What’s New In Python 3.5
************************

Editors:
   Elvis Pranskevichus <elvis@magic.io>, Yury Selivanov
   <yury@magic.io>

This article explains the new features in Python 3.5, compared to 3.4.
Python 3.5 was released on September 13, 2015.  See the changelog for
a full list of changes.

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:

* "typing": PEP 484 – Type Hints.

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

New built-in features:

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

* New "bytes.hex()", "bytearray.hex()" and "memoryview.hex()" methods.
  (Contributed by Arnon Yaari in bpo-9951.)

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

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

* A new "RecursionError" exception is now raised when maximum
  recursion depth is reached.  (Contributed by Georg Brandl in
  bpo-19235.)

CPython implementation improvements:

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

* ".pyo" files are no longer used and have been replaced by a more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

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

Significant improvements in the standard library:

* "collections.OrderedDict" is now implemented in C, which makes it 4
  to 100 times faster.

* The "ssl" module gained support for Memory BIO, which decouples SSL
  protocol handling from network IO.

* The new "os.scandir()" function provides a better and significantly
  faster way of directory traversal.

* "functools.lru_cache()" has been mostly reimplemented in C, yielding
  much better performance.

* The new "subprocess.run()" function provides a streamlined way to
  run subprocesses.

* The "traceback" module has been significantly enhanced for improved
  performance and developer convenience.

Security improvements:

* SSLv3 is now disabled throughout the standard library. It can still
  be enabled by instantiating a "ssl.SSLContext" manually.  (See
  bpo-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
  bpo-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 rudimentary 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 output:

   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 the asyncio loop.

Note:

  Changed in version 3.5.2: Starting with CPython 3.5.2, "__aiter__"
  can directly return *asynchronous iterators*.  Returning an
  *awaitable* object will result in a "PendingDeprecationWarning".See
  more details in the Asynchronous Iterators documentation section.

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))

NumPy 1.10 has 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 (see Expression lists and Dictionary displays):

   >>> *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 - percent formatting support for bytes and bytearray
------------------------------------------------------------

**PEP 461** adds support for the "%" interpolation operator to "bytes"
and "bytearray".

While interpolation is usually thought of as a string operation, there
are cases where interpolation on "bytes" or "bytearrays" makes sense,
and the work needed to make up for this missing functionality detracts
from the overall readability of the code.  This issue is particularly
important when dealing with wire format protocols, which are often a
mixture of binary and ASCII compatible text.

Examples:

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

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

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

   >>> b'Hello %b!' % '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'"

Note that "%s" and "%r" conversion types, although supported, should
only be used in codebases that need compatibility with Python 2.

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
--------------------

Function annotation syntax has been a Python feature since version 3.0
(**PEP 3107**), however the semantics of annotations has been left
undefined.

Experience has shown that the majority of function annotation uses
were to provide type hints to function parameters and return values.
It became evident that it would be beneficial for Python users, if the
standard library included the base definitions and tools for type
annotations.

**PEP 484** 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

While these annotations are available at runtime through the usual
"__annotations__" attribute, *no automatic type checking happens at
runtime*.  Instead, it is assumed that a separate off-line type
checker (e.g. mypy) will be used for on-demand source code analysis.

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 483** – The Theory of Type Hints
       PEP written 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 "scandir", which makes it 3 to 5 times faster on POSIX systems
and 7 to 20 times faster on Windows systems.  This is largely achieved
by greatly reducing the number of calls to "os.stat()" required to
walk a directory tree.

Additionally, "scandir" returns an iterator, as opposed to returning a
list of file names, which improves memory efficiency when iterating
over very large directories.

