArgv()

• PyConfig_SetBytesString()

• PyConfig_SetString()

• PyPreConfig_InitIsolatedConfig()

• PyPreConfig_InitPythonConfig()

• PyStatus_Error()

• PyStatus_Exception()

• PyStatus_Exit()

• PyStatus_IsError()

• PyStatus_IsExit()

• PyStatus_NoMemory()

• PyStatus_Ok()

• PyWideStringList_Append()

• PyWideStringList_Insert()

• Py_BytesMain()

• Py_ExitStatusException()

• Py_InitializeFromConfig()

• Py_PreInitialize()

• Py_PreInitializeFromArgs()

• Py_PreInitializeFromBytesArgs()

• Py_RunMain()

This PEP also adds_PyRuntimeState.preconfig (PyPreConfig type)andPyInterpreterState.config (PyConfig type) fields to theseinternal structures.PyInterpreterState.config becomes the newreference configuration, replacing global configuration variables andother private variables.

SeePython Initialization Configuration for thedocumentation.

SeePEP 587 for a full description.

(Contributed by Victor Stinner inbpo-36763.)

PEP 590: Vectorcall: a fast calling protocol for CPython¶

The Vectorcall Protocol is added to the Python/C API.It is meant to formalize existing optimizations which were already donefor various classes.Any static type implementing a callable can use this protocol.

This is currently provisional.The aim is to make it fully public in Python 3.9.

SeePEP 590 for a full description.

(Contributed by Jeroen Demeyer, Mark Shannon and Petr Viktorin inbpo-36974.)

Pickle protocol 5 with out-of-band data buffers¶

Whenpickle is used to transfer large data between Python processesin order to take advantage of multi-core or multi-machine processing,it is important to optimize the transfer by reducing memory copies, andpossibly by applying custom techniques such as data-dependent compression.

Thepickle protocol 5 introduces support for out-of-band bufferswherePEP 3118-compatible data can be transmitted separately from themain pickle stream, at the discretion of the communication layer.

SeePEP 574 for a full description.

(Contributed by Antoine Pitrou inbpo-36785.)

ast¶

AST nodes now haveend_lineno andend_col_offset attributes,which give the precise location of the end of the node. (This onlyapplies to nodes that havelineno andcol_offset attributes.)

New functionast.get_source_segment() returns the source codefor a specific AST node.

(Contributed by Ivan Levkivskyi inbpo-33416.)

Theast.parse() function has some new flags:

• type_comments=True causes it to return the text ofPEP 484 andPEP 526 type comments associated with certain AST nodes;

• mode='func_type' can be used to parsePEP 484 “signature typecomments” (returned for function definition AST nodes);

• feature_version=(3,N) allows specifying an earlier Python 3version. For example,feature_version=(3,4) will treatasync andawait as non-reserved words.

(Contributed by Guido van Rossum inbpo-35766.)

asyncio¶

asyncio.run() has graduated from the provisional to stable API. Thisfunction can be used to execute acoroutine and return the result whileautomatically managing the event loop. For example:

importasyncioasyncdefmain():awaitasyncio.sleep(0)return42asyncio.run(main())

This isroughly equivalent to:

importasyncioasyncdefmain():awaitasyncio.sleep(0)return42loop=asyncio.new_event_loop()asyncio.set_event_loop(loop)try:loop.run_until_complete(main())finally:asyncio.set_event_loop(None)loop.close()

The actual implementation is significantly more complex. Thus,asyncio.run() should be the preferred way of running asyncio programs.

(Contributed by Yury Selivanov inbpo-32314.)

Runningpython-masyncio launches a natively async REPL. This allows rapidexperimentation with code that has a top-levelawait. There is nolonger a need to directly callasyncio.run() which would spawn a new eventloop on every invocation:

$ python -m asyncioasyncio REPL 3.8.0Use "await" directly instead of "asyncio.run()".Type "help", "copyright", "credits" or "license" for more information.>>> import asyncio>>> await asyncio.sleep(10, result='hello')hello

(Contributed by Yury Selivanov inbpo-37028.)

The exceptionasyncio.CancelledError now inherits fromBaseException rather thanException and no longer inheritsfromconcurrent.futures.CancelledError.(Contributed by Yury Selivanov inbpo-32528.)

On Windows, the default event loop is nowProactorEventLoop.(Contributed by Victor Stinner inbpo-34687.)

ProactorEventLoop now also supports UDP.(Contributed by Adam Meily and Andrew Svetlov inbpo-29883.)

ProactorEventLoop can now be interrupted byKeyboardInterrupt (“CTRL+C”).(Contributed by Vladimir Matveev inbpo-23057.)

Addedasyncio.Task.get_coro() for getting the wrapped coroutinewithin anasyncio.Task.(Contributed by Alex Grönholm inbpo-36999.)

Asyncio tasks can now be named, either by passing thename keywordargument toasyncio.create_task() orthecreate_task() event loop method, or bycalling theset_name() method on the task object. Thetask name is visible in therepr() output ofasyncio.Task andcan also be retrieved using theget_name() method.(Contributed by Alex Grönholm inbpo-34270.)

