PEP 453: Explicit Bootstrapping of PIP in Python Installations¶

PEP 446: Newly Created File Descriptors Are Non-Inheritable¶

PEP 446 makes newly created file descriptorsnon-inheritable. In general, this is the behavior an application willwant: when launching a new process, having currently open files alsoopen in the new process can lead to all sorts of hard to find bugs,and potentially to security issues.

However, there are occasions when inheritance is desired. To supportthese cases, the following new functions and methods are available:

• os.get_inheritable()、os.set_inheritable()

• os.get_handle_inheritable()、os.set_handle_inheritable()

• socket.socket.get_inheritable()、socket.socket.set_inheritable()

編解碼器處理的改進¶

Since it was first introduced, thecodecs module has always beenintended to operate as a type-neutral dynamic encoding and decodingsystem. However, its close coupling with the Python text model, especiallythe type restricted convenience methods on the builtinstr,bytes andbytearray types, has historically obscured thatfact.

As a key step in clarifying the situation, thecodecs.encode() andcodecs.decode() convenience functions are now properly documented inPython 2.7, 3.3 and 3.4. These functions have existed in thecodecsmodule (and have been covered by the regression test suite) since Python 2.4,but were previously only discoverable through runtime introspection.

Unlike the convenience methods onstr,bytes andbytearray, thecodecs convenience functions support arbitrarycodecs in both Python 2 and Python 3, rather than being limited to Unicode textencodings (in Python 3) orbasestring <->basestring conversions (inPython 2).

In Python 3.4, the interpreter is able to identify the known non-textencodings provided in the standard library and direct users towards thesegeneral purpose convenience functions when appropriate:

>>>b"abcdef".decode("hex")Traceback (most recent call last):  File"<stdin>", line1, in<module>LookupError:'hex' is not a text encoding; use codecs.decode() to handle arbitrary codecs>>>"hello".encode("rot13")Traceback (most recent call last):  File"<stdin>", line1, in<module>LookupError:'rot13' is not a text encoding; use codecs.encode() to handle arbitrary codecs>>>open("foo.txt",encoding="hex")Traceback (most recent call last):  File"<stdin>", line1, in<module>LookupError:'hex' is not a text encoding; use codecs.open() to handle arbitrary codecs

In a related change, whenever it is feasible without breaking backwardscompatibility, exceptions raised during encoding and decoding operationsare wrapped in a chained exception of the same type that mentions thename of the codec responsible for producing the error:

>>>importcodecs>>>codecs.decode(b"abcdefgh","hex")Traceback (most recent call last):  File"/usr/lib/python3.4/encodings/hex_codec.py", line20, inhex_decodereturn(binascii.a2b_hex(input),len(input))binascii.Error:Non-hexadecimal digit foundThe above exception was the direct cause of the following exception:Traceback (most recent call last):  File"<stdin>", line1, in<module>binascii.Error:decoding with 'hex' codec failed (Error: Non-hexadecimal digit found)>>>codecs.encode("hello","bz2")Traceback (most recent call last):  File"/usr/lib/python3.4/encodings/bz2_codec.py", line17, inbz2_encodereturn(bz2.compress(input),len(input))  File"/usr/lib/python3.4/bz2.py", line498, incompressreturncomp.compress(data)+comp.flush()TypeError:'str' does not support the buffer interfaceThe above exception was the direct cause of the following exception:Traceback (most recent call last):  File"<stdin>", line1, in<module>TypeError:encoding with 'bz2' codec failed (TypeError: 'str' does not support the buffer interface)

Finally, as the examples above show, these improvements have permittedthe restoration of the convenience aliases for the non-Unicode codecs thatwere themselves restored in Python 3.2. This means that encoding binary datato and from its hexadecimal representation (for example) can now be writtenas:

>>>fromcodecsimportencode,decode>>>encode(b"hello","hex")b'68656c6c6f'>>>decode(b"68656c6c6f","hex")b'hello'

The binary and text transforms provided in the standard library are detailedinBinary Transforms andText Transforms.

（由 Nick Coghlan 在bpo-7475、bpo-17827、bpo-17828 和bpo-19619 中貢獻。）

PEP 451：用於引入系統的 ModuleSpec 型別¶

PEP 451 provides an encapsulation of the information about a module that theimport machinery will use to load it (that is, a module specification). Thishelps simplify both the import implementation and several import-related APIs.The change is also a stepping stone forseveral future import-relatedimprovements.

The public-facing changes from the PEP are entirely backward-compatible.Furthermore, they should be transparent to everyone but importer authors. Keyfinder and loader methods have been deprecated, but they will continue working.New importers should use the new methods described in the PEP. Existingimporters should be updated to implement the new methods. See the已棄用 section for a list of methods that should be replaced andtheir replacements.

其他語言更動¶

Some smaller changes made to the core Python language are:

• Unicode database updated to UCD version 6.3.

• min() andmax() now accept adefault keyword-only argument thatcan be used to specify the value they return if the iterable they areevaluating has no elements. (Contributed by Julian Berman inbpo-18111.)

• Module objects are nowweakly referenceable.

• Module__file__ attributes (and related values) should now alwayscontain absolute paths by default, with the sole exception of__main__.__file__ when a script has been executed directly usinga relative path. (Contributed by Brett Cannon inbpo-18416.)

• All the UTF-* codecs (except UTF-7) now reject surrogates during bothencoding and decoding unless thesurrogatepass error handler is used,with the exception of the UTF-16 decoder (which accepts valid surrogate pairs)and the UTF-16 encoder (which produces them while encoding non-BMP characters).(Contributed by Victor Stinner, Kang-Hao (Kenny) Lu and Serhiy Storchaka inbpo-12892.)

• New German EBCDICcodeccp273. (Contributedby Michael Bierenfeld and Andrew Kuchling inbpo-1097797.)

• New Ukrainiancodeccp1125. (Contributed bySerhiy Storchaka inbpo-19668.)

• bytes.join() andbytearray.join() now accept arbitrarybuffer objects as arguments. (Contributed by Antoine Pitrou inbpo-15958.)

• Theint constructor now accepts any object that has an__index__method for itsbase argument. (Contributed by Mark Dickinson inbpo-16772.)

• Frame objects now have aclear() method that clears allreferences to local variables from the frame. (Contributed by Antoine Pitrouinbpo-17934.)

• memoryview is now registered as aSequence,and supports thereversed() builtin. (Contributed by Nick Coghlanand Claudiu Popa inbpo-18690 andbpo-19078.)

• Signatures reported byhelp() have been modified and improved inseveral cases as a result of the introduction of Argument Clinic and otherchanges to theinspect andpydoc modules.

• __length_hint__() is now part of the formal languagespecification (seePEP 424). (Contributed by Armin Ronacher inbpo-16148.)

asyncio¶

The newasyncio module (defined inPEP 3156) provides a standardpluggable event loop model for Python, providing solid asynchronous IOsupport in the standard library, and making it easier for other event loopimplementations to interoperate with the standard library and each other.

For Python 3.4, this module is considered aprovisional API.

ensurepip¶

The newensurepip module is the primary infrastructure for thePEP 453 implementation. In the normal course of events end users will notneed to interact with this module, but it can be used to manually bootstrappip if the automated bootstrapping into an installation or virtualenvironment was declined.

ensurepip includes a bundled copy ofpip, up-to-date as of the firstrelease candidate of the release of CPython with which it ships (this appliesto both maintenance releases and feature releases).ensurepip does notaccess the internet. If the installation has internet access, afterensurepip is run the bundledpip can be used to upgradepip to amore recent release than the bundled one. (Note that such an upgraded versionofpip is considered to be a separately installed package and will not beremoved if Python is uninstalled.)

The module is namedensurepip because if called whenpip is alreadyinstalled, it does nothing. It also has an--upgrade option that willcause it to install the bundled copy ofpip if the existing installedversion ofpip is older than the bundled copy.

enum¶

The newenum module (defined inPEP 435) provides a standardimplementation of enumeration types, allowing other modules (such assocket) to provide more informative error messages and betterdebugging support by replacing opaque integer constants with backwardscompatible enumeration values.

pathlib¶

The newpathlib module offers classes representing filesystem pathswith semantics appropriate for different operating systems. Path classes aredivided betweenpure paths, which provide purely computational operationswithout I/O, andconcrete paths, which inherit from pure paths but alsoprovide I/O operations.

For Python 3.4, this module is considered aprovisional API.

selectors¶

The newselectors module (created as part of implementingPEP 3156)allows high-level and efficient I/O multiplexing, built upon theselect module primitives.

statistics¶

The newstatistics module (defined inPEP 450) offers some corestatistics functionality directly in the standard library. This modulesupports calculation of the mean, median, mode, variance and standarddeviation of a data series.

tracemalloc¶

The newtracemalloc module (defined inPEP 454) is a debug tool totrace memory blocks allocated by Python. It provides the following information:

• Trace where an object was allocated

• Statistics on allocated memory blocks per filename and per line number:total size, number and average size of allocated memory blocks

• Compute the differences between two snapshots to detect memory leaks

abc¶

New functionabc.get_cache_token() can be used to know when to invalidatecaches that are affected by changes in the object graph. (Contributedby Łukasz Langa inbpo-16832.)