The following example shows a simple use of "os.scandir()" to display
all the files (excluding directories) in the given *path* that don’t
start with "'.'". The "entry.is_file()" call will generally not make
an additional system call:

   for entry in os.scandir(path):
       if not entry.name.startswith('.') and entry.is_file():
           print(entry.name)

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
----------------------------------------------

An "errno.EINTR" error code is returned whenever a system call, that
is waiting for I/O, is interrupted by a signal.  Previously, Python
would raise "InterruptedError" in such cases.  This meant that, when
writing a Python application, the developer had two choices:

1. Ignore the "InterruptedError".

2. Handle the "InterruptedError" and attempt to restart the
   interrupted system call at every call site.

The first option makes an application fail intermittently. The second
option adds a large amount of boilerplate that makes the code nearly
unreadable.  Compare:

   print("Hello World")

and:

   while True:
       try:
           print("Hello World")
           break
       except InterruptedError:
           continue

**PEP 475** implements automatic retry of system calls on "EINTR".
This removes the burden of dealing with "EINTR" or "InterruptedError"
in user code in most situations and makes Python programs, including
the standard library, more robust.  Note that the system call is only
retried if the signal handler does not raise an exception.

Below is a list of functions which are now retried when interrupted by
a signal:

* "open()" and "io.open()";

* functions of the "faulthandler" module;

* "os" functions: "fchdir()", "fchmod()", "fchown()", "fdatasync()",
  "fstat()", "fstatvfs()", "fsync()", "ftruncate()", "mkfifo()",
  "mknod()", "open()", "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"
  errors; the syscall is not retried (see the PEP for the rationale);

* "select" functions: "devpoll.poll()", "epoll.poll()",
  "kqueue.control()", "poll.poll()", "select()";

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

* "signal.sigtimedwait()" and "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
--------------------------------------------------------

The interaction of generators and "StopIteration" in Python 3.4 and
earlier was sometimes surprising, and could conceal obscure bugs.
Previously, "StopIteration" raised accidentally inside a generator
function was interpreted as the end of the iteration by the loop
construct driving the generator.

**PEP 479** changes the behavior of generators: when a "StopIteration"
exception is raised inside a generator, it is replaced with a
"RuntimeError" before it exits the generator frame.  The main goal of
this change is to ease debugging in the situation where an unguarded
"next()" call raises "StopIteration" and causes the iteration
controlled by the generator to terminate silently. This is
particularly pernicious in combination with the "yield from"
construct.

This is a backwards incompatible change, so to enable the new
behavior, a *__future__* import is necessary:

   >>> from __future__ import generator_stop

   >>> def gen():
   ...     next(iter([]))
   ...     yield
   ...
   >>> next(gen())
   Traceback (most recent call last):
     File "<stdin>", line 2, in gen
   StopIteration

   The above exception was the direct cause of the following exception:

   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   RuntimeError: generator raised StopIteration

Without a "__future__" import, a "PendingDeprecationWarning" will be
raised whenever a "StopIteration" exception is raised inside a
generator.

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 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.
Relative tolerance is the maximum allowed difference between "isclose"
arguments, relative to the larger absolute value:

   >>> import math
   >>> a = 5.0
   >>> b = 4.99998
   >>> math.isclose(a, b, rel_tol=1e-5)
   True
   >>> math.isclose(a, b, rel_tol=1e-6)
   False

It is also possible to compare two values using absolute tolerance,
which must be a non-negative value:

   >>> import math
   >>> a = 5.0
   >>> b = 4.99998
   >>> math.isclose(a, b, abs_tol=0.00003)
   True
   >>> math.isclose(a, b, abs_tol=0.00001)
   False

See also:

  **PEP 485** – A function for testing approximate equality
     PEP written by Christopher Barker; implemented by Chris Barker
     and Tal Einat.


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.


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

Some smaller changes made to the core Python language are:

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

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

* New Kazakh "kz1048" and Tajik "koi8_t" codecs. (Contributed by
  Serhiy Storchaka in bpo-22682 and bpo-22681.)

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

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


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


typing
------

The new "typing" *provisional* module provides standard definitions
and tools for function type annotations. See Type Hints for more
information.