Added support forHappy Eyeballs toasyncio.loop.create_connection(). To specify the behavior, two newparameters have been added:happy_eyeballs_delay andinterleave. The HappyEyeballs algorithm improves responsiveness in applications that support IPv4and IPv6 by attempting to simultaneously connect using both.(Contributed by twisteroid ambassador inbpo-33530.)

builtins¶

Thecompile() built-in has been improved to accept theast.PyCF_ALLOW_TOP_LEVEL_AWAIT flag. With this new flag passed,compile() will allow top-levelawait,asyncfor andasyncwithconstructs that are usually considered invalid syntax. Asynchronous code objectmarked with theCO_COROUTINE flag may then be returned.(Contributed by Matthias Bussonnier inbpo-34616)

collections¶

The_asdict() method forcollections.namedtuple() now returns adict instead of acollections.OrderedDict. This works because regular dicts haveguaranteed ordering since Python 3.7. If the extra features ofOrderedDict are required, the suggested remediation is to cast theresult to the desired type:OrderedDict(nt._asdict()).(Contributed by Raymond Hettinger inbpo-35864.)

cProfile¶

ThecProfile.Profile class can now be used as a context manager.Profile a block of code by running:

importcProfilewithcProfile.Profile()asprofiler:# code to be profiled...

(Contributed by Scott Sanderson inbpo-29235.)

csv¶

Thecsv.DictReader now returns instances ofdict instead ofacollections.OrderedDict. The tool is now faster and uses lessmemory while still preserving the field order.(Contributed by Michael Selik inbpo-34003.)

curses¶

Added a new variable holding structured version information for theunderlying ncurses library:ncurses_version.(Contributed by Serhiy Storchaka inbpo-31680.)

ctypes¶

On Windows,CDLL and subclasses now accept awinmode parameterto specify flags for the underlyingLoadLibraryEx call. The default flags areset to only load DLL dependencies from trusted locations, including the pathwhere the DLL is stored (if a full or partial path is used to load the initialDLL) and paths added byadd_dll_directory().(Contributed by Steve Dower inbpo-36085.)

datetime¶

Added new alternate constructorsdatetime.date.fromisocalendar() anddatetime.datetime.fromisocalendar(), which constructdate anddatetime objects respectively from ISO year, week number, and weekday;these are the inverse of each class’sisocalendar method.(Contributed by Paul Ganssle inbpo-36004.)

functools¶

functools.lru_cache() can now be used as a straight decorator ratherthan as a function returning a decorator. So both of these are now supported:

@lru_cachedeff(x):...@lru_cache(maxsize=256)deff(x):...

(Contributed by Raymond Hettinger inbpo-36772.)

Added a newfunctools.cached_property() decorator, for computed propertiescached for the life of the instance.

importfunctoolsimportstatisticsclassDataset:def__init__(self,sequence_of_numbers):self.data=sequence_of_numbers@functools.cached_propertydefvariance(self):returnstatistics.variance(self.data)

(Contributed by Carl Meyer inbpo-21145)

Added a newfunctools.singledispatchmethod() decorator that convertsmethods intogeneric functions usingsingle dispatch:

fromfunctoolsimportsingledispatchmethodfromcontextlibimportsuppressclassTaskManager:def__init__(self,tasks):self.tasks=list(tasks)@singledispatchmethoddefdiscard(self,value):withsuppress(ValueError):self.tasks.remove(value)@discard.register(list)def_(self,tasks):targets=set(tasks)self.tasks=[xforxinself.tasksifxnotintargets]

(Contributed by Ethan Smith inbpo-32380)

gc¶

get_objects() can now receive an optionalgeneration parameterindicating a generation to get objects from.(Contributed by Pablo Galindo inbpo-36016.)

gettext¶

Addedpgettext() and its variants.(Contributed by Franz Glasner, Éric Araujo, and Cheryl Sabella inbpo-2504.)

gzip¶

Added themtime parameter togzip.compress() for reproducible output.(Contributed by Guo Ci Teo inbpo-34898.)

ABadGzipFile exception is now raised instead ofOSErrorfor certain types of invalid or corrupt gzip files.(Contributed by Filip Gruszczyński, Michele Orrù, and Zackery Spytz inbpo-6584.)

IDLE and idlelib¶

Output over N lines (50 by default) is squeezed down to a button.N can be changed in the PyShell section of the General page of theSettings dialog. Fewer, but possibly extra long, lines can be squeezed byright clicking on the output. Squeezed output can be expanded in placeby double-clicking the button or into the clipboard or a separate windowby right-clicking the button. (Contributed by Tal Einat inbpo-1529353.)

Add “Run Customized” to the Run menu to run a module with customizedsettings. Any command line arguments entered are added to sys.argv.They also re-appear in the box for the next customized run. One can alsosuppress the normal Shell main module restart. (Contributed by CherylSabella, Terry Jan Reedy, and others inbpo-5680 andbpo-37627.)

Added optional line numbers for IDLE editor windows. Windowsopen without line numbers unless set otherwise in the Generaltab of the configuration dialog. Line numbers for an existingwindow are shown and hidden in the Options menu.(Contributed by Tal Einat and Saimadhav Heblikar inbpo-17535.)

OS native encoding is now used for converting between Python strings and Tclobjects. This allows IDLE to work with emoji and other non-BMP characters.These characters can be displayed or copied and pasted to or from theclipboard. Converting strings from Tcl to Python and back now never fails.(Many people worked on this for eight years but the problem was finallysolved by Serhiy Storchaka inbpo-13153.)

New in 3.8.1:

Add option to toggle cursor blink off. (Contributed by Zackery Spytzinbpo-4603.)

Escape key now closes IDLE completion windows. (Contributed by JohnnyNajera inbpo-38944.)

The changes above have been backported to 3.7 maintenance releases.