New classABC hasABCMeta as its meta class.UsingABC as a base class has essentially the same effect as specifyingmetaclass=abc.ABCMeta, but is simpler to type and easier to read.(Contributed by Bruno Dupuis inbpo-16049.)

aifc¶

Thegetparams() method now returns a namedtuple rather than aplain tuple. (Contributed by Claudiu Popa inbpo-17818.)

aifc.open() now supports the context management protocol: when used in awith block, theclose() method of the returnedobject will be called automatically at the end of the block. (Contributed bySerhiy Storchacha inbpo-16486.)

Thewriteframesraw() andwriteframes()methods now accept anybytes-like object. (Contributed by SerhiyStorchaka inbpo-8311.)

argparse¶

TheFileType class now acceptsencoding anderrors arguments, which are passed through toopen(). (Contributedby Lucas Maystre inbpo-11175.)

audioop¶

audioop now supports 24-bit samples. (Contributed by Serhiy Storchakainbpo-12866.)

Newbyteswap() function converts big-endian samples tolittle-endian and vice versa. (Contributed by Serhiy Storchaka inbpo-19641.)

Allaudioop functions now accept anybytes-like object. Stringsare not accepted: they didn't work before, now they raise an error right away.(Contributed by Serhiy Storchaka inbpo-16685.)

base64¶

The encoding and decoding functions inbase64 now accept anybytes-like object in cases where it previously required abytes orbytearray instance. (Contributed by Nick Coghlan inbpo-17839.)

New functionsa85encode(),a85decode(),b85encode(), andb85decode() provide the ability toencode and decode binary data from and toAscii85 and the git/mercurialBase85 formats, respectively. Thea85 functions have options that canbe used to make them compatible with the variants of theAscii85 encoding,including the Adobe variant. (Contributed by Martin Morrison, the Mercurialproject, Serhiy Storchaka, and Antoine Pitrou inbpo-17618.)

collections¶

TheChainMap.new_child() method now accepts anm argument specifyingthe child map to add to the chain. This allows an existing mapping and/or acustom mapping type to be used for the child. (Contributed by Vinay Sajip inbpo-16613.)

colorsys¶

The number of digits in the coefficients for the RGB --- YIQ conversions havebeen expanded so that they match the FCC NTSC versions. The change inresults should be less than 1% and may better match results found elsewhere.(Contributed by Brian Landers and Serhiy Storchaka inbpo-14323.)

contextlib¶

The newcontextlib.suppress context manager helps to clarify theintent of code that deliberately suppresses exceptions from a singlestatement. (Contributed by Raymond Hettinger inbpo-15806 andZero Piraeus inbpo-19266.)

The newcontextlib.redirect_stdout() context manager makes it easierfor utility scripts to handle inflexible APIs that write their output tosys.stdout and don't provide any options to redirect it. Using thecontext manager, thesys.stdout output can be redirected to anyother stream or, in conjunction withio.StringIO, to a string.The latter can be especially useful, for example, to capture outputfrom a function that was written to implement a command line interface.It is recommended only for utility scripts because it affects theglobal state ofsys.stdout. (Contributed by Raymond Hettingerinbpo-15805.)

Thecontextlib documentation has also been updated to include adiscussion of thedifferences between single use, reusable and reentrant context managers.

dbm¶

dbm.open() objects now support the context management protocol. Whenused in awith statement, theclose method of the databaseobject will be called automatically at the end of the block. (Contributed byClaudiu Popa and Nick Coghlan inbpo-19282.)

dis¶

Functionsshow_code(),dis(),distb(), anddisassemble() now accept a keyword-onlyfile argument thatcontrols where they write their output.

Thedis module is now built around anInstruction classthat provides object oriented access to the details of each individual bytecodeoperation.

A new method,get_instructions(), provides an iterator that emitsthe Instruction stream for a given piece of Python code. Thus it is nowpossible to write a program that inspects and manipulates a bytecodeobject in ways different from those provided by thedis moduleitself. For example:

>>>importdis>>>forinstrindis.get_instructions(lambdax:x+1):...print(instr.opname)LOAD_FASTLOAD_CONSTBINARY_ADDRETURN_VALUE

The various display tools in thedis module have been rewritten to usethese new components.

In addition, a new application-friendly classBytecode providesan object-oriented API for inspecting bytecode in both in human-readable formand for iterating over instructions. TheBytecode constructortakes the same arguments thatget_instruction() does (plus anoptionalcurrent_offset), and the resulting object can be iterated to produceInstruction objects. But it also has adismethod, equivalent to callingdis on the constructor argument, butreturned as a multi-line string:

>>>bytecode=dis.Bytecode(lambdax:x+1,current_offset=3)>>>forinstrinbytecode:...print('{} ({})'.format(instr.opname,instr.opcode))LOAD_FAST (124)LOAD_CONST (100)BINARY_ADD (23)RETURN_VALUE (83)>>>bytecode.dis().splitlines()['  1           0 LOAD_FAST                0 (x)', '      -->     3 LOAD_CONST               1 (1)', '              6 BINARY_ADD', '              7 RETURN_VALUE']

Bytecode also has a class method,from_traceback(), that provides the ability to manipulate atraceback (that is,print(Bytecode.from_traceback(tb).dis()) is equivalenttodistb(tb)).

（由 Nick Coghlan、Ryan Kelly 和 Thomas Kluyver 在bpo-11816 中以及 Claudiu Popa 在bpo-17916 中貢獻。）

New functionstack_effect() computes the effect on the Python stackof a given opcode and argument, information that is not otherwise available.(Contributed by Larry Hastings inbpo-19722.)

doctest¶

A newoption flag,FAIL_FAST, haltstest running as soon as the first failure is detected. (Contributed by R.David Murray and Daniel Urban inbpo-16522.)

Thedoctest command line interface now usesargparse, and has twonew options,-o and-f.-o allowsdoctest options to be specified on the command line, and-f is ashorthand for-oFAIL_FAST (to parallel the similar option supported by theunittest CLI). (Contributed by R. David Murray inbpo-11390.)

doctest will now find doctests in extension module__doc__ strings.(Contributed by Zachary Ware inbpo-3158.)

email¶

as_string() now accepts apolicy argument tooverride the default policy of the message when generating a stringrepresentation of it. This means thatas_string can now be used in morecircumstances, instead of having to create and use agenerator inorder to pass formatting parameters to itsflatten method. (Contributed byR. David Murray inbpo-18600.)

New methodas_bytes() added to produce a bytesrepresentation of the message in a fashion similar to howas_stringproduces a string representation. It does not accept themaxheaderlenargument, but does accept theunixfrom andpolicy arguments. TheMessage__bytes__() methodcalls it, meaning thatbytes(mymsg) will now produce the intuitiveresult: a bytes object containing the fully formatted message. (Contributedby R. David Murray inbpo-18600.)

TheMessage.set_param() message now accepts areplace keyword argument.When specified, the associated header will be updated without changingits location in the list of headers. For backward compatibility, the defaultisFalse. (Contributed by R. David Murray inbpo-18891.)

A pair of new subclasses ofMessage have been added(EmailMessage andMIMEPart), along with a new sub-module,contentmanager and a newpolicy attributecontent_manager. All documentation iscurrently in the new module, which is being added as part of email's newprovisional API. These classes provide a number of new methods thatmake extracting content from and inserting content into email messages mucheasier. For details, see thecontentmanager documentation andtheemail：範例. These API additions complete thebulk of the work that was planned as part of the email6 project. The currentlyprovisional API is scheduled to become final in Python 3.5 (possibly with a fewminor additions in the area of error handling). (Contributed by R. DavidMurray inbpo-18891.)

filecmp¶

A newclear_cache() function provides the ability to clear thefilecmp comparison cache, which usesos.stat() information todetermine if the file has changed since the last compare. This can be used,for example, if the file might have been changed and re-checked in less timethan the resolution of a particular filesystem's file modification time field.(Contributed by Mark Levitt inbpo-18149.)

New module attributeDEFAULT_IGNORES provides the list ofdirectories that are used as the default value for theignore parameter ofthedircmp() function. (Contributed by Eli Bendersky inbpo-15442.)

functools¶

The newpartialmethod() descriptor brings partial argumentapplication to descriptors, just aspartial() providesfor normal callables. The new descriptor also makes it easier to getarbitrary callables (includingpartial() instances)to behave like normal instance methods when included in a class definition.(Contributed by Alon Horev and Nick Coghlan inbpo-4331.)

The newsingledispatch() decorator brings support forsingle-dispatch generic functions to the Python standard library. Whereobject oriented programming focuses on grouping multiple operations on acommon set of data into a class, a generic function focuses on groupingmultiple implementations of an operation that allows it to work withdifferent kinds of data.

total_ordering() now supports a return value ofNotImplemented from the underlying comparison function. (Contributedby Katie Miller inbpo-10042.)