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 bpo-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
bpo-23491.

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


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


argparse
--------

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


asyncio
-------

Since the "asyncio" module is *provisional*, all changes introduced in
Python 3.5 have also been backported to Python 3.4.x.

Notable changes in the "asyncio" module since Python 3.4.0:

* New debugging APIs: "loop.set_debug()" and "loop.get_debug()"
  methods. (Contributed by Victor Stinner.)

* The proactor event loop now supports SSL. (Contributed by Antoine
  Pitrou and Victor Stinner in bpo-22560.)

* A new "loop.is_closed()" method to check if the event loop is
  closed. (Contributed by Victor Stinner in bpo-21326.)

* A new "loop.create_task()" to conveniently create and schedule a new
  "Task" for a coroutine.  The "create_task" method is also used by
  all asyncio functions that wrap coroutines into tasks, such as
  "asyncio.wait()", "asyncio.gather()", etc. (Contributed by Victor
  Stinner.)

* A new "transport.get_write_buffer_limits()" method to inquire for
  *high-* and *low-* water limits of the flow control. (Contributed by
  Victor Stinner.)

* The "async()" function is deprecated in favor of "ensure_future()".
  (Contributed by Yury Selivanov.)

* New "loop.set_task_factory()" and "loop.get_task_factory()" methods
  to customize the task factory that "loop.create_task()" method uses.
  (Contributed by Yury Selivanov.)

* New "Queue.join()" and "Queue.task_done()" queue methods.
  (Contributed by Victor Stinner.)

* The "JoinableQueue" class was removed, in favor of the
  "asyncio.Queue" class. (Contributed by Victor Stinner.)

Updates in 3.5.1:

* The "ensure_future()" function and all functions that use it, such
  as "loop.run_until_complete()", now accept all kinds of *awaitable
  objects*. (Contributed by Yury Selivanov.)

* New "run_coroutine_threadsafe()" function to submit coroutines to
  event loops from other threads. (Contributed by Vincent Michel.)

* New "Transport.is_closing()" method to check if the transport is
  closing or closed. (Contributed by Yury Selivanov.)

* The "loop.create_server()" method can now accept a list of hosts.
  (Contributed by Yann Sionneau.)

Updates in 3.5.2:

* New "loop.create_future()" method to create Future objects.  This
  allows alternative event loop implementations, such as uvloop, to
  provide a faster "asyncio.Future" implementation. (Contributed by
  Yury Selivanov.)

* New "loop.get_exception_handler()" method to get the current
  exception handler. (Contributed by Yury Selivanov.)

* New "StreamReader.readuntil()" method to read data from the stream
  until a separator bytes sequence appears. (Contributed by Mark
  Korenberg.)

* The "loop.create_connection()" and "loop.create_server()" methods
  are optimized to avoid calling the system "getaddrinfo" function if
  the address is already resolved. (Contributed by A. Jesse Jiryu
  Davis.)

* The "loop.sock_connect(sock, address)" no longer requires the
  *address* to be resolved prior to the call. (Contributed by A. Jesse
  Jiryu Davis.)


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 bpo-15955.)


cgi
---

The "FieldStorage" class now supports the *context manager* protocol.
(Contributed by Berker Peksag in bpo-20289.)


cmath
-----

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


code
----

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


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

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

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

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

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

   Point = namedtuple('Point', ['x', 'y'])
   Point.__doc__ += ': Cartesian coordinate'
   Point.x.__doc__ = 'abscissa'
   Point.y.__doc__ = 'ordinate'

(Contributed by Berker Peksag in bpo-24064.)

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


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

The "Sequence.index()" method now accepts *start* and *stop* arguments
to match the corresponding methods of "tuple", "list", etc.
(Contributed by Devin Jeanpierre in bpo-23086.)

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

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

For earlier Python versions, a backport of the new ABCs is available
in an external PyPI package.


compileall
----------

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

Another new option, "-r", allows controlling the maximum recursion
level for subdirectories.  (Contributed by Claudiu Popa in bpo-19628.)