Add keywords to module name completion list. (Contributed by Terry J.Reedy inbpo-37765.)

inspect¶

Theinspect.getdoc() function can now find docstrings for__slots__if that attribute is adict where the values are docstrings.This provides documentation options similar to what we already haveforproperty(),classmethod(), andstaticmethod():

classAudioClip:__slots__={'bit_rate':'expressed in kilohertz to one decimal place','duration':'in seconds, rounded up to an integer'}def__init__(self,bit_rate,duration):self.bit_rate=round(bit_rate/1000.0,1)self.duration=ceil(duration)

(Contributed by Raymond Hettinger inbpo-36326.)

io¶

In development mode (-Xenv) and in debug build, theio.IOBase finalizer now logs the exception if theclose() methodfails. The exception is ignored silently by default in release build.(Contributed by Victor Stinner inbpo-18748.)

itertools¶

Theitertools.accumulate() function added an optioninitial keywordargument to specify an initial value:

>>>fromitertoolsimportaccumulate>>>list(accumulate([10,5,30,15],initial=1000))[1000, 1010, 1015, 1045, 1060]

(Contributed by Lisa Roach inbpo-34659.)

json.tool¶

Add option--json-lines to parse every input line as a separate JSON object.(Contributed by Weipeng Hong inbpo-31553.)

logging¶

Added aforce keyword argument tologging.basicConfig()When set to true, any existing handlers attachedto the root logger are removed and closed before carrying out theconfiguration specified by the other arguments.

This solves a long-standing problem. Once a logger orbasicConfig() hadbeen called, subsequent calls tobasicConfig() were silently ignored.This made it difficult to update, experiment with, or teach the variouslogging configuration options using the interactive prompt or a Jupyternotebook.

(Suggested by Raymond Hettinger, implemented by Dong-hee Na, andreviewed by Vinay Sajip inbpo-33897.)

math¶

Added new functionmath.dist() for computing Euclidean distancebetween two points. (Contributed by Raymond Hettinger inbpo-33089.)

Expanded themath.hypot() function to handle multiple dimensions.Formerly, it only supported the 2-D case.(Contributed by Raymond Hettinger inbpo-33089.)

Added new function,math.prod(), as analogous function tosum()that returns the product of a ‘start’ value (default: 1) times an iterable ofnumbers:

>>>prior=0.8>>>likelihoods=[0.625,0.84,0.30]>>>math.prod(likelihoods,start=prior)0.126

(Contributed by Pablo Galindo inbpo-35606.)

Added two new combinatoric functionsmath.perm() andmath.comb():

>>>math.perm(10,3)# Permutations of 10 things taken 3 at a time720>>>math.comb(10,3)# Combinations of 10 things taken 3 at a time120

(Contributed by Yash Aggarwal, Keller Fuchs, Serhiy Storchaka, and RaymondHettinger inbpo-37128,bpo-37178, andbpo-35431.)

Added a new functionmath.isqrt() for computing accurate integer squareroots without conversion to floating point. The new function supportsarbitrarily large integers. It is faster thanfloor(sqrt(n)) but slowerthanmath.sqrt():

>>>r=650320427>>>s=r**2>>>isqrt(s-1)# correct650320426>>>floor(sqrt(s-1))# incorrect650320427

(Contributed by Mark Dickinson inbpo-36887.)

The functionmath.factorial() no longer accepts arguments that are notint-like. (Contributed by Pablo Galindo inbpo-33083.)

mmap¶

Themmap.mmap class now has anmadvise() method toaccess themadvise() system call.(Contributed by Zackery Spytz inbpo-32941.)

multiprocessing¶

Added newmultiprocessing.shared_memory module.(Contributed by Davin Potts inbpo-35813.)

On macOS, thespawn start method is now used by default.(Contributed by Victor Stinner inbpo-33725.)

os¶

Added new functionadd_dll_directory() on Windows for providingadditional search paths for native dependencies when importing extensionmodules or loading DLLs usingctypes.(Contributed by Steve Dower inbpo-36085.)

A newos.memfd_create() function was added to wrap thememfd_create() syscall.(Contributed by Zackery Spytz and Christian Heimes inbpo-26836.)

On Windows, much of the manual logic for handling reparse points (includingsymlinks and directory junctions) has been delegated to the operating system.Specifically,os.stat() will now traverse anything supported by theoperating system, whileos.lstat() will only open reparse points thatidentify as “name surrogates” while others are opened as foros.stat().In all cases,stat_result.st_mode will only haveS_IFLNK set forsymbolic links and not other kinds of reparse points. To identify other kindsof reparse point, check the newstat_result.st_reparse_tag attribute.

On Windows,os.readlink() is now able to read directory junctions. Notethatislink() will returnFalse for directory junctions,and so code that checksislink first will continue to treat junctions asdirectories, while code that handles errors fromos.readlink() may nowtreat junctions as links.

(Contributed by Steve Dower inbpo-37834.)

os.path¶

os.path functions that return a boolean result likeexists(),lexists(),isdir(),isfile(),islink(), andismount()now returnFalse instead of raisingValueError or its subclassesUnicodeEncodeError andUnicodeDecodeError for paths that containcharacters or bytes unrepresentable at the OS level.(Contributed by Serhiy Storchaka inbpo-33721.)

expanduser() on Windows now prefers theUSERPROFILEenvironment variable and does not useHOME, which is not normally setfor regular user accounts.(Contributed by Anthony Sottile inbpo-36264.)

isdir() on Windows no longer returnsTrue for a link to anon-existent directory.

realpath() on Windows now resolves reparse points, includingsymlinks and directory junctions.