A pure-python version of thepartial() function is now in thestdlib; in CPython it is overridden by the C accelerated version, but it isavailable for other implementations to use. (Contributed by Brian Thorne inbpo-12428.)

gc¶

New functionget_stats() returns a list of three per-generationdictionaries containing the collections statistics since interpreter startup.(Contributed by Antoine Pitrou inbpo-16351.)

glob¶

A new functionescape() provides a way to escape special charactersin a filename so that they do not become part of the globbing expansion but areinstead matched literally. (Contributed by Serhiy Storchaka inbpo-8402.)

hashlib¶

新的hashlib.pbkdf2_hmac() 函式提供了基於密碼的 PKCS#5 密鑰生成函式 2。（由 Christian Heimes 在bpo-18582 中貢獻。）

Thename attribute ofhashlib hash objects is nowa formally supported interface. It has always existed in CPython'shashlib (although it did not return lower case names for all supportedhashes), but it was not a public interface and so some other Pythonimplementations have not previously supported it. (Contributed by Jason R.Coombs inbpo-18532.)

hmac¶

hmac now acceptsbytearray as well asbytes for thekeyargument to thenew() function, and themsg parameter to both thenew() function and theupdate() method nowaccepts any type supported by thehashlib module. (Contributedby Jonas Borgström inbpo-18240.)

Thedigestmod argument to thehmac.new() function may now be any hashdigest name recognized byhashlib. In addition, the current behavior inwhich the value ofdigestmod defaults toMD5 is deprecated: in afuture version of Python there will be no default value. (Contributed byChristian Heimes inbpo-17276.)

With the addition ofblock_size andnameattributes (and the formal documentation of thedigest_sizeattribute), thehmac module now conforms fully to thePEP 247 API.(Contributed by Christian Heimes inbpo-18775.)

html¶

New functionunescape() function converts HTML5 character references tothe corresponding Unicode characters. (Contributed by Ezio Melotti inbpo-2927.)

HTMLParser accepts a new keyword argumentconvert_charrefs that, whenTrue, automatically converts all characterreferences. For backward-compatibility, its value defaults toFalse, butit will change toTrue in a future version of Python, so you are invited toset it explicitly and update your code to use this new feature. (Contributedby Ezio Melotti inbpo-13633.)

Thestrict argument ofHTMLParser is now deprecated.(Contributed by Ezio Melotti inbpo-15114.)

http¶

send_error() now accepts anoptional additionalexplain parameter which can be used to provide anextended error description, overriding the hardcoded default if there is one.This extended error description will be formatted using theerror_message_format attribute and sent as the bodyof the error response. (Contributed by Karl Cow inbpo-12921.)

Thehttp.servercommand line interface now hasa-b/--bind option that causes the server to listen on a specific address.(Contributed by Malte Swart inbpo-17764.)

idlelib 與 IDLE¶

Since idlelib implements the IDLE shell and editor and is not intended forimport by other programs, it gets improvements with every release. SeeLib/idlelib/NEWS.txt for a cumulative list of changes since 3.3.0,as well as changes made in future 3.4.x releases. This file is also availablefrom the IDLEHelp ‣ About IDLE dialog.

importlib¶

TheInspectLoader ABC defines a new method,source_to_code() that accepts sourcedata and a path and returns a code object. The default implementationis equivalent tocompile(data,path,'exec',dont_inherit=True).(Contributed by Eric Snow and Brett Cannon inbpo-15627.)

InspectLoader also now has a default implementationfor theget_code() method. However,it will normally be desirable to override the default implementationfor performance reasons. (Contributed by Brett Cannon inbpo-18072.)

Thereload() function has been moved fromimp toimportlib as part of theimp module deprecation. (Contributed byBerker Peksag inbpo-18193.)

importlib.util now has aMAGIC_NUMBER attributeproviding access to the bytecode version number. This replaces theget_magic() function in the deprecatedimp module.(Contributed by Brett Cannon inbpo-18192.)

Newimportlib.util functionscache_from_source()andsource_from_cache() replace the same-named functionsin the deprecatedimp module. (Contributed by Brett Cannon inbpo-18194.)

Theimportlib bootstrapNamespaceLoader now conforms totheInspectLoader ABC, which means thatrunpy andpython-m can now be used with namespace packages. (Contributedby Brett Cannon inbpo-18058.)

importlib.util has a new functiondecode_source()that decodes source from bytes using universal newline processing. This isuseful for implementingInspectLoader.get_source() methods.

importlib.machinery.ExtensionFileLoader now has aget_filename() method. This wasinadvertently omitted in the original implementation. (Contributed by EricSnow inbpo-19152.)

inspect¶

Theinspect module now offers a basiccommand line interface to quickly display source code and otherinformation for modules, classes and functions. (Contributed by Claudiu Popaand Nick Coghlan inbpo-18626.)

unwrap() makes it easy to unravel wrapper function chainscreated byfunctools.wraps() (and any other API that sets the__wrapped__ attribute on a wrapper function). (Contributed byDaniel Urban, Aaron Iles and Nick Coghlan inbpo-13266.)

As part of the implementation of the newenum module, theinspect module now has substantially better support for custom__dir__ methods and dynamic class attributes provided throughmetaclasses. (Contributed by Ethan Furman inbpo-18929 andbpo-19030.)

getfullargspec() andgetargspec()now use thesignature() API. This allows them tosupport a much broader range of callables, including those with__signature__ attributes, those with metadata provided by argumentclinic,functools.partial() objects and more. Note that, unlikesignature(), these functions still ignore__wrapped__attributes, and report the already bound first argument for bound methods,so it is still necessary to update your code to usesignature() directly if those features are desired.(Contributed by Yury Selivanov inbpo-17481.)

signature() now supports duck types of CPython functions,which adds support for functions compiled with Cython. (Contributedby Stefan Behnel and Yury Selivanov inbpo-17159.)

ipaddress¶

ipaddress was added to the standard library in Python 3.3 as aprovisional API. With the release of Python 3.4, this qualificationhas been removed:ipaddress is now considered a stable API, coveredby the normal standard library requirements to maintain backwardscompatibility.

A newis_global property isTrue ifan address is globally routeable. (Contributed by Peter Moody inbpo-17400.)

logging¶

TheTimedRotatingFileHandler has a newatTimeparameter that can be used to specify the time of day when rollover shouldhappen. (Contributed by Ronald Oussoren inbpo-9556.)

SocketHandler andDatagramHandler now support Unix domain sockets (bysettingport toNone). (Contributed by Vinay Sajip in commitce46195b56a9.)

fileConfig() now accepts aconfigparser.RawConfigParser subclass instance for thefnameparameter. This facilitates using a configuration file when loggingconfiguration is just a part of the overall application configuration, or wherethe application modifies the configuration before passing it tofileConfig(). (Contributed by Vinay Sajip inbpo-16110.)

Logging configuration data received from a socket via thelogging.config.listen() function can now be validated before beingprocessed by supplying a verification function as the argument to the newverify keyword argument. (Contributed by Vinay Sajip inbpo-15452.)

marshal¶

The defaultmarshal version has been bumped to 3. The code implementingthe new version restores the Python2 behavior of recording only one copy ofinterned strings and preserving the interning on deserialization, and extendsthis "one copy" ability to any object type (including handling recursivereferences). This reduces both the size of.pyc files and the amount ofmemory a module occupies in memory when it is loaded from a.pyc (or.pyo) file. (Contributed by Kristján Valur Jónsson inbpo-16475,with additional speedups by Antoine Pitrou inbpo-19219.)

mmap¶

mmap objects are nowweakly referenceable.(Contributed by Valerie Lambert inbpo-4885.)

multiprocessing¶

On Unix two newstart methods,spawn andforkserver, have been added for starting processes usingmultiprocessing. These make the mixing of processes with threads morerobust, and thespawn method matches the semantics that multiprocessing hasalways used on Windows. New functionget_all_start_methods() reports all start methodsavailable on the platform,get_start_method() reportsthe current start method, andset_start_method() setsthe start method. (Contributed by Richard Oudkerk inbpo-8713.)

multiprocessing also now has the concept of acontext, whichdetermines how child processes are created. New functionget_context() returns a context that uses a specifiedstart method. It has the same API as themultiprocessing module itself,so you can use it to createPools and otherobjects that will operate within that context. This allows a framework and anapplication or different parts of the same application to use multiprocessingwithout interfering with each other. (Contributed by Richard Oudkerk inbpo-18999.)

Except when using the oldfork start method, child processes no longerinherit unneeded handles/file descriptors from their parents (part ofbpo-8713).

multiprocessing now relies onrunpy (which implements the-m switch) to initialise__main__ appropriately in child processeswhen using thespawn orforkserver start methods. This resolves someedge cases where combining multiprocessing, the-m command line switch,and explicit relative imports could cause obscure failures in childprocesses. (Contributed by Nick Coghlan inbpo-19946.)

operator¶

New functionlength_hint() provides an implementation of thespecification for how the__length_hint__() special method shouldbe used, as part of thePEP 424 formal specification of this languagefeature. (Contributed by Armin Ronacher inbpo-16148.)

There is now a pure-python version of theoperator module available forreference and for use by alternate implementations of Python. (Contributed byZachary Ware inbpo-16694.)

os¶

There are new functions to get and set theinheritable flag of a file descriptor (os.get_inheritable(),os.set_inheritable()) or a Windows handle(os.get_handle_inheritable(),os.set_handle_inheritable()).