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
bpo-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
bpo-11271.)

The number of workers in the "ThreadPoolExecutor" constructor is
optional now.  The default value is 5 times the number of CPUs.
(Contributed by Claudiu Popa in bpo-21527.)


configparser
------------

"configparser" now provides a way to customize the conversion of
values by specifying a dictionary of converters in the "ConfigParser"
constructor, or by defining them as methods in "ConfigParser"
subclasses.  Converters defined in a parser instance are inherited by
its section proxies.

Example:

   >>> import configparser
   >>> conv = {}
   >>> conv['list'] = lambda v: [e.strip() for e in v.split() if e.strip()]
   >>> cfg = configparser.ConfigParser(converters=conv)
   >>> cfg.read_string("""
   ... [s]
   ... list = a b c d e f g
   ... """)
   >>> cfg.get('s', 'list')
   'a b c d e f g'
   >>> cfg.getlist('s', 'list')
   ['a', 'b', 'c', 'd', 'e', 'f', 'g']
   >>> section = cfg['s']
   >>> section.getlist('list')
   ['a', 'b', 'c', 'd', 'e', 'f', 'g']

(Contributed by Łukasz Langa in bpo-18159.)


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:

   >>> import contextlib, io, logging
   >>> f = io.StringIO()
   >>> with contextlib.redirect_stderr(f):
   ...     logging.warning('warning')
   ...
   >>> f.getvalue()
   'WARNING:root:warning\n'

(Contributed by Berker Peksag in bpo-22389.)


csv
---

The "writerow()" method now supports arbitrary iterables, not just
sequences.  (Contributed by Serhiy Storchaka in bpo-23171.)


curses
------

The new "update_lines_cols()" function updates the "LINES" and "COLS"
module variables.  This is useful for detecting manual screen
resizing.  (Contributed by Arnon Yaari in bpo-4254.)


dbm
---

"dumb.open" always creates a new database when the flag has the value
""n"".  (Contributed by Claudiu Popa in bpo-18039.)


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 bpo-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 bpo-17445.)


distutils
---------

Both the "build" and "build_ext" commands now accept a "-j" option to
enable parallel building of extension modules. (Contributed by Antoine
Pitrou in bpo-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 bpo-16314.)


doctest
-------

The "DocTestSuite()" function returns an empty "unittest.TestSuite" if
*module* contains no docstrings, instead of raising "ValueError".
(Contributed by Glenn Jones in bpo-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
bpo-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 bpo-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 bpo-24211.)

The "mime.text.MIMEText" constructor now accepts a "charset.Charset"
instance. (Contributed by Claude Paroz and Berker Peksag in
bpo-16324.)


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 bpo-21706.)


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

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


functools
---------

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


glob
----

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


gzip
----

The *mode* argument of the "GzipFile" constructor now accepts ""x"" to
request exclusive creation. (Contributed by Tim Heaney in bpo-19222.)


heapq
-----

Element comparison in "merge()" can now be customized by passing a
*key function* in a new optional *key* keyword argument, and a new
optional *reverse* keyword argument can be used to reverse element
comparison:

   >>> import heapq
   >>> a = ['9', '777', '55555']
   >>> b = ['88', '6666']
   >>> list(heapq.merge(a, b, key=len))
   ['9', '88', '777', '6666', '55555']
   >>> list(heapq.merge(reversed(a), reversed(b), key=len, reverse=True))
   ['55555', '6666', '777', '88', '9']

(Contributed by Raymond Hettinger in bpo-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 bpo-21793.)


http.client
-----------

"HTTPConnection.getresponse()" now raises a "RemoteDisconnected"
exception when a remote server connection is closed unexpectedly.
Additionally, if a "ConnectionError" (of which "RemoteDisconnected" is
a subclass) is raised, the client socket is now closed automatically,
and will reconnect on the next request:

   import http.client
   conn = http.client.HTTPConnection('www.python.org')
   for retries in range(3):
       try:
           conn.request('GET', '/')
           resp = conn.getresponse()
       except http.client.RemoteDisconnected:
           pass

(Contributed by Martin Panter in bpo-3566.)


