
What's New In Python 3.5
************************

Release:
   3.5.0

Date:
   September 13, 2015

Editors:
   Elvis Pranskevichus <elprans@gmail.com>, Yury Selivanov
   <yselivanov@gmail.com>

Python 3.5 was released on September 13, 2015.

This article explains the new features in Python 3.5, compared to 3.4.
For full details, see the changelog.

See also: **PEP 478** - Python 3.5 Release Schedule


Summary -- Release highlights
=============================

New syntax features:

* **PEP 492**, coroutines with async and await syntax.

* **PEP 465**, a new matrix multiplication operator: "a @ b".

* **PEP 448**, additional unpacking generalizations.

New library modules:

* "zipapp": *Improving Python ZIP Application Support* (**PEP
  441**).

New built-in features:

* "bytes % args", "bytearray % args": **PEP 461** - Adding "%"
  formatting to bytes and bytearray.

* "b'\xf0\x9f\x90\x8d'.hex()",
  "bytearray(b'\xf0\x9f\x90\x8d').hex()",
  "memoryview(b'\xf0\x9f\x90\x8d').hex()": issue 9951 - A "hex" method
  has been added to bytes, bytearray, and memoryview.

* "memoryview" (including multi-dimensional) now supports tuple
  indexing. (Contributed by Antoine Pitrou in issue 23632.)

* Generators have new "gi_yieldfrom" attribute, which returns the
  object being iterated by "yield from" expressions. (Contributed by
  Benno Leslie and Yury Selivanov in issue 24450.)

* New "RecursionError" exception.  (Contributed by Georg Brandl in
  issue 19235.)

* New "StopAsyncIteration" exception.  (Contributed by Yury
  Selivanov in issue 24017.  See also **PEP 492**.)

CPython implementation improvements:

* When the "LC_TYPE" locale is the POSIX locale ("C" locale),
  "sys.stdin" and "sys.stdout" are now using the "surrogateescape"
  error handler, instead of the "strict" error handler. (Contributed
  by Victor Stinner in issue 19977.)

* ".pyo" files are no longer used and have been replaced by a more
  flexible scheme that inclides the optimization level explicitly in
  ".pyc" name. (**PEP 488**)

* Builtin and extension modules are now initialized in a multi-phase
  process, which is similar to how Python modules are loaded. (**PEP
  489**).

Significantly Improved Library Modules:

* "collections.OrderedDict" is now implemented in C, which makes it
  4 to 100 times faster.  (Contributed by Eric Snow in issue 16991.)

* You may now pass bytes to the "tempfile" module's APIs and it will
  return the temporary pathname as "bytes" instead of "str". It also
  accepts a value of "None" on parameters where only str was accepted
  in the past to do the right thing based on the types of the other
  inputs.  Two functions, "gettempdirb()" and "gettempprefixb()", have
  been added to go along with this. This behavior matches that of the
  "os" APIs. (Contributed by Gregory P. Smith in issue 24230.)

* "ssl" module gained support for Memory BIO, which decouples SSL
  protocol handling from network IO.  (Contributed by Geert Jansen in
  issue 21965.)

* "traceback" has new lightweight and convenient to work with
  classes "TracebackException", "StackSummary", and "FrameSummary".
  (Contributed by Robert Collins in issue 17911.)

* Most of "functools.lru_cache()" machinery is now implemented in C.
  (Contributed by Matt Joiner, Alexey Kachayev, and Serhiy Storchaka
  in issue 14373.)

Security improvements:

* SSLv3 is now disabled throughout the standard library. It can
  still be enabled by instantiating a "ssl.SSLContext" manually.  (See
  issue 22638 for more details; this change was backported to CPython
  3.4 and 2.7.)

* HTTP cookie parsing is now stricter, in order to protect against
  potential injection attacks. (Contributed by Antoine Pitrou in issue
  22796.)

Windows improvements:

* A new installer for Windows has replaced the old MSI. See *Using
  Python on Windows* for more information.

* Windows builds now use Microsoft Visual C++ 14.0, and extension
  modules should use the same.

Please read on for a comprehensive list of user-facing changes,
including many other smaller improvements, CPython optimizations,
deprecations, and potential porting issues.


New Features
============


PEP 492 - Coroutines with async and await syntax
------------------------------------------------

**PEP 492** greatly improves support for asynchronous programming in
Python by adding *awaitable objects*, *coroutine functions*,
*asynchronous iteration*, and *asynchronous context managers*.

Coroutine functions are declared using the new "async def" syntax:

   >>> async def coro():
   ...     return 'spam'

Inside a coroutine function, the new "await" expression can be used to
suspend coroutine execution until the result is available.  Any object
can be *awaited*, as long as it implements the *awaitable* protocol by
defining the "__await__()" method.

PEP 492 also adds "async for" statement for convenient iteration over
asynchronous iterables.

An example of a simple HTTP client written using the new syntax:

   import asyncio

   async def http_get(domain):
       reader, writer = await asyncio.open_connection(domain, 80)

       writer.write(b'\r\n'.join([
           b'GET / HTTP/1.1',
           b'Host: %b' % domain.encode('latin-1'),
           b'Connection: close',
           b'', b''
       ]))

       async for line in reader:
           print('>>>', line)

       writer.close()

   loop = asyncio.get_event_loop()
   try:
       loop.run_until_complete(http_get('example.com'))
   finally:
       loop.close()

Similarly to asynchronous iteration, there is a new syntax for
asynchronous context managers.  The following script:

   import asyncio

   async def coro(name, lock):
       print('coro {}: waiting for lock'.format(name))
       async with lock:
           print('coro {}: holding the lock'.format(name))
           await asyncio.sleep(1)
           print('coro {}: releasing the lock'.format(name))

   loop = asyncio.get_event_loop()
   lock = asyncio.Lock()
   coros = asyncio.gather(coro(1, lock), coro(2, lock))
   try:
       loop.run_until_complete(coros)
   finally:
       loop.close()

will print:

   coro 2: waiting for lock
   coro 2: holding the lock
   coro 1: waiting for lock
   coro 2: releasing the lock
   coro 1: holding the lock
   coro 1: releasing the lock

Note that both "async for" and "async with" can only be used inside a
coroutine function declared with "async def".

Coroutine functions are intended to be run inside a compatible event
loop, such as "asyncio.Loop".

See also: **PEP 492** -- Coroutines with async and await syntax

     PEP written and implemented by Yury Selivanov.


PEP 465 - A dedicated infix operator for matrix multiplication
--------------------------------------------------------------

**PEP 465** adds the "@" infix operator for matrix multiplication.
Currently, no builtin Python types implement the new operator,
however, it can be implemented by defining "__matmul__()",
"__rmatmul__()", and "__imatmul__()" for regular, reflected, and in-
place matrix multiplication.  The semantics of these methods is
similar to that of methods defining other infix arithmetic operators.

Matrix multiplication is a notably common operation in many fields of
mathematics, science, engineering, and the addition of "@" allows
writing cleaner code:

   S = (H @ beta - r).T @ inv(H @ V @ H.T) @ (H @ beta - r)

instead of:

   S = dot((dot(H, beta) - r).T,
           dot(inv(dot(dot(H, V), H.T)), dot(H, beta) - r))

An upcoming release of NumPy 1.10 will add support for the new
operator:

   >>> import numpy

   >>> x = numpy.ones(3)
   >>> x
   array([ 1., 1., 1.])

   >>> m = numpy.eye(3)
   >>> m
   array([[ 1., 0., 0.],
          [ 0., 1., 0.],
          [ 0., 0., 1.]])

   >>> x @ m
   array([ 1., 1., 1.])