(Contributed by Steve Dower inbpo-37834.)

pathlib¶

pathlib.Path methods that return a boolean result likeexists(),is_dir(),is_file(),is_mount(),is_symlink(),is_block_device(),is_char_device(),is_fifo(),is_socket() now returnFalse instead of raisingValueError or its subclassUnicodeEncodeError for paths thatcontain characters unrepresentable at the OS level.(Contributed by Serhiy Storchaka inbpo-33721.)

Addedpathlib.Path.link_to() which creates a hard link pointingto a path.(Contributed by Joannah Nanjekye inbpo-26978)

pickle¶

pickle extensions subclassing the C-optimizedPicklercan now override the pickling logic of functions and classes by defining thespecialreducer_override() method.(Contributed by Pierre Glaser and Olivier Grisel inbpo-35900.)

plistlib¶

Added newplistlib.UID and enabled support for reading and writingNSKeyedArchiver-encoded binary plists.(Contributed by Jon Janzen inbpo-26707.)

pprint¶

Thepprint module added asort_dicts parameter to several functions.By default, those functions continue to sort dictionaries before rendering orprinting. However, ifsort_dicts is set to false, the dictionaries retainthe order that keys were inserted. This can be useful for comparison to JSONinputs during debugging.

In addition, there is a convenience new function,pprint.pp() that islikepprint.pprint() but withsort_dicts defaulting toFalse:

>>>frompprintimportpprint,pp>>>d=dict(source='input.txt',operation='filter',destination='output.txt')>>>pp(d,width=40)# Original order{'source': 'input.txt', 'operation': 'filter', 'destination': 'output.txt'}>>>pprint(d,width=40)# Keys sorted alphabetically{'destination': 'output.txt', 'operation': 'filter', 'source': 'input.txt'}

(Contributed by Rémi Lapeyre inbpo-30670.)

py_compile¶

py_compile.compile() now supports silent mode.(Contributed by Joannah Nanjekye inbpo-22640.)

shlex¶

The newshlex.join() function acts as the inverse ofshlex.split().(Contributed by Bo Bayles inbpo-32102.)

shutil¶

shutil.copytree() now accepts a newdirs_exist_ok keyword argument.(Contributed by Josh Bronson inbpo-20849.)

shutil.make_archive() now defaults to the modern pax (POSIX.1-2001)format for new archives to improve portability and standards conformance,inherited from the corresponding change to thetarfile module.(Contributed by C.A.M. Gerlach inbpo-30661.)

shutil.rmtree() on Windows now removes directory junctions withoutrecursively removing their contents first.(Contributed by Steve Dower inbpo-37834.)

socket¶

Addedcreate_server() andhas_dualstack_ipv6()convenience functions to automate the necessary tasks usually involved whencreating a server socket, including accepting both IPv4 and IPv6 connectionson the same socket. (Contributed by Giampaolo Rodolà inbpo-17561.)

Thesocket.if_nameindex(),socket.if_nametoindex(), andsocket.if_indextoname() functions have been implemented on Windows.(Contributed by Zackery Spytz inbpo-37007.)

ssl¶

Addedpost_handshake_auth to enable andverify_client_post_handshake() to initiate TLS 1.3post-handshake authentication.(Contributed by Christian Heimes inbpo-34670.)

statistics¶

Addedstatistics.fmean() as a faster, floating point variant ofstatistics.mean(). (Contributed by Raymond Hettinger andSteven D’Aprano inbpo-35904.)

Addedstatistics.geometric_mean()(Contributed by Raymond Hettinger inbpo-27181.)

Addedstatistics.multimode() that returns a list of the mostcommon values. (Contributed by Raymond Hettinger inbpo-35892.)

Addedstatistics.quantiles() that divides data or a distributionin to equiprobable intervals (e.g. quartiles, deciles, or percentiles).(Contributed by Raymond Hettinger inbpo-36546.)

Addedstatistics.NormalDist, a tool for creatingand manipulating normal distributions of a random variable.(Contributed by Raymond Hettinger inbpo-36018.)

>>>temperature_feb=NormalDist.from_samples([4,12,-3,2,7,14])>>>temperature_feb.mean6.0>>>temperature_feb.stdev6.356099432828281>>>temperature_feb.cdf(3)# Chance of being under 3 degrees0.3184678262814532>>># Relative chance of being 7 degrees versus 10 degrees>>>temperature_feb.pdf(7)/temperature_feb.pdf(10)1.2039930378537762>>>el_niño=NormalDist(4,2.5)>>>temperature_feb+=el_niño# Add in a climate effect>>>temperature_febNormalDist(mu=10.0, sigma=6.830080526611674)>>>temperature_feb*(9/5)+32# Convert to FahrenheitNormalDist(mu=50.0, sigma=12.294144947901014)>>>temperature_feb.samples(3)# Generate random samples[7.672102882379219, 12.000027119750287, 4.647488369766392]

sys¶

Add newsys.unraisablehook() function which can be overridden to controlhow “unraisable exceptions” are handled. It is called when an exception hasoccurred but there is no way for Python to handle it. For example, when adestructor raises an exception or during garbage collection(gc.collect()).(Contributed by Victor Stinner inbpo-36829.)

tarfile¶

Thetarfile module now defaults to the modern pax (POSIX.1-2001)format for new archives, instead of the previous GNU-specific one.This improves cross-platform portability with a consistent encoding (UTF-8)in a standardized and extensible format, and offers several other benefits.(Contributed by C.A.M. Gerlach inbpo-36268.)

threading¶

Add a newthreading.excepthook() function which handles uncaughtthreading.Thread.run() exception. It can be overridden to control howuncaughtthreading.Thread.run() exceptions are handled.(Contributed by Victor Stinner inbpo-1230540.)