New functioncpu_count() reports the number of CPUs available on theplatform on which Python is running (orNone if the count can't bedetermined). Themultiprocessing.cpu_count() function is now implementedin terms of this function). (Contributed by Trent Nelson, Yogesh Chaudhari,Victor Stinner, and Charles-François Natali inbpo-17914.)

os.path.samestat() is now available on the Windows platform (and theos.path.samefile() implementation is now shared between Unix andWindows). (Contributed by Brian Curtin inbpo-11939.)

os.path.ismount() now recognizes volumes mounted below a driveroot on Windows. (Contributed by Tim Golden inbpo-9035.)

os.open() supports two new flags on platforms that provide them,O_PATH (un-opened file descriptor), andO_TMPFILE(unnamed temporary file; as of 3.4.0 release available only on Linux systemswith a kernel version of 3.11 or newer that have uapi headers). (Contributedby Christian Heimes inbpo-18673 and Benjamin Peterson, respectively.)

pdb¶

pdb has been enhanced to handle generators,yield, andyieldfrom in a more useful fashion. This is especially helpful whendebuggingasyncio based programs. (Contributed by Andrew Svetlov andXavier de Gaye inbpo-16596.)

Theprint command has been removed frompdb, restoring access to thePythonprint() function from the pdb command line. Python2'spdb didnot have aprint command; instead, enteringprint executed theprint statement. In Python3print was mistakenly made an alias for thepdbp command.p, however, prints therepr of its argument,not thestr like the Python2print command did. Worse, the Python3pdbprint command shadowed the Python3print function, making itinaccessible at thepdb prompt. (Contributed by Connor Osborn inbpo-18764.)

pickle¶

pickle now supports (but does not use by default) a new pickle protocol,protocol 4. This new protocol addresses a number of issues that were presentin previous protocols, such as the serialization of nested classes, very largestrings and containers, and classes whose__new__() method takeskeyword-only arguments. It also provides some efficiency improvements.

plistlib¶

plistlib now has an API that is similar to the standard pattern forstdlib serialization protocols, with newload(),dump(),loads(), anddumps()functions. (The older API is now deprecated.) In addition to the alreadysupported XML plist format (FMT_XML), it also now supportsthe binary plist format (FMT_BINARY). (Contributed by RonaldOussoren and others inbpo-14455.)

poplib¶

Two new methods have been added topoplib:capa(),which returns the list of capabilities advertised by the POP server, andstls(), which switches a clear-text POP3 session into anencrypted POP3 session if the POP server supports it. (Contributed by LorenzoCatucci inbpo-4473.)

pprint¶

Thepprint module'sPrettyPrinter class and itspformat(), andpprint() functions have a newoption,compact, that controls how the output is formatted. Currentlysettingcompact toTrue means that sequences will be printed with as manysequence elements as will fit withinwidth on each (indented) line.(Contributed by Serhiy Storchaka inbpo-19132.)

Long strings are now wrapped using Python's normal line continuationsyntax. (Contributed by Antoine Pitrou inbpo-17150.)

pty¶

pty.spawn() now returns the status value fromos.waitpid() onthe child process, instead ofNone. (Contributed by Gregory P. Smith.)

pydoc¶

Thepydoc module is now based directly on theinspect.signature()introspection API, allowing it to provide signature information for a widervariety of callable objects. This change also means that__wrapped__attributes are now taken into account when displaying help information.(Contributed by Larry Hastings inbpo-19674.)

Thepydoc module no longer displays theself parameter foralready bound methods. Instead, it aims to always display the exact currentsignature of the supplied callable. (Contributed by Larry Hastings inbpo-20710.)

In addition to the changes that have been made topydoc directly,its handling of custom__dir__ methods and various descriptorbehaviours has also been improved substantially by the underlying changes intheinspect module.

As thehelp() builtin is based onpydoc, the above changes alsoaffect the behaviour ofhelp().

re¶

Newfullmatch() function andregex.fullmatch() method anchorthe pattern at both ends of the string to match. This provides a way to beexplicit about the goal of the match, which avoids a class of subtle bugs where$ characters get lost during code changes or the addition of alternativesto an existing regular expression. (Contributed by Matthew Barnett inbpo-16203.)

The repr ofregex objects now includes the patternand the flags; the repr ofmatch objects nowincludes the start, end, and the part of the string that matched. (Contributedby Hugo Lopes Tavares and Serhiy Storchaka inbpo-13592 andbpo-17087.)

resource¶

Newprlimit() function, available on Linux platforms with akernel version of 2.6.36 or later and glibc of 2.13 or later, provides theability to query or set the resource limits for processes other than the onemaking the call. (Contributed by Christian Heimes inbpo-16595.)

On Linux kernel version 2.6.36 or later, there are also some newLinux specific constants:RLIMIT_MSGQUEUE,RLIMIT_NICE,RLIMIT_RTPRIO,RLIMIT_RTTIME, andRLIMIT_SIGPENDING.(Contributed by Christian Heimes inbpo-19324.)

On FreeBSD version 9 and later, there some new FreeBSD specific constants:RLIMIT_SBSIZE,RLIMIT_SWAP, andRLIMIT_NPTS. (Contributed by Claudiu Popa inbpo-19343.)

select¶

epoll objects now support the context management protocol.When used in awith statement, theclose()method will be called automatically at the end of the block. (Contributedby Serhiy Storchaka inbpo-16488.)

devpoll objects now havefileno() andclose() methods, as well as a new attributeclosed. (Contributed by Victor Stinner inbpo-18794.)

shelve¶

Shelf instances may now be used inwith statements,and will be automatically closed at the end of thewith block.(Contributed by Filip Gruszczyński inbpo-13896.)

shutil¶

copyfile() now raises a specificError subclass,SameFileError, when the source and destination are the samefile, which allows an application to take appropriate action on this specificerror. (Contributed by Atsuo Ishimoto and Hynek Schlawack inbpo-1492704.)

smtpd¶

TheSMTPServer andSMTPChannel classes nowaccept amap keyword argument which, if specified, is passed in toasynchat.async_chat as itsmap argument. This allows an applicationto avoid affecting the global socket map. (Contributed by Vinay Sajip inbpo-11959.)

smtplib¶

SMTPException is now a subclass ofOSError, which allowsboth socket level errors and SMTP protocol level errors to be caught in onetry/except statement by code that only cares whether or not an error occurred.(Contributed by Ned Jackson Lovely inbpo-2118.)

socket¶

The socket module now supports theCAN_BCM protocol onplatforms that support it. (Contributed by Brian Thorne inbpo-15359.)

Socket objects have new methods to get or set theirinheritable flag,get_inheritable() andset_inheritable().

Thesocket.AF_* andsocket.SOCK_* constants are now enumeration valuesusing the newenum module. This allows meaningful names to be printedduring debugging, instead of integer "magic numbers".

TheAF_LINK constant is now available on BSD and OSX.

inet_pton() andinet_ntop() are now supportedon Windows. (Contributed by Atsuo Ishimoto inbpo-7171.)

sqlite3¶

A new boolean parameter to theconnect() function,uri, can beused to indicate that thedatabase parameter is auri (see theSQLiteURI documentation). (Contributed by poq inbpo-13773.)

ssl¶

PROTOCOL_TLSv1_1 andPROTOCOL_TLSv1_2 (TLSv1.1 andTLSv1.2 support) have been added; support for these protocols is only available ifPython is linked with OpenSSL 1.0.1 or later. (Contributed by Michele Orrù andAntoine Pitrou inbpo-16692.)

New functioncreate_default_context() provides a standard way toobtain anSSLContext whose settings are intended to be areasonable balance between compatibility and security. These settings aremore stringent than the defaults provided by theSSLContextconstructor, and may be adjusted in the future, without prior deprecation, ifbest-practice security requirements change. The new recommended bestpractice for using stdlib libraries that support SSL is to usecreate_default_context() to obtain anSSLContextobject, modify it if needed, and then pass it as thecontext argumentof the appropriate stdlib API. (Contributed by Christian Heimesinbpo-19689.)

SSLContext methodload_verify_locations()accepts a new optional argumentcadata, which can be used to provide PEM orDER encoded certificates directly via strings or bytes, respectively.(Contributed by Christian Heimes inbpo-18138.)

New functionget_default_verify_paths() returnsa named tuple of the paths and environment variables that theset_default_verify_paths() method uses to setOpenSSL's defaultcafile andcapath. This can be an aid indebugging default verification issues. (Contributed by Christian Heimesinbpo-18143.)

SSLContext has a new method,cert_store_stats(), that reports the number of loadedX.509 certs,X.509CA certs, and certificate revocation lists(crls), as well as aget_ca_certs() method thatreturns a list of the loadedCA certificates. (Contributed by ChristianHeimes inbpo-18147.)

If OpenSSL 0.9.8 or later is available,SSLContext has a newattributeverify_flags that can be used to control thecertificate verification process by setting it to some combination of the newconstantsVERIFY_DEFAULT,VERIFY_CRL_CHECK_LEAF,VERIFY_CRL_CHECK_CHAIN, orVERIFY_X509_STRICT.OpenSSL does not do any CRL verification by default. (Contributed byChristien Heimes inbpo-8813.)