See also: **PEP 465** -- A dedicated infix operator for matrix
  multiplication

     PEP written by Nathaniel J. Smith; implemented by Benjamin
     Peterson.


PEP 448 - Additional Unpacking Generalizations
----------------------------------------------

**PEP 448** extends the allowed uses of the "*" iterable unpacking
operator and "**" dictionary unpacking operator.  It is now possible
to use an arbitrary number of unpackings in function calls:

   >>> print(*[1], *[2], 3, *[4, 5])
   1 2 3 4 5

   >>> def fn(a, b, c, d):
   ...     print(a, b, c, d)
   ...

   >>> fn(**{'a': 1, 'c': 3}, **{'b': 2, 'd': 4})
   1 2 3 4

Similarly, tuple, list, set, and dictionary displays allow multiple
unpackings:

   >>> *range(4), 4
   (0, 1, 2, 3, 4)

   >>> [*range(4), 4]
   [0, 1, 2, 3, 4]

   >>> {*range(4), 4, *(5, 6, 7)}
   {0, 1, 2, 3, 4, 5, 6, 7}

   >>> {'x': 1, **{'y': 2}}
   {'x': 1, 'y': 2}

See also: **PEP 448** -- Additional Unpacking Generalizations

     PEP written by Joshua Landau; implemented by Neil Girdhar, Thomas
     Wouters, and Joshua Landau.


PEP 461 - % formatting support for bytes and bytearray
------------------------------------------------------

PEP 461 adds % formatting to "bytes" and "bytearray", aiding in
handling data that is a mixture of binary and ASCII compatible text.
This feature also eases porting such code from Python 2.

Examples:

   >>> b'Hello %s!' % b'World'
   b'Hello World!'

   >>> b'x=%i y=%f' % (1, 2.5)
   b'x=1 y=2.500000'

Unicode is not allowed for "%s", but it is accepted by "%a"
(equivalent of "repr(obj).encode('ascii', 'backslashreplace')"):

   >>> b'Hello %s!' % 'World'
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: %b requires bytes, or an object that implements __bytes__, not 'str'

   >>> b'price: %a' % '10€'
   b"price: '10\\u20ac'"

See also: **PEP 461** -- Adding % formatting to bytes and bytearray

     PEP written by Ethan Furman; implemented by Neil Schemenauer and
     Ethan Furman.


PEP 484 - Type Hints
--------------------

This PEP introduces a provisional module to provide these standard
definitions and tools, along with some conventions for situations
where annotations are not available.

For example, here is a simple function whose argument and return type
are declared in the annotations:

   def greeting(name: str) -> str:
       return 'Hello ' + name

The type system supports unions, generic types, and a special type
named "Any" which is consistent with (i.e. assignable to and from) all
types.

See also: * "typing" module documentation


  * **PEP 484** -- Type Hints

       PEP written by Guido van Rossum, Jukka Lehtosalo, and Łukasz
       Langa; implemented by Guido van Rossum.


PEP 471 - os.scandir() function -- a better and faster directory iterator
-------------------------------------------------------------------------

**PEP 471** adds a new directory iteration function, "os.scandir()",
to the standard library.  Additionally, "os.walk()" is now implemented
using "os.scandir()", which speeds it up by 3-5 times on POSIX systems
and by 7-20 times on Windows systems.

See also: **PEP 471** -- os.scandir() function -- a better and
  faster directory iterator

     PEP written and implemented by Ben Hoyt with the help of Victor
     Stinner.


PEP 475: Retry system calls failing with EINTR
----------------------------------------------

**PEP 475** adds support for automatic retry of system calls failing
with "EINTR": this means that user code doesn't have to deal with
EINTR or "InterruptedError" manually, and should make it more robust
against asynchronous signal reception.

Examples of functions which are now retried when interrupted by a
signal instead of raising "InterruptedError" if the Python signal
handler does not raise an exception:

* "open()", "os.open()", "io.open()";

* functions of the "faulthandler" module;

* "os" functions: "fchdir()", "fchmod()", "fchown()", "fdatasync()",
  "fstat()", "fstatvfs()", "fsync()", "ftruncate()", "mkfifo()",
  "mknod()", "posix_fadvise()", "posix_fallocate()", "pread()",
  "pwrite()", "read()", "readv()", "sendfile()", "wait3()", "wait4()",
  "wait()", "waitid()", "waitpid()", "write()", "writev()";

* special cases: "os.close()" and "os.dup2()" now ignore "EINTR"
  error, the syscall is not retried (see the PEP for the rationale);

* "select" functions: "poll()", "poll()", "control()", "poll()",
  "select()";

* "socket.socket()" methods: "accept()", "connect()" (except for
  non- blocking sockets), "recv()", "recvfrom()", "recvmsg()",
  "send()", "sendall()", "sendmsg()", "sendto()";

* "signal.sigtimedwait()", "signal.sigwaitinfo()";

* "time.sleep()".

See also: **PEP 475** -- Retry system calls failing with EINTR

     PEP and implementation written by Charles-François Natali and
     Victor Stinner, with the help of Antoine Pitrou (the french
     connection).


PEP 479: Change StopIteration handling inside generators
--------------------------------------------------------

**PEP 479** changes the behavior of generators: when a "StopIteration"
exception is raised inside a generator, it is replaced with a
"RuntimeError".  To enable the feature a "__future__" import should be
used:

   from __future__ import generator_stop

Without a "__future__" import, a "PendingDeprecationWarning" will be
raised.

See also: **PEP 479** -- Change StopIteration handling inside
  generators

     PEP written by Chris Angelico and Guido van Rossum. Implemented
     by Chris Angelico, Yury Selivanov and Nick Coghlan.


PEP 486: Make the Python Launcher aware of virtual environments
---------------------------------------------------------------

**PEP 486** makes the Windows launcher (see **PEP 397**) aware of an
active virtual environment. When the default interpreter would be used
and the "VIRTUAL_ENV" environment variable is set, the interpreter in
the virtual environment will be used.

See also: **PEP 486** -- Make the Python Launcher aware of virtual
  environments

     PEP written and implemented by Paul Moore.


PEP 488: Elimination of PYO files
---------------------------------

**PEP 488** does away with the concept of ".pyo" files. This means
that ".pyc" files represent both unoptimized and optimized bytecode.
To prevent the need to constantly regenerate bytecode files, ".pyc"
files now have an optional "opt-" tag in their name when the bytecode
is optimized. This has the side-effect of no more bytecode file name
clashes when running under either *-O* or *-OO*. Consequently,
bytecode files generated from *-O*, and *-OO* may now exist
simultaneously. "importlib.util.cache_from_source()" has an updated
API to help with this change.

See also: **PEP 488** -- Elimination of PYO files

     PEP written and implemented by Brett Cannon.


PEP 489: Multi-phase extension module initialization
----------------------------------------------------

**PEP 489** updates extension module initialization to take advantage
of the two step module loading mechanism introduced by **PEP 451** in
Python 3.4.

This change brings the import semantics of extension modules that opt-
in to using the new mechanism much closer to those of Python source
and bytecode modules, including the ability to use any valid
identifier as a module name, rather than being restricted to ASCII.

See also: **PEP 489** -- Multi-phase extension module initialization

     PEP written by Petr Viktorin, Stefan Behnel, and Nick Coghlan;
     implemented by Petr Viktorin.


PEP 485: A function for testing approximate equality
----------------------------------------------------

**PEP 485** adds the "math.isclose()" and "cmath.isclose()" functions
which tell whether two values are approximately equal or "close" to
each other.  Whether or not two values are considered close is
determined according to given absolute and relative tolerances.