Add a newthreading.get_native_id() function andanative_idattribute to thethreading.Thread class. These return the nativeintegral Thread ID of the current thread assigned by the kernel.This feature is only available on certain platforms, seeget_native_id for more information.(Contributed by Jake Tesler inbpo-36084.)

tokenize¶

Thetokenize module now implicitly emits aNEWLINE token whenprovided with input that does not have a trailing new line. This behaviornow matches what the C tokenizer does internally.(Contributed by Ammar Askar inbpo-33899.)

tkinter¶

Added methodsselection_from(),selection_present(),selection_range() andselection_to()in thetkinter.Spinbox class.(Contributed by Juliette Monsel inbpo-34829.)

Added methodmoveto()in thetkinter.Canvas class.(Contributed by Juliette Monsel inbpo-23831.)

Thetkinter.PhotoImage class now hastransparency_get() andtransparency_set() methods. (Contributed byZackery Spytz inbpo-25451.)

time¶

Added new clockCLOCK_UPTIME_RAW for macOS 10.12.(Contributed by Joannah Nanjekye inbpo-35702.)

typing¶

Thetyping module incorporates several new features:

• A dictionary type with per-key types. SeePEP 589 andtyping.TypedDict.TypedDict uses only string keys. By default, every key is requiredto be present. Specify “total=False” to allow keys to be optional:

  classLocation(TypedDict,total=False):lat_long:tuplegrid_square:strxy_coordinate:tuple

• Literal types. SeePEP 586 andtyping.Literal.Literal types indicate that a parameter or return valueis constrained to one or more specific literal values:

  defget_status(port:int)->Literal['connected','disconnected']:...

• “Final” variables, functions, methods and classes. SeePEP 591,typing.Final andtyping.final().The final qualifier instructs a static type checker to restrictsubclassing, overriding, or reassignment:

  pi:Final[float]=3.1415926536

• Protocol definitions. SeePEP 544,typing.Protocol andtyping.runtime_checkable(). Simple ABCs liketyping.SupportsInt are nowProtocol subclasses.

• New protocol classtyping.SupportsIndex.

• New functionstyping.get_origin() andtyping.get_args().

unicodedata¶

Theunicodedata module has been upgraded to use theUnicode 12.1.0 release.

New functionis_normalized() can be used to verify a stringis in a specific normal form, often much faster than by actually normalizingthe string. (Contributed by Max Belanger, David Euresti, and Greg Price inbpo-32285 andbpo-37966).

unittest¶

AddedAsyncMock to support an asynchronous version ofMock. Appropriate new assert functions for testinghave been added as well.(Contributed by Lisa Roach inbpo-26467).

AddedaddModuleCleanup() andaddClassCleanup() to unittest to supportcleanups forsetUpModule() andsetUpClass().(Contributed by Lisa Roach inbpo-24412.)

Several mock assert functions now also print a list of actual calls uponfailure. (Contributed by Petter Strandmark inbpo-35047.)

unittest module gained support for coroutines to be used as test caseswithunittest.IsolatedAsyncioTestCase.(Contributed by Andrew Svetlov inbpo-32972.)

Example:

importunittestclassTestRequest(unittest.IsolatedAsyncioTestCase):asyncdefasyncSetUp(self):self.connection=awaitAsyncConnection()asyncdeftest_get(self):response=awaitself.connection.get("https://example.com")self.assertEqual(response.status_code,200)asyncdefasyncTearDown(self):awaitself.connection.close()if__name__=="__main__":unittest.main()

venv¶

venv now includes anActivate.ps1 script on all platforms foractivating virtual environments under PowerShell Core 6.1.(Contributed by Brett Cannon inbpo-32718.)

weakref¶

The proxy objects returned byweakref.proxy() now support the matrixmultiplication operators@ and@= in addition to the othernumeric operators. (Contributed by Mark Dickinson inbpo-36669.)

xml¶

As mitigation against DTD and external entity retrieval, thexml.dom.minidom andxml.sax modules no longer processexternal entities by default.(Contributed by Christian Heimes inbpo-17239.)

The.find*() methods in thexml.etree.ElementTree modulesupport wildcard searches like{*}tag which ignores the namespaceand{namespace}* which returns all tags in the given namespace.(Contributed by Stefan Behnel inbpo-28238.)

Thexml.etree.ElementTree module provides a new function–xml.etree.ElementTree.canonicalize() that implements C14N 2.0.(Contributed by Stefan Behnel inbpo-13611.)

The target object ofxml.etree.ElementTree.XMLParser canreceive namespace declaration events through the new callback methodsstart_ns() andend_ns(). Additionally, thexml.etree.ElementTree.TreeBuilder target can be configuredto process events about comments and processing instructions to includethem in the generated tree.(Contributed by Stefan Behnel inbpo-36676 andbpo-36673.)

xmlrpc¶

xmlrpc.client.ServerProxy now supports an optionalheaders keywordargument for a sequence of HTTP headers to be sent with each request. Amongother things, this makes it possible to upgrade from default basicauthentication to faster session authentication.(Contributed by Cédric Krier inbpo-35153.)

Changes in Python behavior¶

• Yield expressions (bothyield andyieldfrom clauses) are now disallowedin comprehensions and generator expressions (aside from the iterable expressionin the leftmostfor clause).(Contributed by Serhiy Storchaka inbpo-10544.)