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 the *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 bpo-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 bpo-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 bpo-21800.)


imghdr
------

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


importlib
---------

The "util.LazyLoader" class allows for lazy loading of modules in
applications where startup time is important. (Contributed by Brett
Cannon in bpo-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 bpo-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 bpo-20383.)


inspect
-------

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

A new "BoundArguments.apply_defaults()" method provides a way to set
default values for missing arguments:

   >>> def foo(a, b='ham', *args): pass
   >>> ba = inspect.signature(foo).bind('spam')
   >>> ba.apply_defaults()
   >>> ba.arguments
   OrderedDict([('a', 'spam'), ('b', 'ham'), ('args', ())])

(Contributed by Yury Selivanov in bpo-24190.)

A new class method "Signature.from_callable()" makes subclassing of
"Signature" easier.  (Contributed by Yury Selivanov and Eric Snow in
bpo-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
bpo-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 bpo-24017 and bpo-24400.)

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


io
--

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


ipaddress
---------

Both the "IPv4Network" and "IPv6Network" classes now accept an
"(address, netmask)" tuple argument, so as to easily construct network
objects from existing addresses:

   >>> import ipaddress
   >>> ipaddress.IPv4Network(('127.0.0.0', 8))
   IPv4Network('127.0.0.0/8')
   >>> ipaddress.IPv4Network(('127.0.0.0', '255.0.0.0'))
   IPv4Network('127.0.0.0/8')

(Contributed by Peter Moody and Antoine Pitrou in bpo-16531.)

A new "reverse_pointer" attribute for the "IPv4Network" and
"IPv6Network" classes returns the name of the reverse DNS PTR record:

   >>> import ipaddress
   >>> addr = ipaddress.IPv4Address('127.0.0.1')
   >>> addr.reverse_pointer
   '1.0.0.127.in-addr.arpa'
   >>> addr6 = ipaddress.IPv6Address('::1')
   >>> addr6.reverse_pointer
   '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa'

(Contributed by Leon Weber in bpo-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
bpo-21650.)

JSON decoder now raises "JSONDecodeError" instead of "ValueError" to
provide better context information about the error. (Contributed by
Serhiy Storchaka in bpo-19361.)


linecache
---------

A new "lazycache()" function can be used to capture information about
a non-file-based module to permit getting its lines later via
"getline()". This avoids doing I/O until a line is actually needed,
without having to carry the module globals around indefinitely.
(Contributed by Robert Collins in bpo-17911.)


locale
------

A new "delocalize()" function can be used to convert a string into a
normalized number string, taking the "LC_NUMERIC" settings into
account:

   >>> import locale
   >>> locale.setlocale(locale.LC_NUMERIC, 'de_DE.UTF-8')
   'de_DE.UTF-8'
   >>> locale.delocalize('1.234,56')
   '1234.56'
   >>> locale.setlocale(locale.LC_NUMERIC, 'en_US.UTF-8')
   'en_US.UTF-8'
   >>> locale.delocalize('1,234.56')
   '1234.56'

(Contributed by Cédric Krier in bpo-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:

   >>> import logging
   >>> try:
   ...     1/0
   ... except ZeroDivisionError as ex:
   ...     logging.error('exception', exc_info=ex)
   ERROR:root:exception

(Contributed by Yury Selivanov in bpo-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 bpo-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 bpo-15955.)


math
----

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

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

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


multiprocessing
---------------

"sharedctypes.synchronized()" objects now support the *context
manager* protocol. (Contributed by Charles-François Natali in
bpo-21565.)


operator
--------

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

New "matmul()" and "imatmul()" functions to perform matrix
multiplication. (Contributed by Benjamin Peterson in bpo-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 bpo-22524.)