See also: **PEP 485** -- A function for testing approximate equality

     PEP written by Christopher Barker; implemented by Chris Barker
     and Tal Einat.


Other Language Changes
======================

Some smaller changes made to the core Python language are:

* Added the ""namereplace"" error handlers.  The
  ""backslashreplace"" error handlers now works with decoding and
  translating. (Contributed by Serhiy Storchaka in issue 19676 and
  issue 22286.)

* The *-b* option now affects comparisons of "bytes" with "int".
  (Contributed by Serhiy Storchaka in issue 23681.)

* New Kazakh *codec* "kz1048".  (Contributed by Serhiy Storchaka in
  issue 22682.)

* Property docstrings are now writable. This is especially useful
  for "collections.namedtuple()" docstrings. (Contributed by Berker
  Peksag in issue 24064.)

* New Tajik *codec* "koi8_t".  (Contributed by Serhiy Storchaka in
  issue 22681.)

* Circular imports involving relative imports are now supported.
  (Contributed by Brett Cannon and Antoine Pitrou in issue 17636.)


New Modules
===========


zipapp
------

The new "zipapp" module (specified in **PEP 441**) provides an API and
command line tool for creating executable Python Zip Applications,
which were introduced in Python 2.6 in issue 1739468, but which were
not well publicized, either at the time or since.

With the new module, bundling your application is as simple as putting
all the files, including a "__main__.py" file, into a directory
"myapp" and running:

   $ python -m zipapp myapp
   $ python myapp.pyz

The module implementation has been contributed by Paul Moore in issue
23491.

See also: **PEP 441** -- Improving Python ZIP Application Support


Improved Modules
================


argparse
--------

The "ArgumentParser" class now allows to disable *abbreviated usage*
of long options by setting *allow_abbrev* to "False".  (Contributed by
Jonathan Paugh, Steven Bethard, paul j3 and Daniel Eriksson in issue
14910.)


bz2
---

The "BZ2Decompressor.decompress" method now accepts an optional
*max_length* argument to limit the maximum size of decompressed data.
(Contributed by Nikolaus Rath in issue 15955.)


cgi
---

The "FieldStorage" class now supports the context management protocol.
(Contributed by Berker Peksag in issue 20289.)


cmath
-----

A new function "isclose()" provides a way to test for approximate
equality. (Contributed by Chris Barker and Tal Einat in issue 24270.)


code
----

The "InteractiveInterpreter.showtraceback" method now prints the full
chained traceback, just like the interactive interpreter.
(Contributed by Claudiu Popa in issue 17442.)


collections
-----------

The "OrderedDict" class is now implemented in C, which makes it 4 to
100 times faster.  (Contributed by Eric Snow in issue 16991.)

"OrderedDict.items", "OrderedDict.keys", "OrderedDict.values" views
now support "reversed()" iteration. (Contributed by Serhiy Storchaka
in issue 19505.)

The "deque" class now defines "index()", "insert()", and "copy()", as
well as supports "+" and "*" operators. This allows deques to be
recognized as a "MutableSequence" and improves their substitutability
for lists. (Contributed by Raymond Hettinger issue 23704.)

Docstrings produced by "namedtuple()" can now be updated:

   Point = namedtuple('Point', ['x', 'y'])
   Point.__doc__ = 'ordered pair'
   Point.x.__doc__ = 'abscissa'
   Point.y.__doc__ = 'ordinate'

(Contributed by Berker Peksag in issue 24064.)

The "UserString" class now implements "__getnewargs__()",
"__rmod__()", "casefold()", "format_map()", "isprintable()", and
"maketrans()" methods to match corresponding methods of "str".
(Contributed by Joe Jevnik in issue 22189.)


collections.abc
---------------

A new "Generator" abstract base class. (Contributed by Stefan Behnel
in issue 24018.)

New "Coroutine", "AsyncIterator", and "AsyncIterable" abstract base
classes. (Contributed by Yury Selivanov in issue 24184.)


compileall
----------

A new "compileall" option, "-j N", allows to run "N" workers
sumultaneously to perform parallel bytecode compilation. The
"compile_dir()" function has a corresponding "workers" parameter.
(Contributed by Claudiu Popa in issue 16104.)

The "-q" command line option can now be specified more than once, in
which case all output, including errors, will be suppressed.  The
corresponding "quiet" parameter in "compile_dir()", "compile_file()",
and "compile_path()" can now accept an integer value indicating the
level of output suppression. (Contributed by Thomas Kluyver in issue
21338.)


concurrent.futures
------------------

The "Executor.map" method now accepts a *chunksize* argument to allow
batching of tasks to improve performance when "ProcessPoolExecutor()"
is used. (Contributed by Dan O'Reilly in issue 11271.)


contextlib
----------

The new "redirect_stderr()" context manager (similar to
"redirect_stdout()") makes it easier for utility scripts to handle
inflexible APIs that write their output to "sys.stderr" and don't
provide any options to redirect it.  (Contributed by Berker Peksag in
issue 22389.)


curses
------

The new "update_lines_cols()" function updates "LINES" and "COLS"
environment variables.  This is useful for detecting manual screen
resize.  (Contributed by Arnon Yaari in issue 4254.)


difflib
-------

The charset of HTML documents generated by "HtmlDiff.make_file" can
now be customized by using a new *charset* keyword-only argument. The
default charset of HTML document changed from ""ISO-8859-1"" to
""utf-8"". (Contributed by Berker Peksag in issue 2052.)

The "diff_bytes()" function can now compare lists of byte strings.
This fixes a regression from Python 2. (Contributed by Terry J. Reedy
and Greg Ward in issue 17445.)


distutils
---------

Both "build" and "build_ext" commands now accept a "-j" option to
enable parallel building of extension modules. (Contributed by Antoine
Pitrou in issue 5309.)

The "distutils" module now supports "xz" compression, and can be
enabled by passing "xztar" as an argument to "bdist --format".
(Contributed by Serhiy Storchaka in issue 16314.)


doctest
-------

The "DocTestSuite()" function returns an empty "unittest.TestSuite" if
*module* contains no docstrings instead of raising "ValueError".
(Contributed by Glenn Jones in issue 15916.)


email
-----

A new policy option "Policy.mangle_from_" controls whether or not
lines that start with ""From "" in email bodies are prefixed with a
"">"" character by generators.  The default is "True" for "compat32"
and "False" for all other policies. (Contributed by Milan Oberkirch in
issue 20098.)

A new "Message.get_content_disposition" method provides easy access to
a canonical value for the *Content-Disposition* header. (Contributed
by Abhilash Raj in issue 21083.)