• The compiler now produces aSyntaxWarning when identity checks(is andisnot) are used with certain types of literals(e.g. strings, numbers). These can often work by accident in CPython,but are not guaranteed by the language spec. The warning advises usersto use equality tests (== and!=) instead.(Contributed by Serhiy Storchaka inbpo-34850.)

• The CPython interpreter can swallow exceptions in some circumstances.In Python 3.8 this happens in fewer cases. In particular, exceptionsraised when getting the attribute from the type dictionary are no longerignored. (Contributed by Serhiy Storchaka inbpo-35459.)

• Removed__str__ implementations from builtin typesbool,int,float,complex and few classes fromthe standard library. They now inherit__str__() fromobject.As result, defining the__repr__() method in the subclass of theseclasses will affect their string representation.(Contributed by Serhiy Storchaka inbpo-36793.)

• On AIX,sys.platform doesn’t contain the major version anymore.It is always'aix', instead of'aix3' ..'aix7'. Sinceolder Python versions include the version number, so it is recommended toalways usesys.platform.startswith('aix').(Contributed by M. Felt inbpo-36588.)

• PyEval_AcquireLock() andPyEval_AcquireThread() nowterminate the current thread if called while the interpreter isfinalizing, making them consistent withPyEval_RestoreThread(),Py_END_ALLOW_THREADS(), andPyGILState_Ensure(). If thisbehavior is not desired, guard the call by checking_Py_IsFinalizing()orsys.is_finalizing().(Contributed by Joannah Nanjekye inbpo-36475.)

Changes in the Python API¶

• Theos.getcwdb() function now uses the UTF-8 encoding on Windows,rather than the ANSI code page: seePEP 529 for the rationale. Thefunction is no longer deprecated on Windows.(Contributed by Victor Stinner inbpo-37412.)

• subprocess.Popen can now useos.posix_spawn() in some casesfor better performance. On Windows Subsystem for Linux and QEMU UserEmulation, thePopen constructor usingos.posix_spawn() no longer raises anexception on errors like “missing program”. Instead the child process fails with anon-zeroreturncode.(Contributed by Joannah Nanjekye and Victor Stinner inbpo-35537.)

• Thepreexec_fn argument of *subprocess.Popen is no longercompatible with subinterpreters. The use of the parameter in asubinterpreter now raisesRuntimeError.(Contributed by Eric Snow inbpo-34651, modified by Christian Heimesinbpo-37951.)

• Theimap.IMAP4.logout() method no longer silently ignores arbitraryexceptions.(Contributed by Victor Stinner inbpo-36348.)

• The functionplatform.popen() has been removed, after having been deprecated sincePython 3.3: useos.popen() instead.(Contributed by Victor Stinner inbpo-35345.)

• Thestatistics.mode() function no longer raises an exceptionwhen given multimodal data. Instead, it returns the first modeencountered in the input data. (Contributed by Raymond Hettingerinbpo-35892.)

• Theselection() method of thetkinter.ttk.Treeview class no longer takes arguments. Using it witharguments for changing the selection was deprecated in Python 3.6. Usespecialized methods likeselection_set() forchanging the selection. (Contributed by Serhiy Storchaka inbpo-31508.)

• Thewritexml(),toxml() andtoprettyxml() methods ofxml.dom.minidom, and thewrite() method ofxml.etree,now preserve the attribute order specified by the user.(Contributed by Diego Rojas and Raymond Hettinger inbpo-34160.)

• Adbm.dumb database opened with flags'r' is now read-only.dbm.dumb.open() with flags'r' and'w' no longer createsa database if it does not exist.(Contributed by Serhiy Storchaka inbpo-32749.)

• Thedoctype() method defined in a subclass ofXMLParser will no longer be called and willemit aRuntimeWarning instead of aDeprecationWarning.Define thedoctype()method on a target for handling an XML doctype declaration.(Contributed by Serhiy Storchaka inbpo-29209.)

• ARuntimeError is now raised when the custom metaclass doesn’tprovide the__classcell__ entry in the namespace passed totype.__new__. ADeprecationWarning was emitted in Python3.6–3.7. (Contributed by Serhiy Storchaka inbpo-23722.)

• ThecProfile.Profile class can now be used as a contextmanager. (Contributed by Scott Sanderson inbpo-29235.)

• shutil.copyfile(),shutil.copy(),shutil.copy2(),shutil.copytree() andshutil.move() use platform-specific“fast-copy” syscalls (seePlatform-dependent efficient copy operations section).

• shutil.copyfile() default buffer size on Windows was changed from16 KiB to 1 MiB.

• ThePyGC_Head struct has changed completely. All code that touched thestruct member should be rewritten. (Seebpo-33597.)

• ThePyInterpreterState struct has been moved into the “internal”header files (specifically Include/internal/pycore_pystate.h). AnopaquePyInterpreterState is still available as part of the publicAPI (and stable ABI). The docs indicate that none of the struct’sfields are public, so we hope no one has been using them. However,if you do rely on one or more of those private fields and have noalternative then please open a BPO issue. We’ll work on helpingyou adjust (possibly including adding accessor functions to thepublic API). (Seebpo-35886.)

• Themmap.flush() method now returnsNone onsuccess and raises an exception on error under all platforms. Previously,its behavior was platform-dependent: a nonzero value was returned on success;zero was returned on error under Windows. A zero value was returned onsuccess; an exception was raised on error under Unix.(Contributed by Berker Peksag inbpo-2122.)