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

The "urandom()" function now uses the "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
bpo-22181.)

New "get_blocking()" and "set_blocking()" functions allow getting and
setting a file descriptor’s blocking mode ("O_NONBLOCK".) (Contributed
by Victor Stinner in bpo-22054.)

The "truncate()" and "ftruncate()" functions are now supported on
Windows.  (Contributed by Steve Dower in bpo-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:

   >>> os.path.commonprefix(['/usr/lib', '/usr/local/lib'])
   '/usr/l'

   >>> os.path.commonpath(['/usr/lib', '/usr/local/lib'])
   '/usr'

(Contributed by Rafik Draoui and Serhiy Storchaka in bpo-10395.)


pathlib
-------

The new "Path.samefile()" method can be used to check whether the path
points to the same file as another path, which can be either another
"Path" object, or a string:

   >>> import pathlib
   >>> p1 = pathlib.Path('/etc/hosts')
   >>> p2 = pathlib.Path('/etc/../etc/hosts')
   >>> p1.samefile(p2)
   True

(Contributed by Vajrasky Kok and Antoine Pitrou in bpo-19775.)

The "Path.mkdir()" method now accepts a new optional *exist_ok*
argument to match "mkdir -p" and "os.makedirs()" functionality.
(Contributed by Berker Peksag in bpo-21539.)

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

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

New "Path.write_text()", "Path.read_text()", "Path.write_bytes()",
"Path.read_bytes()" methods to simplify read/write operations on
files.

The following code snippet will create or rewrite existing file
"~/spam42":

   >>> import pathlib
   >>> p = pathlib.Path('~/spam42')
   >>> p.expanduser().write_text('ham')
   3

(Contributed by Christopher Welborn in bpo-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 bpo-23611.)


poplib
------

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


re
--

References and conditional references to groups with fixed length are
now allowed in lookbehind assertions:

   >>> import re
   >>> pat = re.compile(r'(a|b).(?<=\1)c')
   >>> pat.match('aac')
   <_sre.SRE_Match object; span=(0, 3), match='aac'>
   >>> pat.match('bbc')
   <_sre.SRE_Match object; span=(0, 3), match='bbc'>

(Contributed by Serhiy Storchaka in bpo-9179.)

The number of capturing groups in regular expressions is no longer
limited to 100.  (Contributed by Serhiy Storchaka in bpo-22437.)

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

The "re.error" exceptions have new attributes, "msg", "pattern",
"pos", "lineno", and "colno", that provide better context information
about the error:

   >>> re.compile("""
   ...     (?x)
   ...     .++
   ... """)
   Traceback (most recent call last):
      ...
   sre_constants.error: multiple repeat at position 16 (line 3, column 7)

(Contributed by Serhiy Storchaka in bpo-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 bpo-22940.)


selectors
---------

The new "DevpollSelector" supports efficient "/dev/poll" polling on
Solaris. (Contributed by Giampaolo Rodola’ in bpo-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 bpo-19840.)

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


signal
------

On Windows, the "set_wakeup_fd()" function now also supports socket
handles.  (Contributed by Victor Stinner in bpo-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 bpo-21076.)


smtpd
-----

Both the "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 bpo-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 bpo-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 bpo-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 bpo-14758.)


smtplib
-------

A new "SMTP.auth()" method provides a convenient way to implement
custom authentication mechanisms. (Contributed by Milan Oberkirch in
bpo-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 bpo-16914.)

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


sndhdr
------

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


socket
------

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

A new "socket.sendfile()" method allows sending 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
bpo-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 bpo-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 bpo-21455.)


ssl
---


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

(Contributed by Geert Jansen in bpo-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 are 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 bpo-20188.)

Where OpenSSL support is present, the "ssl" module now implements the
*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. The "HAS_ALPN" flag indicates
whether ALPN 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 bpo-20421.)