A new policy option "EmailPolicy.utf8" can be set to "True" to encode
email headers using the UTF-8 charset instead of using encoded words.
This allows "Messages" to be formatted according to **RFC 6532** and
used with an SMTP server that supports the **RFC 6531** "SMTPUTF8"
extension.  (Contributed by R. David Murray in issue 24211.)


enum
----

The "Enum" callable has a new parameter *start* to specify the initial
number of enum values if only *names* are provided:

   >>> Animal = enum.Enum('Animal', 'cat dog', start=10)
   >>> Animal.cat
   <Animal.cat: 10>
   >>> Animal.dog
   <Animal.dog: 11>

(Contributed by Ethan Furman in issue 21706.)


faulthandler
------------

"enable()", "register()", "dump_traceback()" and
"dump_traceback_later()" functions now accept file descriptors in
addition to file-like objects. (Contributed by Wei Wu in issue 23566.)


functools
---------

Most of "lru_cache()" machinery is now implemented in C, making it
significantly faster.  (Contributed by Matt Joiner, Alexey Kachayev,
and Serhiy Storchaka in issue 14373.)


glob
----

"iglob()" and "glob()" functions now support recursive search in
subdirectories using the ""**"" pattern. (Contributed by Serhiy
Storchaka in issue 13968.)


heapq
-----

Element comparison in "merge()" can now be customized by passing a
*key function* in a new optional "key" keyword argument. A new
optional "reverse" keyword argument can be used to reverse element
comparison.  (Contributed by Raymond Hettinger in issue 13742.)


http
----

A new "HTTPStatus" enum that defines a set of HTTP status codes,
reason phrases and long descriptions written in English. (Contributed
by Demian Brecht in issue 21793.)


idlelib and IDLE
----------------

Since idlelib implements the IDLE shell and editor and is not intended
for import by other programs, it gets improvements with every release.
See "Lib/idlelib/NEWS.txt" for a cumulative list of changes since
3.4.0, as well as changes made in future 3.5.x releases. This file is
also available from the IDLE Help -> About Idle dialog.


imaplib
-------

The "IMAP4" class now supports context manager protocol. When used in
a "with" statement, the IMAP4 "LOGOUT" command will be called
automatically at the end of the block. (Contributed by Tarek Ziadé and
Serhiy Storchaka in issue 4972.)

The "imaplib" module now supports **RFC 5161** (ENABLE Extension) and
**RFC 6855** (UTF-8 Support) via the "IMAP4.enable" method.  A new
"IMAP4.utf8_enabled" attribute, tracks whether or not **RFC 6855**
support is enabled. (Contributed by Milan Oberkirch, R. David Murray,
and Maciej Szulik in issue 21800.)

The "imaplib" module now automatically encodes non-ASCII string
usernames and passwords using UTF-8, as recommended by the RFCs.
(Contributed by Milan Oberkirch in issue 21800.)


imghdr
------

The "what()" function now recognizes the OpenEXR format (contributed
by Martin Vignali and Claudiu Popa in issue 20295), and the WebP
format (contributed by Fabrice Aneche and Claudiu Popa in issue
20197.)


importlib
---------

The "util.LazyLoader" class allows for lazy loading of modules in
applications where startup time is important. (Contributed by Brett
Cannon in issue 17621.)

The "abc.InspectLoader.source_to_code" method is now a static method.
This makes it easier to initialize a module object with code compiled
from a string by running "exec(code, module.__dict__)". (Contributed
by Brett Cannon in issue 21156.)

The new "util.module_from_spec" function is now the preferred way to
create a new module.  As opposed to creating a "types.ModuleType"
instance directly, this new function will set the various import-
controlled attributes based on the passed-in spec object.
(Contributed by Brett Cannon in issue 20383.)


inspect
-------

Both "Signature" and "Parameter" classes are now picklable and
hashable.  (Contributed by Yury Selivanov in issue 20726 and issue
20334.)

A new "BoundArguments.apply_defaults" method provides a way to set
default values for missing arguments. (Contributed by Yury Selivanov
in issue 24190.)

A new class method "Signature.from_callable" makes subclassing of
"Signature" easier.  (Contributed by Yury Selivanov and Eric Snow in
issue 17373.)

The "signature()" function now accepts a "follow_wrapped" optional
keyword argument, which, when set to "False", disables automatic
following of "__wrapped__" links. (Contributed by Yury Selivanov in
issue 20691.)

A set of new functions to inspect *coroutine functions* and *coroutine
objects* has been added: "iscoroutine()", "iscoroutinefunction()",
"isawaitable()", "getcoroutinelocals()", and "getcoroutinestate()".
(Contributed by Yury Selivanov in issue 24017 and issue 24400.)

"stack()", "trace()", "getouterframes()", and "getinnerframes()"
functions now return a list of named tuples. (Contributed by Daniel
Shahaf in issue 16808.)


io
--

A new "BufferedIOBase.readinto1" method, that uses at most one call to
the underlying raw stream's "RawIOBase.read" (or "RawIOBase.readinto")
method. (Contributed by Nikolaus Rath in issue 20578.)


ipaddress
---------

Both "IPv4Network" and "IPv6Network" classes now accept an "(address,
netmask)" tuple argument, so as to easily construct network objects
from existing addresses.  (Contributed by Peter Moody and Antoine
Pitrou in issue 16531.)

A new "reverse_pointer>" attribute for "IPv4Network" and "IPv6Network"
classes returns the name of the reverse DNS PTR record. (Contributed
by Leon Weber in issue 20480.)


json
----

The "json.tool" command line interface now preserves the order of keys
in JSON objects passed in input.  The new "--sort-keys" option can be
used to sort the keys alphabetically. (Contributed by Berker Peksag in
issue 21650.)

JSON decoder now raises "json.JSONDecodeError" instead of
"ValueError".   (Contributed by Serhiy Storchaka in issue 19361.)


locale
------

A new "delocalize()" function can be used to convert a string into a
normalized number string, taking the "LC_NUMERIC" settings into
account. (Contributed by Cédric Krier in issue 13918.)


logging
-------

All logging methods ("Logger" "log()", "exception()", "critical()",
"debug()", etc.), now accept exception instances as an "exc_info"
argument, in addition to boolean values and exception tuples.
(Contributed by Yury Selivanov in issue 20537.)

The "handlers.HTTPHandler" class now accepts an optional
"ssl.SSLContext" instance to configure SSL settings used in an HTTP
connection. (Contributed by Alex Gaynor in issue 22788.)

The "handlers.QueueListener" class now takes a *respect_handler_level*
keyword argument which, if set to "True", will pass messages to
handlers taking handler levels into account. (Contributed by Vinay
Sajip.)


lzma
----

The "LZMADecompressor.decompress" method now accepts an optional
*max_length* argument to limit the maximum size of decompressed data.
(Contributed by Martin Panter in issue 15955.)


math
----

Two new constants have been added to the "math" module: "inf" and
"nan".  (Contributed by Mark Dickinson in issue 23185.)

A new function "isclose()" provides a way to test for approximate
equality. (Contributed by Chris Barker and Tal Einat in issue 24270.)

A new "gcd()" function has been added.  The "fractions.gcd()" function
is now deprecated. (Contributed by Mark Dickinson and Serhiy Storchaka
in issue 22486.)


operator
--------

"attrgetter()", "itemgetter()", and "methodcaller()" objects now
support pickling. (Contributed by Josh Rosenberg and Serhiy Storchaka
in issue 22955.)

New "matmul()" and "imatmul()" functions to perform matrix
multiplication. (Contributed by Benjamin Peterson in issue 21176.)


os
--

The new "scandir()" function returning an iterator of "DirEntry"
objects has been added.  If possible, "scandir()" extracts file
attributes while scanning a directory, removing the need to perform
subsequent system calls to determine file type or attributes, which
may significantly improve performance.  (Contributed by Ben Hoyt with
the help of Victor Stinner in issue 22524.)

On Windows, a new "stat_result.st_file_attributes" attribute is now
available.  It corresponds to "dwFileAttributes" member of the
"BY_HANDLE_FILE_INFORMATION" structure returned by
"GetFileInformationByHandle()".  (Contributed by Ben Hoyt in issue
21719.)

The "urandom()" function now uses "getrandom()" syscall on Linux 3.17
or newer, and "getentropy()" on OpenBSD 5.6 and newer, removing the
need to use "/dev/urandom" and avoiding failures due to potential file
descriptor exhaustion.  (Contributed by Victor Stinner in issue
22181.)

New "get_blocking()" and "set_blocking()" functions allow to get and
set a file descriptor blocking mode ("O_NONBLOCK".) (Contributed by
Victor Stinner in issue 22054.)