NewSSLContext methodload_default_certs()loads a set of default "certificate authority" (CA) certificates from defaultlocations, which vary according to the platform. It can be used to load bothTLS web server authentication certificates(purpose=SERVER_AUTH) for a client to use to verify aserver, and certificates for a server to use in verifying client certificates(purpose=CLIENT_AUTH). (Contributed by ChristianHeimes inbpo-19292.)

Two new windows-only functions,enum_certificates() andenum_crls() provide the ability to retrieve certificates,certificate information, and CRLs from the Windows cert store. (Contributedby Christian Heimes inbpo-17134.)

Support for server-side SNI (Server Name Indication) using the newssl.SSLContext.set_servername_callback() method.(Contributed by Daniel Black inbpo-8109.)

The dictionary returned bySSLSocket.getpeercert() contains additionalX509v3 extension items:crlDistributionPoints,calIssuers, andOCSP URIs. (Contributed by Christian Heimes inbpo-18379.)

stat¶

Thestat module is now backed by a C implementation in_stat. A Cimplementation is required as most of the values aren't standardized andare platform-dependent. (Contributed by Christian Heimes inbpo-11016.)

The module supports newST_MODE flags,S_IFDOOR,S_IFPORT, andS_IFWHT. (Contributed byChristian Hiemes inbpo-11016.)

struct¶

New functioniter_unpack and a newstruct.Struct.iter_unpack() method on compiled formats provide streamedunpacking of a buffer containing repeated instances of a given format of data.(Contributed by Antoine Pitrou inbpo-17804.)

subprocess¶

check_output() now accepts aninput argument that canbe used to provide the contents ofstdin for the command that is run.(Contributed by Zack Weinberg inbpo-16624.)

getstatus() andgetstatusoutput() nowwork on Windows. This change was actually inadvertently made in 3.3.4.(Contributed by Tim Golden inbpo-10197.)

sunau¶

Thegetparams() method now returns a namedtuple rather than aplain tuple. (Contributed by Claudiu Popa inbpo-18901.)

sunau.open() now supports the context management protocol: when used in awith block, theclose method of the returned object will becalled automatically at the end of the block. (Contributed by Serhiy Storchakainbpo-18878.)

AU_write.setsampwidth() now supports 24 bit samples, thus addingsupport for writing 24 sample using the module. (Contributed bySerhiy Storchaka inbpo-19261.)

Thewriteframesraw() andwriteframes() methods now accept anybytes-likeobject. (Contributed by Serhiy Storchaka inbpo-8311.)

sys¶

New functionsys.getallocatedblocks() returns the current number ofblocks allocated by the interpreter. (In CPython with the default--with-pymalloc setting, this is allocations made through thePyObject_Malloc() API.) This can be useful for tracking memory leaks,especially if automated via a test suite. (Contributed by Antoine Pitrouinbpo-13390.)

When the Python interpreter starts ininteractive mode, it checks for an__interactivehook__ attributeon thesys module. If the attribute exists, its value is called with noarguments just before interactive mode is started. The check is made after thePYTHONSTARTUP file is read, so it can be set there. Thesitemodulesets it to a function that enables tabcompletion and history saving (in~/.python-history) if the platformsupportsreadline. If you do not want this (new) behavior, you canoverride it inPYTHONSTARTUP,sitecustomize, orusercustomize by deleting this attribute fromsys (or setting itto some other callable). (Contributed by Éric Araujo and Antoine Pitrou inbpo-5845.)

tarfile¶

Thetarfile module now supports a simpleCommand-Line Interface whencalled as a script directly or via-m. This can be used to create andextract tarfile archives. (Contributed by Berker Peksag inbpo-13477.)

textwrap¶

TheTextWrapper class has two new attributes/constructorarguments:max_lines, which limits the number oflines in the output, andplaceholder, which is astring that will appear at the end of the output if it has been truncatedbecause ofmax_lines. Building on these capabilities, a new conveniencefunctionshorten() collapses all of the whitespace in the inputto single spaces and produces a single line of a givenwidth that ends withtheplaceholder (by default,[...]). (Contributed by Antoine Pitrou andSerhiy Storchaka inbpo-18585 andbpo-18725.)

threading¶

TheThread object representing the main thread can beobtained from the newmain_thread() function. In normalconditions this will be the thread from which the Python interpreter wasstarted. (Contributed by Andrew Svetlov inbpo-18882.)

traceback¶

A newtraceback.clear_frames() function takes a traceback objectand clears the local variables in all of the frames it references,reducing the amount of memory consumed. (Contributed by Andrew Kuchling inbpo-1565525.)

types¶

A newDynamicClassAttribute() descriptor provides a way to definean attribute that acts normally when looked up through an instance object, butwhich is routed to theclass__getattr__ when looked up through theclass. This allows one to have properties active on a class, and have virtualattributes on the class with the same name (seeEnum for an example).(Contributed by Ethan Furman inbpo-19030.)

urllib¶

urllib.request now supportsdata: URLs via theDataHandler class. (Contributed by Mathias Panzenböckinbpo-16423.)

The http method that will be used by aRequest classcan now be specified by setting amethodclass attribute on the subclass. (Contributed by Jason R Coombs inbpo-18978.)

Request objects are now reusable: if thefull_url ordataattributes are modified, all relevant internal properties are updated. Thismeans, for example, that it is now possible to use the sameRequest object in more than oneOpenerDirector.open() call with differentdata arguments, or tomodify aRequest'surl rather than recomputing itfrom scratch. There is also a newremove_header() method that can be used to removeheaders from aRequest. (Contributed by AlexeyKachayev inbpo-16464, Daniel Wozniak inbpo-17485, and Damien Brechtand Senthil Kumaran inbpo-17272.)

HTTPError objects now have aheaders attribute that provides access to theHTTP response headers associated with the error. (Contributed byBerker Peksag inbpo-15701.)

unittest¶

TheTestCase class has a new method,subTest(), that produces a context manager whosewith block becomes a "sub-test". This context manager allows a testmethod to dynamically generate subtests by, say, calling thesubTestcontext manager inside a loop. A single test method can thereby produce anindefinite number of separately identified and separately counted tests, all ofwhich will run even if one or more of them fail. For example:

classNumbersTest(unittest.TestCase):deftest_even(self):foriinrange(6):withself.subTest(i=i):self.assertEqual(i%2,0)

will result in six subtests, each identified in the unittest verbose outputwith a label consisting of the variable namei and a particular value forthat variable (i=0,i=1, etc). SeeDistinguishing test iterations using subtests for the fullversion of this example. (Contributed by Antoine Pitrou inbpo-16997.)

unittest.main() now accepts an iterable of test names fordefaultTest, where previously it only accepted a single test name as astring. (Contributed by Jyrki Pulliainen inbpo-15132.)

IfSkipTest is raised during test discovery (that is, at themodule level in the test file), it is now reported as a skip instead of anerror. (Contributed by Zach Ware inbpo-16935.)

discover() now sorts the discovered files to provideconsistent test ordering. (Contributed by Martin Melin and Jeff Ramnani inbpo-16709.)

TestSuite now drops references to tests as soon as the testhas been run, if the test is successful. On Python interpreters that dogarbage collection, this allows the tests to be garbage collected if nothingelse is holding a reference to the test. It is possible to override thisbehavior by creating aTestSuite subclass that defines acustom_removeTestAtIndex method. (Contributed by Tom Wardill, MattMcClure, and Andrew Svetlov inbpo-11798.)

A new test assertion context-manager,assertLogs(),will ensure that a given block of code emits a log message using thelogging module. By default the message can come from any logger andhave a priority ofINFO or higher, but both the logger name and analternative minimum logging level may be specified. The object returned by thecontext manager can be queried for theLogRecords and/orformatted messages that were logged. (Contributed by Antoine Pitrou inbpo-18937.)

Test discovery now works with namespace packages (Contributed by Claudiu Popainbpo-17457.)

unittest.mock objects now inspect their specification signatures whenmatching calls, which means an argument can now be matched by either positionor name, instead of only by position. (Contributed by Antoine Pitrou inbpo-17015.)

mock_open() objects now havereadline andreadlinesmethods. (Contributed by Toshio Kuratomi inbpo-17467.)

venv¶

venv now includes activation scripts for thecsh andfishshells. (Contributed by Andrew Svetlov inbpo-15417.)

EnvBuilder and thecreate() convenience functiontake a new keyword argumentwith_pip, which defaults toFalse, thatcontrols whether or notEnvBuilder ensures thatpip isinstalled in the virtual environment. (Contributed by Nick Coghlan inbpo-19552 as part of thePEP 453 implementation.)

wave¶

Thegetparams() method now returns a namedtuple rather than aplain tuple. (Contributed by Claudiu Popa inbpo-17487.)

wave.open() now supports the context management protocol. (Contributedby Claudiu Popa inbpo-17616.)

wave can nowwrite output to unseekable files. (Contributed by David Jones, Guilherme Polo, and SerhiyStorchaka inbpo-5202.)