The "SSLSocket" class now implements a "SSLSocket.sendfile()" method.
(Contributed by Giampaolo Rodola’ in bpo-17552.)

The "SSLSocket.send()" method now raises either the
"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 bpo-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 bpo-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 bpo-23186.)

The "SSLSocket.do_handshake()", "SSLSocket.read()",
"SSLSocket.shutdown()", and "SSLSocket.write()" methods of the
"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 bpo-23853.)

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


sqlite3
-------

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


subprocess
----------

The new "run()" function has been added. It runs the specified command
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 bpo-23342.)

Examples:

   >>> subprocess.run(["ls", "-l"])  # doesn't capture output
   CompletedProcess(args=['ls', '-l'], returncode=0)

   >>> subprocess.run("exit 1", shell=True, check=True)
   Traceback (most recent call last):
     ...
   subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1

   >>> subprocess.run(["ls", "-l", "/dev/null"], stdout=subprocess.PIPE)
   CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
   stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n')


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 bpo-24017.)

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


sysconfig
---------

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


tarfile
-------

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

The "TarFile.extractall()" and "TarFile.extract()" methods now take a
keyword argument *numeric_owner*.  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
bpo-23193.)

The "TarFile.list()" now accepts an optional *members* keyword
argument that can be set to a subset of the list returned by
"TarFile.getmembers()". (Contributed by Serhiy Storchaka in
bpo-21549.)


threading
---------

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


time
----

The "monotonic()" function is now always available. (Contributed by
Victor Stinner in bpo-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 bpo-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 bpo-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 bpo-20035.)


traceback
---------

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

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

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


types
-----

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

A new type called "CoroutineType", which is used for *coroutine*
objects created by "async def" functions. (Contributed by Yury
Selivanov in bpo-24400.)


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

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


unittest
--------

The "TestLoader.loadTestsFromModule()" method now accepts a keyword-
only argument *pattern* which is passed to "load_tests" as the third
argument.  Found packages are now checked for "load_tests" regardless
of whether their path matches *pattern*, because it is impossible for
a package name to match the default pattern. (Contributed by Robert
Collins and Barry A. Warsaw in bpo-16662.)

Unittest discovery errors now are exposed in the "TestLoader.errors"
attribute of the "TestLoader" instance. (Contributed by Robert Collins
in bpo-19746.)

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


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

The "Mock" class has the following improvements:

* The 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 bpo-21238.)

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

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

It is no longer necessary to explicitly pass "create=True" to the
"patch()" function when patching builtin names. (Contributed by Kushal
Das in bpo-17660.)


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 bpo-19494 and Akshit
Khurana in bpo-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 bpo-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 bpo-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
bpo-22118.)


wsgiref
-------

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


xmlrpc
------

The "client.ServerProxy" class now supports the *context manager*
protocol. (Contributed by Claudiu Popa in bpo-20627.)

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


xml.sax
-------

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

"parseString()" now accepts a "str" instance. (Contributed by Serhiy
Storchaka in bpo-10590.)


zipfile
-------

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

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


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

Many functions in the "mmap", "ossaudiodev", "socket", "ssl", and
"codecs" modules now accept writable *bytes-like objects*.
(Contributed by Serhiy Storchaka in bpo-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 bpo-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 bpo-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 bpo-21486, bpo-21487, bpo-20826, bpo-23266.)

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

Many operations on "io.BytesIO" are now 50% to 100% faster.
(Contributed by Serhiy Storchaka in bpo-15381 and David Wilson in
bpo-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 bpo-20416 and
bpo-23344.)

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

Regular expressions are now parsed up to 10% faster. (Contributed by
Serhiy Storchaka in bpo-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 bpo-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 bpo-22540.)

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

Objects from the "random" module now use 50% less memory on 64-bit
builds.  (Contributed by Serhiy Storchaka in bpo-23488.)