The "truncate()" and "ftruncate()" functions are now supported on
Windows.  (Contributed by Steve Dower in issue 23668.)

There is a new "os.path.commonpath()" function returning the longest
common sub-path of each passed pathname.  Unlike the
"os.path.commonprefix()" function, it always returns a valid path.
(Contributed by Rafik Draoui and Serhiy Storchaka in issue 10395.)


pathlib
-------

The new "Path.samefile" method can be used to check whether the path
points to the same file as other path, which can be either an another
"Path" object, or a string. (Contributed by Vajrasky Kok and Antoine
Pitrou in issue 19775.)

The "Path.mkdir" method how accepts a new optional "exist_ok" argument
to match "mkdir -p" and "os.makrdirs()" functionality.  (Contributed
by Berker Peksag in issue 21539.)

There is a new "Path.expanduser" method to expand "~" and "~user"
prefixes.  (Contributed by Serhiy Storchaka and Claudiu Popa in issue
19776.)

A new "Path.home" class method can be used to get an instance of
"Path" object representing the user’s home directory. (Contributed by
Victor Salgado and Mayank Tripathi in issue 19777.)

New "Path.write_text", "Path.read_text", "Path.write_bytes",
"Path.read_bytes" methods to simplify read/write operations on files.
(Contributed by Christopher Welborn in issue 20218.)


pickle
------

Nested objects, such as unbound methods or nested classes, can now be
pickled using *pickle protocols* older than protocol version 4.
Protocol version 4 already supports these cases.  (Contributed by
Serhiy Storchaka in issue 23611.)


poplib
------

A new "POP3.utf8" command enables **RFC 6856** (Internationalized
Email) support, if a POP server supports it. (Contributed by Milan
OberKirch in issue 21804.)


re
--

The number of capturing groups in regular expression is no longer
limited by 100.  (Contributed by Serhiy Storchaka in issue 22437.)

The "sub()" and "subn()" functions now replace unmatched groups with
empty strings instead of raising an exception. (Contributed by Serhiy
Storchaka in issue 1519638.)

The "re.error" exceptions have new attributes: "msg", "pattern",
"pos", "lineno", and "colno" that provide better context information
about the error. (Contributed by Serhiy Storchaka in issue 22578.)


readline
--------

A new "append_history_file()" function can be used to append the
specified number of trailing elements in history to the given file.
(Contributed by Bruno Cauet in issue 22940.)


selectors
---------

The new "DevpollSelector" supports efficient "/dev/poll" polling on
Solaris. (Contributed by Giampaolo Rodola' in issue 18931.)


shutil
------

The "move()" function now accepts a *copy_function* argument,
allowing, for example, the "copy()" function to be used instead of the
default "copy2()" if there is a need to ignore file metadata when
moving. (Contributed by Claudiu Popa in issue 19840.)

The "make_archive()" function now supports the *xztar* format.
(Contributed by Serhiy Storchaka in issue 5411.)


signal
------

On Windows, the "set_wakeup_fd()" function now also supports socket
handles.  (Contributed by Victor Stinner in issue 22018.)

Various "SIG*" constants in the "signal" module have been converted
into "Enums".  This allows meaningful names to be printed during
debugging, instead of integer "magic numbers". (Contributed by
Giampaolo Rodola' in issue 21076.)


smtpd
-----

Both "SMTPServer" and "SMTPChannel" classes now accept a *decode_data*
keyword argument to determine if the "DATA" portion of the SMTP
transaction is decoded using the ""utf-8"" codec or is instead
provided to the "SMTPServer.process_message" method as a byte string.
The default is "True" for backward compatibility reasons, but will
change to "False" in Python 3.6.  If *decode_data* is set to "False",
the "process_message()" method must be prepared to accept keyword
arguments. (Contributed by Maciej Szulik in issue 19662.)

The "SMTPServer" class now advertises the "8BITMIME" extension (**RFC
6152**) if *decode_data* has been set "True".  If the client specifies
"BODY=8BITMIME" on the "MAIL" command, it is passed to
"SMTPServer.process_message" via the "mail_options" keyword.
(Contributed by Milan Oberkirch and R.  David Murray in issue 21795.)

The "SMTPServer" class now also supports the "SMTPUTF8" extension
(**RFC 6531**: Internationalized Email).  If the client specified
"SMTPUTF8 BODY=8BITMIME" on the "MAIL" command, they are passed to
"SMTPServer.process_message" via the "mail_options" keyword.  It is
the responsibility of the "process_message()" method to correctly
handle the "SMTPUTF8" data.  (Contributed by Milan Oberkirch in issue
21725.)

It is now possible to provide, directly or via name resolution, IPv6
addresses in the "SMTPServer" constructor, and have it successfully
connect.  (Contributed by Milan Oberkirch in issue 14758.)


smtplib
-------

A new "SMTP.auth" method provides a convenient way to implement custom
authentication mechanisms. (Contributed by Milan Oberkirch in issue
15014.)

The "SMTP.set_debuglevel" method now accepts an additional debuglevel
(2), which enables timestamps in debug messages. (Contributed by Gavin
Chappell and Maciej Szulik in issue 16914.)

Both "SMTP.sendmail" and "SMTP.send_message" methods now support
support **RFC 6531** (SMTPUTF8). (Contributed by Milan Oberkirch and
R. David Murray in issue 22027.)


sndhdr
------

"what()" and "whathdr()" functions  now return a "namedtuple()".
(Contributed by Claudiu Popa in issue 18615.)


ssl
---


Memory BIO Support
~~~~~~~~~~~~~~~~~~

(Contributed by Geert Jansen in issue 21965.)

The new "SSLObject" class has been added to provide SSL protocol
support for cases when the network I/O capabilities of "SSLSocket" are
not necessary or suboptimal.  "SSLObject" represents an SSL protocol
instance, but does not implement any network I/O methods, and instead
provides a memory buffer interface.  The new "MemoryBIO" class can be
used to pass data between Python and an SSL protocol instance.

The memory BIO SSL support is primarily intended to be used in
frameworks implementing asynchronous I/O for which "SSLSocket"'s
readiness model ("select/poll") is inefficient.

A new "SSLContext.wrap_bio" method can be used to create a new
"SSLObject" instance.


Application-Layer Protocol Negotiation Support
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(Contributed by Benjamin Peterson in issue 20188.)

Where OpenSSL support is present, "ssl" module now implements
*Application-Layer Protocol Negotiation* TLS extension as described in
**RFC 7301**.

The new "SSLContext.set_alpn_protocols" can be used to specify which
protocols a socket should advertise during the TLS handshake.

The new "SSLSocket.selected_alpn_protocol" returns the protocol that
was selected during the TLS handshake. "HAS_ALPN" flag indicates
whether APLN support is present.


Other Changes
~~~~~~~~~~~~~

There is a new "SSLSocket.version" method to query the actual protocol
version in use. (Contributed by Antoine Pitrou in issue 20421.)

The "SSLSocket" class now implements a "SSLSocket.sendfile" method.
(Contributed by Giampaolo Rodola' in issue 17552.)

The "SSLSocket.send" method now raises either "ssl.SSLWantReadError"
or "ssl.SSLWantWriteError" exception on a non-blocking socket if the
operation would block. Previously, it would return "0".  (Contributed
by Nikolaus Rath in issue 20951.)

The "cert_time_to_seconds()" function now interprets the input time as
UTC and not as local time, per **RFC 5280**.  Additionally, the return
value is always an "int". (Contributed by Akira Li in issue 19940.)