• xml.dom.minidom andxml.sax modules no longer processexternal entities by default.(Contributed by Christian Heimes inbpo-17239.)

• Deleting a key from a read-onlydbm database (dbm.dumb,dbm.gnu ordbm.ndbm) raiseserror (dbm.dumb.error,dbm.gnu.error ordbm.ndbm.error) instead ofKeyError.(Contributed by Xiang Zhang inbpo-33106.)

• Simplified AST for literals. All constants will be represented asast.Constant instances. Instantiating old classesNum,Str,Bytes,NameConstant andEllipsis will returnan instance ofConstant.(Contributed by Serhiy Storchaka inbpo-32892.)

• expanduser() on Windows now prefers theUSERPROFILEenvironment variable and does not useHOME, which is not normallyset for regular user accounts.(Contributed by Anthony Sottile inbpo-36264.)

• The exceptionasyncio.CancelledError now inherits fromBaseException rather thanException and no longer inheritsfromconcurrent.futures.CancelledError.(Contributed by Yury Selivanov inbpo-32528.)

• The functionasyncio.wait_for() now correctly waits for cancellationwhen using an instance ofasyncio.Task. Previously, upon reachingtimeout, it was cancelled and immediately returned.(Contributed by Elvis Pranskevichus inbpo-32751.)

• The functionasyncio.BaseTransport.get_extra_info() now returns a safeto use socket object when ‘socket’ is passed to thename parameter.(Contributed by Yury Selivanov inbpo-37027.)

• asyncio.BufferedProtocol has graduated to the stable API.

• DLL dependencies for extension modules and DLLs loaded withctypes onWindows are now resolved more securely. Only the system paths, the directorycontaining the DLL or PYD file, and directories added withadd_dll_directory() are searched for load-time dependencies.Specifically,PATH and the current working directory are no longerused, and modifications to these will no longer have any effect on normal DLLresolution. If your application relies on these mechanisms, you should checkforadd_dll_directory() and if it exists, use it to add your DLLsdirectory while loading your library. Note that Windows 7 users will need toensure that Windows Update KB2533623 has been installed (this is also verifiedby the installer).(Contributed by Steve Dower inbpo-36085.)

• The header files and functions related to pgen have been removed after itsreplacement by a pure Python implementation. (Contributed by Pablo Galindoinbpo-36623.)

• types.CodeType has a new parameter in the second position of theconstructor (posonlyargcount) to support positional-only arguments definedinPEP 570. The first argument (argcount) now represents the totalnumber of positional arguments (including positional-only arguments). The newreplace() method oftypes.CodeType can be used to make the codefuture-proof.

• The parameterdigestmod forhmac.new() no longer uses the MD5 digestby default.

Changes in the C API¶

• ThePyCompilerFlags structure got a newcf_feature_versionfield. It should be initialized toPY_MINOR_VERSION. The field is ignoredby default, and is used if and only ifPyCF_ONLY_AST flag is set incf_flags.(Contributed by Guido van Rossum inbpo-35766.)

• ThePyEval_ReInitThreads() function has been removed from the C API.It should not be called explicitly: usePyOS_AfterFork_Child()instead.(Contributed by Victor Stinner inbpo-36728.)

• On Unix, C extensions are no longer linked to libpython except on Androidand Cygwin. When Python is embedded,libpython must not be loaded withRTLD_LOCAL, butRTLD_GLOBAL instead. Previously, usingRTLD_LOCAL, it was already not possible to load C extensions whichwere not linked tolibpython, like C extensions of the standardlibrary built by the*shared* section ofModules/Setup.(Contributed by Victor Stinner inbpo-21536.)

• Use of# variants of formats in parsing or building value (e.g.PyArg_ParseTuple(),Py_BuildValue(),PyObject_CallFunction(),etc.) withoutPY_SSIZE_T_CLEAN defined raisesDeprecationWarning now.It will be removed in 3.10 or 4.0. ReadParsing arguments and building values for detail.(Contributed by Inada Naoki inbpo-36381.)

• Instances of heap-allocated types (such as those created withPyType_FromSpec()) hold a reference to their type object.Increasing the reference count of these type objects has been moved fromPyType_GenericAlloc() to the more low-level functions,PyObject_Init() andPyObject_INIT().This makes types created throughPyType_FromSpec() behave likeother classes in managed code.

  Statically allocated types are not affected.

  For the vast majority of cases, there should be no side effect.However, types that manually increase the reference count after allocatingan instance (perhaps to work around the bug) may now become immortal.To avoid this, these classes need to call Py_DECREF on the type objectduring instance deallocation.

  To correctly port these types into 3.8, please apply the followingchanges:

  • RemovePy_INCREF on the type object after allocating aninstance - if any.This may happen after callingPyObject_New(),PyObject_NewVar(),PyObject_GC_New(),PyObject_GC_NewVar(), or any other custom allocator that usesPyObject_Init() orPyObject_INIT().

    Example:

    staticfoo_struct*foo_new(PyObject*type){foo_struct*foo=PyObject_GC_New(foo_struct,(PyTypeObject*)type);if(foo==NULL)returnNULL;#if PY_VERSION_HEX < 0x03080000// Workaround for Python issue 35810; no longer necessary in Python 3.8PY_INCREF(type)#endifreturnfoo;}

  • Ensure that all customtp_dealloc functions of heap-allocated typesdecrease the type’s reference count.