Thewriteframesraw() andwriteframes() methods now accept anybytes-likeobject. (Contributed by Serhiy Storchaka inbpo-8311.)

weakref¶

NewWeakMethod class simulates weak references to boundmethods. (Contributed by Antoine Pitrou inbpo-14631.)

Newfinalize class makes it possible to register a callbackto be invoked when an object is garbage collected, without needing tocarefully manage the lifecycle of the weak reference itself. (Contributed byRichard Oudkerk inbpo-15528.)

The callback, if any, associated with aref is nowexposed via the__callback__ attribute. (Contributedby Mark Dickinson inbpo-17643.)

xml.etree¶

A new parser,XMLPullParser, allows anon-blocking applications to parse XML documents. An example can beseen atPull API for non-blocking parsing. (Contributed by AntoinePitrou inbpo-17741.)

Thexml.etree.ElementTreetostring() andtostringlist() functions, and theElementTreewrite() method, now have ashort_empty_elementskeyword-only parameterproviding control over whether elements with no content are written inabbreviated (<tag/>) or expanded (<tag></tag>) form. (Contributed byAriel Poliak and Serhiy Storchaka inbpo-14377.)

zipfile¶

Thewritepy() method of thePyZipFile class has a newfilterfunc option that can beused to control which directories and files are added to the archive. Forexample, this could be used to exclude test files from the archive.(Contributed by Christian Tismer inbpo-19274.)

TheallowZip64 parameter toZipFile andPyZipfile is nowTrue by default. (Contributed byWilliam Mallard inbpo-17201.)

PEP 445: Customization of CPython Memory Allocators¶

PEP 445 adds new C level interfaces to customize memory allocation inthe CPython interpreter.

PEP 442: Safe Object Finalization¶

PEP 442 removes the current limitations and quirks of object finalizationin CPython. With it, objects with__del__() methods, as well asgenerators withfinally clauses, can be finalized when they arepart of a reference cycle.

As part of this change, module globals are no longer forcibly set toNone during interpreter shutdown in most cases, instead relyingon the normal operation of the cyclic garbage collector. This avoids awhole class of interpreter-shutdown-time errors, usually involving__del__ methods, that have plagued Python since the cyclic GCwas first introduced.

PEP 456: Secure and Interchangeable Hash Algorithm¶

PEP 456 follows up on earlier security fix work done on Python's hashalgorithm to address certain DOS attacks to which public facing APIs backed bydictionary lookups may be subject. (Seebpo-14621 for the start of thecurrent round of improvements.) The PEP unifies CPython's hash code to make iteasier for a packager to substitute a different hash algorithm, and switchesPython's default implementation to a SipHash implementation on platforms thathave a 64 bit data type. Any performance differences in comparison with theolder FNV algorithm are trivial.

The PEP adds additional fields to thesys.hash_info named tuple todescribe the hash algorithm in use by the currently executing binary. Otherwise,the PEP does not alter any existing CPython APIs.

PEP 436: Argument Clinic¶

"Argument Clinic" (PEP 436) is now part of the CPython build processand can be used to simplify the process of defining and maintainingaccurate signatures for builtins and standard library extension modulesimplemented in C.

Some standard library extension modules have been converted to use ArgumentClinic in Python 3.4, andpydoc andinspect have been updatedaccordingly.

It is expected that signature metadata for programmatic introspection willbe added to additional callables implemented in C as part of Python 3.4maintenance releases.

其他建置和 C API 變更¶

• The newPyType_GetSlot() function has been added to the stable ABI,allowing retrieval of function pointers from named type slots when usingthe limited API. (Contributed by Martin von Löwis inbpo-17162.)

• The newPy_SetStandardStreamEncoding() pre-initialization APIallows applications embedding the CPython interpreter to reliably forcea particular encoding and error handler for the standard streams.(Contributed by Bastien Montagne and Nick Coghlan inbpo-16129.)

• Most Python C APIs that don't mutate string arguments are now correctlymarked as acceptingconstchar* rather thanchar*. (Contributedby Serhiy Storchaka inbpo-1772673.)

• A new shell version ofpython-config can be used even when a pythoninterpreter is not available (for example, in cross compilation scenarios).

• PyUnicode_FromFormat() now supports width and precisionspecifications for%s,%A,%U,%V,%S, and%R.(Contributed by Ysj Ray and Victor Stinner inbpo-7330.)

• New functionPyStructSequence_InitType2() supplements theexistingPyStructSequence_InitType() function. The differenceis that it returns0 on success and-1 on failure.

• The CPython source can now be compiled using the address sanity checkingfeatures of recent versions of GCC and clang: the false alarms in the smallobject allocator have been silenced. (Contributed by Dhiru Kholia inbpo-18596.)

• The Windows build now usesAddress Space Layout Randomization andData Execution Prevention. (Contributed byChristian Heimes inbpo-16632.)

• New functionPyObject_LengthHint() is the C API equivalentofoperator.length_hint(). (Contributed by Armin Ronacher inbpo-16148.)

其他改進¶

• Thepython command has a newoption,-I, which causes it to run in "isolated mode",which means thatsys.path contains neither the script's directory northe user'ssite-packages directory, and allPYTHON* environmentvariables are ignored (it implies both-s and-E). Otherrestrictions may also be applied in the future, with the goal being toisolate the execution of a script from the user's environment. This isappropriate, for example, when Python is used to run a system script. Onmost POSIX systems it can and should be used in the#! line of systemscripts. (Contributed by Christian Heimes inbpo-16499.)

• Tab-completion is now enabled by default in the interactive interpreteron systems that supportreadline. History is also enabled by default,and is written to (and read from) the file~/.python-history.(Contributed by Antoine Pitrou and Éric Araujo inbpo-5845.)

• Invoking the Python interpreter with--version now outputs the version tostandard output instead of standard error (bpo-18338). Similar changeswere made toargparse (bpo-18920) and other modules that havescript-like invocation capabilities (bpo-18922).

• The CPython Windows installer now adds.py to thePATHEXTvariable when extensions are registered, allowing users to run a pythonscript at the windows command prompt by just typing its name without the.py extension. (Contributed by Paul Moore inbpo-18569.)

• A newmake targetcoverage-reportwill build python, run the test suite, and generate an HTML coverage reportfor the C codebase usinggcov andlcov.

• python 迴歸測試套裝 的-R 選項現在也可以透過使用sys.getallocatedblocks() 來檢查記憶體配置洩漏。（由 Antoine Pitrou 在bpo-13390 貢獻。）

• python-m 現在可以使用於命名空間套件。

• Thestat module is now implemented in C, which means it gets thevalues for its constants from the C header files, instead of having thevalues hard-coded in the python module as was previously the case.

• Loading multiple python modules from a single OS module (.so,.dll)now works correctly (previously it silently returned the first pythonmodule in the file). (Contributed by Václav Šmilauer inbpo-16421.)

• A new opcode,LOAD_CLASSDEREF, has been added to fix a bug in theloading of free variables in class bodies that could be triggered by certainuses of__prepare__. (Contributed by Benjamin Peterson inbpo-17853.)

• A number of MemoryError-related crashes were identified and fixed by VictorStinner using hisPEP 445-basedpyfailmalloc tool (bpo-18408,bpo-18520).

• Thepyvenv command now accepts a--copies optionto use copies rather than symlinks even on systems where symlinks are thedefault. (Contributed by Vinay Sajip inbpo-18807.)

• Thepyvenv command also accepts a--without-pipoption to suppress the otherwise-automatic bootstrapping of pip intothe virtual environment. (Contributed by Nick Coghlan inbpo-19552as part of thePEP 453 implementation.)

• The encoding name is now optional in the value set for thePYTHONIOENCODING environment variable. This makes it possible toset just the error handler, without changing the default encoding.(Contributed by Serhiy Storchaka inbpo-18818.)

• Thebz2,lzma, andgzip moduleopen functions nowsupportx (exclusive creation) mode. (Contributed by Tim Heaney andVajrasky Kok inbpo-19201,bpo-19222, andbpo-19223.)

顯著最佳化¶

• The UTF-32 decoder is now 3x to 4x faster. (Contributed by Serhiy Storchakainbpo-14625.)

• The cost of hash collisions for sets is now reduced. Each hash tableprobe now checks a series of consecutive, adjacent key/hash pairs beforecontinuing to make random probes through the hash table. This exploitscache locality to make collision resolution less expensive.The collision resolution scheme can be described as a hybrid of linearprobing and open addressing. The number of additional linear probesdefaults to nine. This can be changed at compile-time by definingLINEAR_PROBES to be any value. Set LINEAR_PROBES=0 to turn-offlinear probing entirely. (Contributed by Raymond Hettinger inbpo-18771.)

• The interpreter starts about 30% faster. A couple of measures lead to thespeedup. The interpreter loads fewer modules on startup, e.g. there,collections andlocale modules and their dependencies are nolonger imported by default. The marshal module has been improved to loadcompiled Python code faster. (Contributed by Antoine Pitrou, ChristianHeimes and Victor Stinner inbpo-19219,bpo-19218,bpo-19209,bpo-19205 andbpo-9548.)

• bz2.BZ2File is now as fast or faster than the Python2 version formost cases.lzma.LZMAFile has also been optimized. (Contributed bySerhiy Storchaka and Nadeem Vawda inbpo-16034.)