New "SSLObject.shared_ciphers" and "SSLSocket.shared_ciphers" methods
return the list of ciphers sent by the client during the handshake.
(Contributed by Benjamin Peterson in issue 23186.)

The "SSLSocket.do_handshake", "SSLSocket.read", "SSLSocket.shutdown",
and "SSLSocket.write" methods of "ssl.SSLSocket" class no longer reset
the socket timeout every time bytes are received or sent. The socket
timeout is now the maximum total duration of the method. (Contributed
by Victor Stinner in issue 23853.)

The "match_hostname()" function now supports matching of IP addresses.
(Contributed by Antoine Pitrou in issue 23239.)


socket
------

Functions with timeouts now use a monotonic clock, instead of a system
clock. (Contributed by Victor Stinner in issue 22043.)

A new "socket.sendfile" method allows to send a file over a socket by
using the high-performance "os.sendfile()" function on UNIX resulting
in uploads being from 2 to 3 times faster than when using plain
"socket.send". (Contributed by Giampaolo Rodola' in issue 17552.)

The "socket.sendall" method no longer resets the socket timeout every
time bytes are received or sent.  The socket timeout is now the
maximum total duration to send all data. (Contributed by Victor
Stinner in issue 23853.)

The *backlog* argument of the "socket.listen" method is now optional.
By default it is set to "SOMAXCONN" or to "128" whichever is less.
(Contributed by Charles-François Natali in issue 21455.)


sqlite3
-------

The "Row" class now fully supports sequence protocol, in particular
"reversed()" iteration and slice indexing. (Contributed by Claudiu
Popa in issue 10203; by Lucas Sinclair, Jessica McKellar, and  Serhiy
Storchaka in issue 13583.)


subprocess
----------

The new "run()" function has been added. It runs the specified command
and and returns a "CompletedProcess" object, which describes a
finished process.  The new API is more consistent and is the
recommended approach to invoking subprocesses in Python code that does
not need to maintain compatibility with earlier Python versions.
(Contributed by Thomas Kluyver in issue 23342.)


sys
---

A new "set_coroutine_wrapper()" function allows setting a global hook
that will be called whenever a *coroutine object* is created by an
"async def" function.  A corresponding "get_coroutine_wrapper()" can
be used to obtain a currently set wrapper.  Both functions are
provisional, and are intended for debugging purposes only.
(Contributed by Yury Selivanov in issue 24017.)

A new "is_finalizing()" function can be used to check if the Python
interpreter is *shutting down*. (Contributed by Antoine Pitrou in
issue 22696.)


sysconfig
---------

The name of the user scripts directory on Windows now includes the
first two components of Python version. (Contributed by Paul Moore in
issue 23437.)


tarfile
-------

The *mode* argument of the "open()" function now accepts ""x"" to
request exclusive creation.  (Contributed by Berker Peksag in issue
21717.)

"TarFile.extractall" and "TarFile.extract" methods now take a keyword
argument *numeric_only*.  If set to "True", the extracted files and
directories will be owned by the numeric "uid" and "gid" from the
tarfile. If set to "False" (the default, and the behavior in versions
prior to 3.5), they will be owned by the named user and group in the
tarfile. (Contributed by Michael Vogt and Eric Smith in issue 23193.)


threading
---------

Both "Lock.acquire" and "RLock.acquire" methods now use a monotonic
clock for timeout management. (Contributed by Victor Stinner in issue
22043.)


time
----

The "monotonic()" function is now always available. (Contributed by
Victor Stinner in issue 22043.)


timeit
------

A new command line option "-u" or "--unit=U" can be used to specify
the time unit for the timer output.  Supported options are "usec",
"msec", or "sec".  (Contributed by Julian Gindi in issue 18983.)

The "timeit()" function has a new *globals* parameter for specifying
the namespace in which the code will be running. (Contributed by Ben
Roberts in issue 2527.)


tkinter
-------

The "tkinter._fix" module used for setting up the Tcl/Tk environment
on Windows has been replaced by a private function in the "_tkinter"
module which makes no permanent changes to environment variables.
(Contributed by Zachary Ware in issue 20035.)


traceback
---------

New "walk_stack()" and "walk_tb()" functions to conveniently traverse
frame and traceback objects. (Contributed by Robert Collins in issue
17911.)

New lightweight classes: "TracebackException", "StackSummary", and
"traceback.FrameSummary". (Contributed by Robert Collins in issue
17911.)

Both "print_tb()" and "print_stack()" functions now support negative
values for the *limit* argument. (Contributed by Dmitry Kazakov in
issue 22619.)


types
-----

A new "coroutine()" function to transform *generator* and "generator-
like" objects into *awaitables*. (Contributed by Yury Selivanov in
issue 24017.)

A new "CoroutineType" is the type of *coroutine* objects created by
"async def" functions. (Contributed by Yury Selivanov in issue 24400.)


urllib
------

A new "request.HTTPPasswordMgrWithPriorAuth" class allows HTTP Basic
Authentication credentials to be managed so as to eliminate
unnecessary "401" response handling, or to unconditionally send
credentials on the first request in order to communicate with servers
that return a "404" response instead of a "401" if the "Authorization"
header is not sent. (Contributed by Matej Cepl in issue 19494 and
Akshit Khurana in issue 7159.)

A new *quote_via* argument for the "parse.urlencode" function provides
a way to control the encoding of query parts if needed. (Contributed
by Samwyse and Arnon Yaari in issue 13866.)

The "request.urlopen" function accepts an "ssl.SSLContext" object as a
*context* argument, which will be used for the HTTPS connection.
(Contributed by Alex Gaynor in issue 22366.)

The "parse.urljoin" was updated to use the **RFC 3986** semantics for
the resolution of relative URLs, rather than **RFC 1808** and **RFC
2396**. (Contributed by Demian Brecht and Senthil Kumaran in issue
22118.)


unicodedata
-----------

The "unicodedata" module now uses data from Unicode 8.0.0.


unittest
--------

A new command line option "--locals" to show local variables in
tracebacks.  (Contributed by Robert Collins in issue 22936.)


unittest.mock
-------------

The "Mock" has the following improvements:

* Class constructor has a new *unsafe* parameter, which causes mock
  objects to raise "AttributeError" on attribute names starting with
  ""assert"". (Contributed by Kushal Das in issue 21238.)

* A new "Mock.assert_not_called" method to check if the mock object
  was called. (Contributed by Kushal Das in issue 21262.)

The "MagicMock" class now supports "__truediv__()", "__divmod__()" and
"__matmul__()" operators. (Contributed by Johannes Baiter in issue
20968, and Håkan Lövdahl in issue 23581 and issue 23568.)


wsgiref
-------

The *headers* argument of the "headers.Headers" class constructor is
now optional. (Contributed by Pablo Torres Navarrete and SilentGhost
in issue 5800.)


xmlrpc
------

The "client.ServerProxy" class is now a *context manager*.
(Contributed by Claudiu Popa in issue 20627.)

"client.ServerProxy" constructor now accepts an optional
"ssl.SSLContext" instance. (Contributed by Alex Gaynor in issue
22960.)


xml.sax
-------

SAX parsers now support a character stream of the
"xmlreader.InputSource" object. (Contributed by Serhiy Storchaka in
issue 2175.)


zipfile
-------

ZIP output can now be written to unseekable streams. (Contributed by
Serhiy Storchaka in issue 23252.)

The *mode* argument of "ZipFile.open" method now accepts ""x"" to
request exclusive creation. (Contributed by Serhiy Storchaka in issue
21717.)


Other module-level changes
==========================

Many functions in "mmap", "ossaudiodev", "socket", "ssl", and "codecs"
modules now accept writable *bytes-like objects*. (Contributed by
Serhiy Storchaka in issue 23001.)