    Example:

    staticvoidfoo_dealloc(foo_struct*instance){PyObject*type=Py_TYPE(instance);PyObject_GC_Del(instance);#if PY_VERSION_HEX >= 0x03080000// This was not needed before Python 3.8 (Python issue 35810)Py_DECREF(type);#endif}

  (Contributed by Eddie Elizondo inbpo-35810.)

• ThePy_DEPRECATED() macro has been implemented for MSVC.The macro now must be placed before the symbol name.

  Example:

  Py_DEPRECATED(3.8)PyAPI_FUNC(int)Py_OldFunction(void);

  (Contributed by Zackery Spytz inbpo-33407.)

• The interpreter does not pretend to support binary compatibility ofextension types across feature releases, anymore. APyTypeObjectexported by a third-party extension module is supposed to have all theslots expected in the current Python version, includingtp_finalize (Py_TPFLAGS_HAVE_FINALIZEis not checked anymore before readingtp_finalize).

  (Contributed by Antoine Pitrou inbpo-32388.)

• The functionsPyNode_AddChild() andPyParser_AddToken() now accepttwo additionalint argumentsend_lineno andend_col_offset.

• Thelibpython38.a file to allow MinGW tools to link directly againstpython38.dll is no longer included in the regular Windows distribution.If you require this file, it may be generated with thegendef anddlltool tools, which are part of the MinGW binutils package:

  gendef-python38.dll>tmp.defdlltool--dllnamepython38.dll--deftmp.def--output-liblibpython38.a

  The location of an installedpythonXY.dll will depend on theinstallation options and the version and language of Windows. SeeUsing Python on Windows for more information. The resulting library should beplaced in the same directory aspythonXY.lib, which is generally thelibs directory under your Python installation.

  (Contributed by Steve Dower inbpo-37351.)

CPython bytecode changes¶

• The interpreter loop has been simplified by moving the logic of unrollingthe stack of blocks into the compiler. The compiler emits now explicitinstructions for adjusting the stack of values and calling thecleaning-up code forbreak,continue andreturn.

  Removed opcodesBREAK_LOOP,CONTINUE_LOOP,SETUP_LOOP andSETUP_EXCEPT. Added new opcodesROT_FOUR,BEGIN_FINALLY,CALL_FINALLY andPOP_FINALLY. Changed the behavior ofEND_FINALLYandWITH_CLEANUP_START.

  (Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka inbpo-17611.)

• Added new opcodeEND_ASYNC_FOR for handling exceptions raisedwhen awaiting a next item in anasyncfor loop.(Contributed by Serhiy Storchaka inbpo-33041.)

• TheMAP_ADD now expects the value as the first element in thestack and the key as the second element. This change was made so the keyis always evaluated before the value in dictionary comprehensions, asproposed byPEP 572. (Contributed by Jörn Heissler inbpo-35224.)

Demos and Tools¶

Added a benchmark script for timing various ways to access variables:Tools/scripts/var_access_benchmark.py.(Contributed by Raymond Hettinger inbpo-35884.)

Here’s a summary of performance improvements since Python 3.3:

Python version                       3.3     3.4     3.5     3.6     3.7     3.8--------------                       ---     ---     ---     ---     ---     ---Variable and attribute read access:    read_local                       4.0     7.1     7.1     5.4     5.1     3.9    read_nonlocal                    5.3     7.1     8.1     5.8     5.4     4.4    read_global                     13.3    15.5    19.0    14.3    13.6     7.6    read_builtin                    20.0    21.1    21.6    18.5    19.0     7.5    read_classvar_from_class        20.5    25.6    26.5    20.7    19.5    18.4    read_classvar_from_instance     18.5    22.8    23.5    18.8    17.1    16.4    read_instancevar                26.8    32.4    33.1    28.0    26.3    25.4    read_instancevar_slots          23.7    27.8    31.3    20.8    20.8    20.2    read_namedtuple                 68.5    73.8    57.5    45.0    46.8    18.4    read_boundmethod                29.8    37.6    37.9    29.6    26.9    27.7Variable and attribute write access:    write_local                      4.6     8.7     9.3     5.5     5.3     4.3    write_nonlocal                   7.3    10.5    11.1     5.6     5.5     4.7    write_global                    15.9    19.7    21.2    18.0    18.0    15.8    write_classvar                  81.9    92.9    96.0   104.6   102.1    39.2    write_instancevar               36.4    44.6    45.8    40.0    38.9    35.5    write_instancevar_slots         28.7    35.6    36.1    27.3    26.6    25.7Data structure read access:    read_list                       19.2    24.2    24.5    20.8    20.8    19.0    read_deque                      19.9    24.7    25.5    20.2    20.6    19.8    read_dict                       19.7    24.3    25.7    22.3    23.0    21.0    read_strdict                    17.9    22.6    24.3    19.5    21.2    18.9Data structure write access:    write_list                      21.2    27.1    28.5    22.5    21.6    20.0    write_deque                     23.8    28.7    30.1    22.7    21.8    23.5    write_dict                      25.9    31.4    33.3    29.3    29.2    24.7    write_strdict                   22.9    28.4    29.9    27.5    25.2    23.1Stack (or queue) operations:    list_append_pop                144.2    93.4   112.7    75.4    74.2    50.8    deque_append_pop                30.4    43.5    57.0    49.4    49.2    42.5    deque_append_popleft            30.8    43.7    57.3    49.7    49.7    42.8Timing loop:    loop_overhead                    0.3     0.5     0.6     0.4     0.3     0.3

The benchmarks were measured on anIntel® Core™ i7-4960HQ processorrunning the macOS 64-bit builds found atpython.org.The benchmark script displays timings in nanoseconds.