• random.getrandbits() is 20%-40% faster for small integers (the mostcommon use case). (Contributed by Serhiy Storchaka inbpo-16674.)

• By taking advantage of the new storage format for strings, pickling ofstrings is now significantly faster. (Contributed by Victor Stinner andAntoine Pitrou inbpo-15596.)

• A performance issue inio.FileIO.readall() has been solved. Thisparticularly affects Windows, and significantly speeds up the case of pipingsignificant amounts of data throughsubprocess. (Contributedby Richard Oudkerk inbpo-15758.)

• html.escape() is now 10x faster. (Contributed by Matt Bryant inbpo-18020.)

• On Windows, the nativeVirtualAlloc is now used instead of the CRTmalloc inobmalloc. Artificial benchmarks show about a 3% memorysavings.

• os.urandom() now uses a lazily opened persistent file descriptorso as to avoid using many file descriptors when run in parallel frommultiple threads. (Contributed by Antoine Pitrou inbpo-18756.)

已棄用的 Python API¶

• As mentioned inPEP 451：用於引入系統的 ModuleSpec 型別, a number ofimportlibmethods and functions are deprecated:importlib.find_loader() isreplaced byimportlib.util.find_spec();importlib.machinery.PathFinder.find_module() is replaced byimportlib.machinery.PathFinder.find_spec();importlib.abc.MetaPathFinder.find_module() is replaced byimportlib.abc.MetaPathFinder.find_spec();importlib.abc.PathEntryFinder.find_loader() andfind_module() are replaced byimportlib.abc.PathEntryFinder.find_spec(); all of thexxxLoader ABCload_module methods (importlib.abc.Loader.load_module(),importlib.abc.InspectLoader.load_module(),importlib.abc.FileLoader.load_module(),importlib.abc.SourceLoader.load_module()) should no longer beimplemented, instead loaders should implement anexec_module method(importlib.abc.Loader.exec_module(),importlib.abc.InspectLoader.exec_module()importlib.abc.SourceLoader.exec_module()) and let the import systemtake care of the rest; andimportlib.abc.Loader.module_repr(),importlib.util.module_for_loader(),importlib.util.set_loader(),andimportlib.util.set_package() are no longer needed because theirfunctions are now handled automatically by the import system.

• Theimp module is pending deprecation. To keep compatibility withPython 2/3 code bases, the module's removal is currently not scheduled.

• Theformatter module is pending deprecation and is slated for removalin Python 3.6.

• MD5 as the defaultdigestmod for thehmac.new() function isdeprecated. Python 3.6 will require an explicit digest name or constructor asdigestmod argument.

• The internalNetrc class in theftplib module has been documentedas deprecated in its docstring for quite some time. It now emits aDeprecationWarning and will be removed completely in Python 3.5.

• The undocumentedendtime argument tosubprocess.Popen.wait() shouldnot have been exposed and is hopefully not in use; it is deprecated andwill mostly likely be removed in Python 3.5.

• Thestrict argument ofHTMLParser is deprecated.

• TheplistlibreadPlist(),writePlist(),readPlistFromBytes(), andwritePlistToBytes() functions are deprecated in favor of thecorresponding new functionsload(),dump(),loads(), anddumps().Data()is deprecated in favor of just using thebytes constructor.

• Thesysconfig keySO is deprecated, it has been replaced byEXT_SUFFIX.

• TheU mode accepted by variousopen functions is deprecated.In Python3 it does not do anything useful, and should be replaced byappropriate uses ofio.TextIOWrapper (if needed) and itsnewlineargument.

• Theparser argument ofxml.etree.ElementTree.iterparse() hasbeen deprecated, as has thehtml argument ofXMLParser(). To prepare for the removal of thelatter, all arguments toXMLParser should be passed by keyword.

已棄用功能¶

• RunningIDLE --- Python 編輯器與 shell with the-n flag (no subprocess) is deprecated.However, the feature will not be removed untilbpo-18823 is resolved.

• The site module adding a "site-python" directory to sys.path, if itexists, is deprecated (bpo-19375).

不再支援的作業系統¶

Support for the following operating systems has been removed from the sourceand build tools:

• OS/2 (bpo-16135)。

• Windows 2000 (changeset e52df05b496a).

• Windows systems whereCOMSPEC points tocommand.com (bpo-14470).

• VMS (bpo-16136)。

API 與功能的移除¶

The following obsolete and previously deprecated APIs and features have beenremoved:

• The unmaintainedMisc/TextMate andMisc/vim directories have beenremoved (see thedevguidefor suggestions on what to use instead).

• TheSO makefile macro is removed (it was replaced by theSHLIB_SUFFIX andEXT_SUFFIX macros) (bpo-16754).

• ThePyThreadState.tick_counter field has been removed; its value hasbeen meaningless since Python 3.2, when the "new GIL" was introduced(bpo-19199).

• PyLoader andPyPycLoader have been removed fromimportlib.(Contributed by Taras Lyapun inbpo-15641.)

• Thestrict argument toHTTPConnection andHTTPSConnection has been removed. HTTP 0.9-style"Simple Responses" are no longer supported.

• The deprecatedurllib.request.Request getter and setter methodsadd_data,has_data,get_data,get_type,get_host,get_selector,set_proxy,get_origin_req_host, andis_unverifiable have been removed (use direct attribute access instead).

• Support for loading the deprecatedTYPE_INT64 has been removed frommarshal. (Contributed by Dan Riti inbpo-15480.)

• inspect.Signature: positional-only parameters are now requiredto have a valid name.

• object.__format__() no longer accepts non-empty format strings, it nowraises aTypeError instead. Using a non-empty string has beendeprecated since Python 3.2. This change has been made to prevent asituation where previously working (but incorrect) code would start failingif an object gained a __format__ method, which means that your code may nowraise aTypeError if you are using an's' format code with objectsthat do not have a __format__ method that handles it. Seebpo-7994 forbackground.

• difflib.SequenceMatcher.isbjunk() anddifflib.SequenceMatcher.isbpopular() were deprecated in 3.2, and havenow been removed: usexinsm.bjunk andxinsm.bpopular, wheresm is aSequenceMatcher object(bpo-13248).

程式碼的清除¶

• The unused and undocumented internalScanner class has been removed fromthepydoc module.

• The private and effectively unused_gestalt module has been removed,along with the privateplatform functions_mac_ver_lookup,_mac_ver_gstalt, and_bcd2str, which would only have ever been calledon badly broken OSX systems (seebpo-18393).

• The hardcoded copies of certainstat constants that were included inthetarfile module namespace have been removed.

Changes in 'python' Command Behavior¶

• In a posix shell, setting thePATH environment variable toan empty value is equivalent to not setting it at all. However, settingPYTHONPATH to an empty value wasnot equivalent to not setting itat all: settingPYTHONPATH to an empty value was equivalent tosetting it to., which leads to confusion when reasoning by analogy tohowPATH works. The behavior now conforms to the posix conventionforPATH.

• The [X refs, Y blocks] output of a debug (--with-pydebug) build of theCPython interpreter is now off by default. It can be re-enabled using the-Xshowrefcount option. (Contributed by Ezio Melotti inbpo-17323.)

• The python command and most stdlib scripts (as well asargparse) nowoutput--version information tostdout instead ofstderr (forissue list see其他改進 above).

Python API 的變更¶

• The ABCs defined inimportlib.abc now either raise the appropriateexception or return a default value instead of raisingNotImplementedError blindly. This will only affect code callingsuper() and falling through all the way to the ABCs. For compatibility,catch bothNotImplementedError or the appropriate exception as needed.

• The module type now initializes the__package__ and__loader__attributes toNone by default. To determine if these attributes were setin a backwards-compatible fashion, use e.g.getattr(module,'__loader__',None)isnotNone. (bpo-17115.)

• importlib.util.module_for_loader() now sets__loader__ and__package__ unconditionally to properly support reloading. If this is notdesired then you will need to set these attributes manually. You can useimportlib.util.module_to_load() for module management.

• Import now resets relevant attributes (e.g.__name__,__loader__,__package__,__file__,__cached__) unconditionally when reloading.Note that this restores a pre-3.3 behavior in that it means a module isre-found when re-loaded (bpo-19413).

• Frozen packages no longer set__path__ to a list containing the packagename, they now set it to an empty list. The previous behavior could causethe import system to do the wrong thing on submodule imports if there wasalso a directory with the same name as the frozen package. The correct wayto determine if a module is a package or not is to usehasattr(module,'__path__') (bpo-18065).

• Frozen modules no longer define a__file__ attribute. It's semanticallyincorrect for frozen modules to set the attribute as they are not loaded fromany explicit location. If you must know that a module comes from frozen codethen you can see if the module's__spec__.location is set to'frozen',check if the loader is a subclass ofimportlib.machinery.FrozenImporter,or if Python 2 compatibility is necessary you can useimp.is_frozen().

• py_compile.compile() now raisesFileExistsError if the file pathit would write to is a symlink or a non-regular file. This is to act as awarning that import will overwrite those files with a regular file regardlessof what type of file path they were originally.