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

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

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


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

New "calloc" functions were added:

* "PyMem_RawCalloc()",

* "PyMem_Calloc()",

* "PyObject_Calloc()".

(Contributed by Victor Stinner in bpo-21233.)

New encoding/decoding helper functions:

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

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

(Contributed by Victor Stinner in bpo-18395.)

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

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

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

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

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

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

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

Extension modules now include a 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.


Deprecated Python Behavior
--------------------------

Raising the "StopIteration" exception inside a generator will now
generate a silent "PendingDeprecationWarning", which will become a
non-silent deprecation warning in Python 3.6 and will trigger a
"RuntimeError" in Python 3.7. See PEP 479: Change StopIteration
handling inside generators for details.


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
"http.cookies.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.
(Contributed by Serhiy Storchaka in bpo-23671.)

The "platform.dist()" and "platform.linux_distribution()" functions
are now deprecated.  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 bpo-1322.)

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

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

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

"getargvalues()" and "formatargvalues()" functions were inadvertently
marked as deprecated with the release of Python 3.5.0.

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

Use of unrecognized special sequences consisting of "'\'" and an ASCII
letter in regular expression patterns and replacement patterns now
raises a deprecation warning and will be forbidden in Python 3.6.
(Contributed by Serhiy Storchaka in bpo-23622.)

The undocumented and unofficial *use_load_tests* default argument of
the "unittest.TestLoader.loadTestsFromModule()" method now is
deprecated and ignored. (Contributed by Robert Collins and Barry A.
Warsaw in bpo-16662.)


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
  bpo-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 bpo-23464.)


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

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


Changes in Python behavior
--------------------------

* Due to an oversight, earlier Python versions erroneously accepted
  the following syntax:

     f(1 for x in [1], *args)
     f(1 for x in [1], **kwargs)

  Python 3.5 now correctly raises a "SyntaxError", as generator
  expressions must be put in parentheses if not a sole argument to a
  function.


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 bpo-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 bpo-20951.)

* The "__name__" attribute of generators 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 bpo-21205.)

* The deprecated “strict” mode and argument of "HTMLParser",
  "HTMLParser.error()", and the "HTMLParserError" exception have been
  removed.  (Contributed by Ezio Melotti in bpo-15114.) The
  *convert_charrefs* argument of "HTMLParser" is now "True" by
  default.  (Contributed by Berker Peksag in bpo-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 bpo-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
  (bpo-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 bpo-21793.)

* When an import loader defines
  "importlib.machinery.Loader.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 bpo-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. (Contributed by Serhiy Storchaka in bpo-22818.)

* The "http.cookies.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 bpo-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. sourceless 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 "ssl.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
  bpo-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 the 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 bpo-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 bpo-15582.)

* Nested "functools.partial()" calls are now flattened.  If you were
  relying on the previous behavior, you can now either add an
  attribute to a "functools.partial()" object or you can create a
  subclass of "functools.partial()". (Contributed by Alexander
  Belopolsky in bpo-7830.)


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 bpo-22453.)

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

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


Notable changes in Python 3.5.4
===============================


New "make regen-all" build target
---------------------------------

To simplify cross-compilation, and to ensure that CPython can reliably
be compiled without requiring an existing version of Python to already
be available, the autotools-based build system no longer attempts to
implicitly recompile generated files based on file modification times.

Instead, a new "make regen-all" command has been added to force
regeneration of these files when desired (e.g. after an initial
version of Python has already been built based on the pregenerated
versions).

More selective regeneration targets are also defined - see
Makefile.pre.in for details.

(Contributed by Victor Stinner in bpo-23404.)

Added in version 3.5.4.


Removal of "make touch" build target
------------------------------------

The "make touch" build target previously used to request implicit
regeneration of generated files by updating their modification times
has been removed.

It has been replaced by the new "make regen-all" target.

(Contributed by Victor Stinner in bpo-23404.)

Changed in version 3.5.4.