Optimizations
=============

The "os.walk()" function has been sped up by 3 to 5 times on POSIX
systems, and by 7 to 20 times on Windows.  This was done using the new
"os.scandir()" function, which exposes file information from the
underlying "readdir" or "FindFirstFile"/"FindNextFile" system calls.
(Contributed by Ben Hoyt with help from Victor Stinner in issue
23605.)

Construction of "bytes(int)" (filled by zero bytes) is faster and uses
less memory for large objects. "calloc()" is used instead of
"malloc()" to allocate memory for these objects. (Contributed by
Victor Stinner in issue 21233.)

Some operations on "ipaddress" "IPv4Network" and "IPv6Network" have
been massively sped up, such as "subnets()", "supernet()",
"summarize_address_range()", "collapse_addresses()". The speed up can
range from 3 to 15 times. (Contributed by Antoine Pitrou, Michel
Albert, and Markus in issue 21486, issue 21487, issue 20826, issue
23266.)

Pickling of "ipaddress" objects was optimized to produce significantly
smaller output.  (Contributed by Serhiy Storchaka in issue 23133.)

Many operations on "io.BytesIO" are now 50% to 100% faster.
(Contributed by Serhiy Storchaka in issue 15381 and David Wilson in
issue 22003.)

The "marshal.dumps()" function is now faster: 65-85% with versions 3
and 4, 20-25% with versions 0 to 2 on typical data, and up to 5 times
in best cases. (Contributed by Serhiy Storchaka in issue 20416 and
issue 23344.)

The UTF-32 encoder is now 3 to 7 times faster. (Contributed by Serhiy
Storchaka in issue 15027.)

Regular expressions are now parsed up to 10% faster. (Contributed by
Serhiy Storchaka in issue 19380.)

The "json.dumps()" function was optimized to run with
"ensure_ascii=False" as fast as with "ensure_ascii=True". (Contributed
by Naoki Inada in issue 23206.)

The "PyObject_IsInstance()" and "PyObject_IsSubclass()" functions have
been sped up in the common case that the second argument has "type" as
its metaclass. (Contributed Georg Brandl by in issue 22540.)

Method caching was slightly improved, yielding up to 5% performance
improvement in some benchmarks. (Contributed by Antoine Pitrou in
issue 22847.)

Objects from "random" module now use two times less memory on 64-bit
builds.  (Contributed by Serhiy Storchaka in issue 23488.)

The "property()" getter calls are up to 25% faster. (Contributed by
Joe Jevnik in issue 23910.)

Instantiation of "fractions.Fraction" is now up to 30% faster.
(Contributed by Stefan Behnel in issue 22464.)

String methods "find()", "rfind()", "split()", "partition()" and "in"
string operator are now significantly faster for searching 1-character
substrings. (Contributed by Serhiy Storchaka in issue 23573.)


Build and C API Changes
=======================

New "calloc" functions were added:

   * "PyMem_RawCalloc()",

   * "PyMem_Calloc()",

   * "PyObject_Calloc()",

   * "_PyObject_GC_Calloc()".

(Contributed by Victor Stinner in issue 21233.)

New encoding/decoding helper functions:

   * "Py_DecodeLocale()" (replaced "_Py_char2wchar()"),

   * "Py_EncodeLocale()" (replaced "_Py_wchar2char()").

(Contributed by Victor Stinner in issue 18395.)

A new "PyCodec_NameReplaceErrors()" function to replace the unicode
encode error with "\N{...}" escapes. (Contributed by Serhiy Storchaka
in issue 19676.)

A new "PyErr_FormatV()" function similar to "PyErr_Format()", but
accepts a "va_list" argument. (Contributed by Antoine Pitrou in issue
18711.)

A new "PyExc_RecursionError" exception. (Contributed by Georg Brandl
in issue 19235.)

New "PyModule_FromDefAndSpec()", "PyModule_FromDefAndSpec2()", and
"PyModule_ExecDef()" introduced by **PEP 489** -- multi-phase
extension module initialization. (Contributed by Petr Viktorin in
issue 24268.)

New "PyNumber_MatrixMultiply()" and "PyNumber_InPlaceMatrixMultiply()"
functions to perform matrix multiplication. (Contributed by Benjamin
Peterson in issue 21176.  See also **PEP 465** for details.)

The "PyTypeObject.tp_finalize" slot is now part of stable ABI.

Windows builds now require Microsoft Visual C++ 14.0, which is
available as part of Visual Studio 2015.

Extension modules now include platform information tag in their
filename on some platforms (the tag is optional, and CPython will
import extensions without it; although if the tag is present and
mismatched, the extension won't be loaded):

* On Linux, extension module filenames end with
  ".cpython-<major><minor>m-<architecture>-<os>.pyd":

  * "<major>" is the major number of the Python version; for Python
    3.5 this is "3".

  * "<minor>" is the minor number of the Python version; for Python
    3.5 this is "5".

  * "<architecture>" is the hardware architecture the extension
    module was built to run on. It's most commonly either "i386" for
    32-bit Intel platforms or "x86_64" for 64-bit Intel (and AMD)
    platforms.

  * "<os>" is always "linux-gnu", except for extensions built to
    talk to the 32-bit ABI on 64-bit platforms, in which case it is
    "linux- gnu32" (and "<architecture>" will be "x86_64").

* On Windows, extension module filenames end with
  "<debug>.cp<major><minor>-<platform>.pyd":

  * "<major>" is the major number of the Python version; for Python
    3.5 this is "3".

  * "<minor>" is the minor number of the Python version; for Python
    3.5 this is "5".

  * "<platform>" is the platform the extension module was built for,
    either "win32" for Win32, "win_amd64" for Win64, "win_ia64" for
    Windows Itanium 64, and "win_arm" for Windows on ARM.

  * If built in debug mode, "<debug>" will be "_d", otherwise it
    will be blank.

* On OS X platforms, extension module filenames now end with
  "-darwin.so".

* On all other platforms, extension module filenames are the same as
  they were with Python 3.4.


Deprecated
==========


New Keywords
------------

"async" and "await" are not recommended to be used as variable, class,
function or module names.  Introduced by **PEP 492** in Python 3.5,
they will become proper keywords in Python 3.7.


Unsupported Operating Systems
-----------------------------

Windows XP is no longer supported by Microsoft, thus, per **PEP 11**,
CPython 3.5 is no longer officially supported on this OS.


Deprecated Python modules, functions and methods
------------------------------------------------

The "formatter" module has now graduated to full deprecation and is
still slated for removal in Python 3.6.

The "asyncio.async()" function is deprecated in favor of
"ensure_future()".

The "smtpd" module has in the past always decoded the DATA portion of
email messages using the "utf-8" codec.  This can now be controlled by
the new *decode_data* keyword to "SMTPServer".  The default value is
"True", but this default is deprecated.  Specify the *decode_data*
keyword with an appropriate value to avoid the deprecation warning.

Directly assigning values to the "key", "value" and "coded_value" of
"Morsel" objects is deprecated.  Use the "set()" method instead.  In
addition, the undocumented *LegalChars* parameter of "set()" is
deprecated, and is now ignored.

Passing a format string as keyword argument *format_string* to the
"format()" method of the "string.Formatter" class has been deprecated.

The "platform.dist()" and "platform.linux_distribution()" functions
are now deprecated and will be removed in Python 3.7.  Linux
distributions use too many different ways of describing themselves, so
the functionality is left to a package. (Contributed by Vajrasky Kok
and Berker Peksag in issue 1322.)