• importlib.abc.SourceLoader.get_source() no longer raisesImportError when the source code being loaded triggers aSyntaxError orUnicodeDecodeError. AsImportError ismeant to be raised only when source code cannot be found but it should, it wasfelt to be over-reaching/overloading of that meaning when the source code isfound but improperly structured. If you were catching ImportError before andwish to continue to ignore syntax or decoding issues, catch all threeexceptions now.

• functools.update_wrapper() andfunctools.wraps() now correctlyset the__wrapped__ attribute to the function being wrapped, even ifthat function also had its__wrapped__ attribute set. This means__wrapped__ attributes now correctly link a stack of decoratedfunctions rather than every__wrapped__ attribute in the chainreferring to the innermost function. Introspection libraries thatassumed the previous behaviour was intentional can useinspect.unwrap() to access the first function in the chain that hasno__wrapped__ attribute.

• inspect.getfullargspec() has been reimplemented on top ofinspect.signature() and hence handles a much wider variety of callableobjects than it did in the past. It is expected that additional builtin andextension module callables will gain signature metadata over the course ofthe Python 3.4 series. Code that assumes thatinspect.getfullargspec() will fail on non-Python callables may needto be adjusted accordingly.

• importlib.machinery.PathFinder now passes on the current workingdirectory to objects insys.path_hooks for the empty string. Thisresults insys.path_importer_cache never containing'', thusiterating throughsys.path_importer_cache based onsys.pathwill not find all keys. A module's__file__ when imported in the currentworking directory will also now have an absolute path, including when using-m with the interpreter (except for__main__.__file__ when a scripthas been executed directly using a relative path) (Contributed by BrettCannon inbpo-18416). is specified on the command-line)(bpo-18416).

• The removal of thestrict argument toHTTPConnectionandHTTPSConnection changes the meaning of theremaining arguments if you are specifying them positionally rather than bykeyword. If you've been paying attention to deprecation warnings your codeshould already be specifying any additional arguments via keywords.

• Strings betweenfrom__future__import... statements nowalways raiseaSyntaxError. Previously if there was no leading docstring, aninterstitial string would sometimes be ignored. This brings CPython intocompliance with the language spec; Jython and PyPy already were.(bpo-17434).

• ssl.SSLSocket.getpeercert() andssl.SSLSocket.do_handshake()now raise anOSError withENOTCONN when theSSLSocket is notconnected, instead of the previous behavior of raising anAttributeError. In addition,getpeercert()will raise aValueError if the handshake has not yet been done.

• base64.b32decode() now raises abinascii.Error when theinput string contains non-b32-alphabet characters, instead of aTypeError. This particularTypeError was missed when the otherTypeErrors were converted. (Contributed by Serhiy Storchaka inbpo-18011.) Note: this change was also inadvertently applied in Python3.3.3.

• Thefile attribute is now automatically closed whenthe creatingcgi.FieldStorage instance is garbage collected. If youwere pulling the file object out separately from thecgi.FieldStorageinstance and not keeping the instance alive, then you should either store theentirecgi.FieldStorage instance or read the contents of the filebefore thecgi.FieldStorage instance is garbage collected.

• Callingread orwrite on a closed SSL socket now raises aninformativeValueError rather than the previous more mysteriousAttributeError (bpo-9177).

• slice.indices() no longer produces anOverflowError for hugevalues. As a consequence of this fix,slice.indices() now raises aValueError if given a negative length; previously it returned nonsensevalues (bpo-14794).

• Thecomplex constructor, unlike thecmath functions, wasincorrectly acceptingfloat values if an object's__complex__special method returned one. This now raises aTypeError.(bpo-16290.)

• Theint constructor in 3.2 and 3.3 erroneously acceptsfloatvalues for thebase parameter. It is unlikely anyone was doing this, butif so, it will now raise aTypeError (bpo-16772).

• Defaults for keyword-only arguments are now evaluatedafter defaults forregular keyword arguments, instead of before. Hopefully no one wrote anycode that depends on the previous buggy behavior (bpo-16967).

• Stale thread states are now cleared afterfork(). This may causesome system resources to be released that previously were incorrectly keptperpetually alive (for example, database connections kept in thread-localstorage). (bpo-17094.)

• Parameter names in__annotations__ dicts are now mangled properly,similarly to__kwdefaults__.(Contributed by Yury Selivanov inbpo-20625.)

• hashlib.hash.name now always returns the identifier in lower case.Previously some builtin hashes had uppercase names, but now that it is aformal public interface the naming has been made consistent (bpo-18532).

• Becauseunittest.TestSuite now drops references to tests after theyare run, test harnesses that reuse aTestSuite to re-runa set of tests may fail. Test suites should not be re-used in this fashionsince it means state is retained between test runs, breaking the testisolation thatunittest is designed to provide. However, if the lackof isolation is considered acceptable, the old behavior can be restored bycreating aTestSuite subclass that defines a_removeTestAtIndex method that does nothing (seeTestSuite.__iter__()) (bpo-11798).

• unittest now usesargparse for command line parsing. There arecertain invalid command forms that used to work that are no longer allowed;in theory this should not cause backward compatibility issues since thedisallowed command forms didn't make any sense and are unlikely to be in use.

• There.split(),re.findall(), andre.sub() functions, andthegroup() andgroups() methods ofmatch objects now always return abytes object when the stringto be matched is abytes-like object. Previously the return typematched the input type, so if your code was depending on the return valuebeing, say, abytearray, you will need to change your code.

• audioop functions now raise an error immediately if passed stringinput, instead of failing randomly later on (bpo-16685).

• The newconvert_charrefs argument toHTMLParsercurrently defaults toFalse for backward compatibility, but willeventually be changed to default toTrue. It is recommended that you addthis keyword, with the appropriate value, to anyHTMLParser calls in your code (bpo-13633).

• Since thedigestmod argument to thehmac.new() function will in thefuture have no default, all calls tohmac.new() should be changed toexplicitly specify adigestmod (bpo-17276).

• Callingsysconfig.get_config_var() with theSO key, or lookingSO up in the results of a call tosysconfig.get_config_vars()is deprecated. This key should be replaced byEXT_SUFFIX orSHLIB_SUFFIX, depending on the context (bpo-19555).

• Any calls toopen functions that specifyU should be modified.U is ineffective in Python3 and will eventually raise an error if used.Depending on the function, the equivalent of its old Python2 behavior can beachieved using either anewline argument, or if necessary by wrapping thestream inTextIOWrapper to use itsnewline argument(bpo-15204).

• If you usepyvenv in a script and desire that pipnot be installed, you must add--without-pip to your commandinvocation.

• The default behavior ofjson.dump() andjson.dumps() whenan indent is specified has changed: it no longer produces trailingspaces after the item separating commas at the ends of lines. Thiswill matter only if you have tests that are doing white-space-sensitivecomparisons of such output (bpo-16333).

• doctest now looks for doctests in extension module__doc__strings, so if your doctest test discovery includes extension modules thathave things that look like doctests in them you may see test failures you'venever seen before when running your tests (bpo-3158).

• Thecollections.abc module has been slightly refactored aspart of the Python startup improvements. As a consequence of this, it is nolonger the case that importingcollections automatically importscollections.abc. If your program depended on the (undocumented)implicit import, you will need to add an explicitimportcollections.abc(bpo-20784).

C API 中的改動¶

• PyEval_EvalFrameEx(),PyObject_Repr(), andPyObject_Str(), along with some other internal C APIs, now includea debugging assertion that ensures they are not used in situations wherethey may silently discard a currently active exception. In cases wherediscarding the active exception is expected and desired (for example,because it has already been saved locally withPyErr_Fetch() oris being deliberately replaced with a different exception), an explicitPyErr_Clear() call will be needed to avoid triggering theassertion when invoking these operations (directly or indirectly) andrunning against a version of Python that is compiled with assertionsenabled.

• PyErr_SetImportError() now setsTypeError when itsmsgargument is not set. Previously onlyNULL was returned with no exceptionset.

• The result of thePyOS_ReadlineFunctionPointer callback mustnow be a string allocated byPyMem_RawMalloc() orPyMem_RawRealloc(), orNULL if an error occurred, instead of astring allocated byPyMem_Malloc() orPyMem_Realloc()(bpo-16742)

• PyThread_set_key_value() now always set the value. In Python3.3, the function did nothing if the key already exists (if the currentvalue is a non-NULL pointer).

• Thef_tstate (thread state) field of thePyFrameObjectstructure has been removed to fix a bug: seebpo-14432 for therationale.

PEP 476: Enabling certificate verification by default for stdlib http clients¶

http.client and modules which use it, such asurllib.request andxmlrpc.client, will now verify that the server presents a certificatewhich is signed by a CA in the platform trust store and whose hostname matchesthe hostname being requested by default, significantly improving security formany applications.

For applications which require the old previous behavior, they can pass analternate context:

importurllib.requestimportssl# This disables all verificationcontext=ssl._create_unverified_context()# This allows using a specific certificate for the host, which doesn't need# to be in the trust storecontext=ssl.create_default_context(cafile="/path/to/file.crt")urllib.request.urlopen("https://invalid-cert",context=context)