The previously undocumented "from_function" and "from_builtin" methods
of "inspect.Signature" are deprecated.  Use new
"inspect.Signature.from_callable()" instead. (Contributed by Yury
Selivanov in issue 24248.)

The "inspect.getargspec()" function is deprecated and scheduled to be
removed in Python 3.6.  (See issue 20438 for details.)

The "inspect" "getfullargspec()", "getargvalues()", "getcallargs()",
"getargvalues()", "formatargspec()", and "formatargvalues()" functions
are deprecated in favor of "inspect.signature()" API. (Contributed by
Yury Selivanov in issue 20438.)

Use of "re.LOCALE" flag with str patterns or "re.ASCII" is now
deprecated.  (Contributed by Serhiy Storchaka in issue 22407.)


Removed
=======


API and Feature Removals
------------------------

The following obsolete and previously deprecated APIs and features
have been removed:

* The "__version__" attribute has been dropped from the email
  package. The email code hasn't been shipped separately from the
  stdlib for a long time, and the "__version__" string was not updated
  in the last few releases.

* The internal "Netrc" class in the "ftplib" module was deprecated
  in 3.4, and has now been removed. (Contributed by Matt Chaput in
  issue 6623.)

* The concept of ".pyo" files has been removed.

* The JoinableQueue class in the provisional asyncio module was
  deprecated in 3.4.4 and is now removed. (Contributed by A. Jesse
  Jiryu Davis in issue 23464.)


Porting to Python 3.5
=====================

This section lists previously described changes and other bugfixes
that may require changes to your code.


Changes in the Python API
-------------------------

* **PEP 475**: System calls are now retried when interrupted by a
  signal instead of raising "InterruptedError" if the Python signal
  handler does not raise an exception.

* Before Python 3.5, a "datetime.time" object was considered to be
  false if it represented midnight in UTC.  This behavior was
  considered obscure and error-prone and has been removed in Python
  3.5.  See issue 13936 for full details.

* The "ssl.SSLSocket.send()" method now raises either
  "ssl.SSLWantReadError" or "ssl.SSLWantWriteError" on a non-blocking
  socket if the operation would block.  Previously, it would return
  "0".  (Contributed by Nikolaus Rath in issue 20951.)

* The "__name__" attribute of generator is now set from the function
  name, instead of being set from the code name. Use
  "gen.gi_code.co_name" to retrieve the code name. Generators also
  have a new "__qualname__" attribute, the qualified name, which is
  now used for the representation of a generator ("repr(gen)").
  (Contributed by Victor Stinner in issue 21205.)

* The deprecated "strict" mode and argument of "HTMLParser",
  "HTMLParser.error()", and the "HTMLParserError" exception have been
  removed.  (Contributed by Ezio Melotti in issue 15114.) The
  *convert_charrefs* argument of "HTMLParser" is now "True" by
  default.  (Contributed by Berker Peksag in issue 21047.)

* Although it is not formally part of the API, it is worth noting
  for porting purposes (ie: fixing tests) that error messages that
  were previously of the form "'sometype' does not support the buffer
  protocol" are now of the form "a *bytes-like object* is required,
  not 'sometype'". (Contributed by Ezio Melotti in issue 16518.)

* If the current directory is set to a directory that no longer
  exists then "FileNotFoundError" will no longer be raised and instead
  "find_spec()" will return "None" **without** caching "None" in
  "sys.path_importer_cache" which is different than the typical case
  (issue 22834).

* HTTP status code and messages from "http.client" and "http.server"
  were refactored into a common "HTTPStatus" enum.  The values in
  "http.client" and "http.server" remain available for backwards
  compatibility.  (Contributed by Demian Brecht in issue 21793.)

* When an import loader defines "exec_module()" it is now expected
  to also define "create_module()" (raises a "DeprecationWarning" now,
  will be an error in Python 3.6). If the loader inherits from
  "importlib.abc.Loader" then there is nothing to do, else simply
  define "create_module()" to return "None".  (Contributed by Brett
  Cannon in issue 23014.)

* The "re.split()" function always ignored empty pattern matches, so
  the ""x*"" pattern worked the same as ""x+"", and the ""\b"" pattern
  never worked.  Now "re.split()" raises a warning if the pattern
  could match an empty string.  For compatibility use patterns that
  never match an empty string (e.g. ""x+"" instead of ""x*"").
  Patterns that could only match an empty string (such as ""\b"") now
  raise an error.

* The "Morsel" dict-like interface has been made self consistent:
  morsel comparison now takes the "key" and "value" into account,
  "copy()" now results in a "Morsel" instance rather than a "dict",
  and "update()" will now raise an exception if any of the keys in the
  update dictionary are invalid.  In addition, the undocumented
  *LegalChars* parameter of "set()" is deprecated and is now ignored.
  (Contributed by Demian Brecht in issue 2211.)

* **PEP 488** has removed ".pyo" files from Python and introduced
  the optional "opt-" tag in ".pyc" file names. The
  "importlib.util.cache_from_source()" has gained an *optimization*
  parameter to help control the "opt-" tag. Because of this, the
  *debug_override* parameter of the function is now deprecated. *.pyo*
  files are also no longer supported as a file argument to the Python
  interpreter and thus serve no purpose when distributed on their own
  (i.e. sourcless code distribution). Due to the fact that the magic
  number for bytecode has changed in Python 3.5, all old *.pyo* files
  from previous versions of Python are invalid regardless of this PEP.

* The "socket" module now exports the "CAN_RAW_FD_FRAMES" constant
  on linux 3.6 and greater.

* The "cert_time_to_seconds()" function now interprets the input
  time as UTC and not as local time, per **RFC 5280**.  Additionally,
  the return value is always an "int". (Contributed by Akira Li in
  issue 19940.)

* The "pygettext.py" Tool now uses the standard +NNNN format for
  timezones in the POT-Creation-Date header.

* The "smtplib" module now uses "sys.stderr" instead of previous
  module level "stderr" variable for debug output.  If your (test)
  program depends on patching the module level variable to capture the
  debug output, you will need to update it to capture sys.stderr
  instead.

* The "str.startswith()" and "str.endswith()" methods no longer
  return "True" when finding the empty string and the indexes are
  completely out of range.  (Contributed by Serhiy Storchaka in issue
  24284.)

* The "inspect.getdoc()" function now returns documentation strings
  inherited from base classes.  Documentation strings no longer need
  to be duplicated if the inherited documentation is appropriate.  To
  suppress an inherited string, an empty string must be specified (or
  the documentation may be filled in).  This change affects the output
  of the "pydoc" module and the "help()" function. (Contributed by
  Serhiy Storchaka in issue 15582.)


Changes in the C API
--------------------

* The undocumented "format" member of the (non-public)
  "PyMemoryViewObject" structure has been removed. All extensions
  relying on the relevant parts in "memoryobject.h" must be rebuilt.

* The "PyMemAllocator" structure was renamed to "PyMemAllocatorEx"
  and a new "calloc" field was added.

* Removed non-documented macro "PyObject_REPR" which leaked
  references. Use format character "%R" in
  "PyUnicode_FromFormat()"-like functions to format the "repr()" of
  the object. (Contributed by Serhiy Storchaka in issue 22453.)

* Because the lack of the "__module__" attribute breaks pickling and
  introspection, a deprecation warning now is raised for builtin type
  without the "__module__" attribute.  Would be an AttributeError in
  future. (Contributed by Serhiy Storchaka in issue 20204.)

* As part of **PEP 492** implementation, "tp_reserved" slot of
  "PyTypeObject" was replaced with a "tp_as_async" slot.  Refer to
  *Coroutine Objects* for new types, structures and functions.
