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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.

.. seealso::

    :pep:`478` - Python 3.5 Release Schedule

Summary -- Release highlights

New syntax features:

New library modules:

New built-in features:

CPython implementation improvements:

Significant improvements in the standard library:

Security improvements:

  • SSLv3 is now disabled throughout the standard library. It can still be enabled by instantiating a :class:`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 :ref:`using-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 :term:`awaitable objects <awaitable>`, :term:`coroutine functions <coroutine function>`, :term:`asynchronous iteration <asynchronous iterable>`, and :term:`asynchronous context managers <asynchronous context manager>`.

Coroutine functions are declared using the new :keyword:`async def` syntax:

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

Inside a coroutine function, the new :keyword:`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 :term:`awaitable` protocol by defining the :meth:`__await__` method.

PEP 492 also adds :keyword:`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 :keyword:`async for` and :keyword:`async with` can only be used inside a coroutine function declared with :keyword:`async def`.

Coroutine functions are intended to be run inside a compatible event loop, such as the :ref:`asyncio loop <asyncio-event-loop>`.

Note

.. versionchanged:: 3.5.2
   Starting with CPython 3.5.2, ``__aiter__`` can directly return
   :term:`asynchronous iterators <asynchronous iterator>`.  Returning
   an :term:`awaitable` object will result in a
   :exc:`PendingDeprecationWarning`.

   See more details in the :ref:`async-iterators` documentation
   section.
.. seealso::

   :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 :meth:`__matmul__`, :meth:`__rmatmul__`, and :meth:`__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.])
.. seealso::

   :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 :ref:`function calls <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 :ref:`exprlists` and :ref:`dict`):

>>> *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}
.. seealso::

   :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 % :ref:`interpolation operator <bytes-formatting>` to :class:`bytes` and :class:`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.

.. seealso::

   :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 :term:`provisional module <provisional API>` 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 :attr:`__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 :class:`~typing.Any` which is consistent with (i.e. assignable to and from) all types.

.. seealso::

   * :mod:`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, :func:`os.scandir`, to the standard library. Additionally, :func:`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 :func:`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 :func:`os.scandir` to display all the files (excluding directories) in the given path that don't start with '.'. The :meth:`entry.is_file() <os.DirEntry.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)
.. seealso::

   :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 :py:const:`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 :exc:`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 :exc:`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:

.. seealso::

   :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 :exc:`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 :exc:`RuntimeError` before it exits the generator frame. The main goal of this change is to ease debugging in the situation where an unguarded :func:`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 :term:`__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 :exc:`PendingDeprecationWarning` will be raised whenever a :exc:`StopIteration` exception is raised inside a generator.

.. seealso::

   :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 :func:`math.isclose` and :func:`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
.. seealso::

   :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.

.. seealso::

    :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 :option:`-O` or :option:`-OO`. Consequently, bytecode files generated from :option:`-O`, and :option:`-OO` may now exist simultaneously. :func:`importlib.util.cache_from_source` has an updated API to help with this change.

.. seealso::

   :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.

.. seealso::

   :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:

New Modules

typing

The new :mod:`typing` :term:`provisional <provisional API>` module provides standard definitions and tools for function type annotations. See :ref:`Type Hints <whatsnew-pep-484>` for more information.

zipapp

The new :mod:`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`.

.. seealso::

   :pep:`441` -- Improving Python ZIP Application Support

Improved Modules

argparse

The :class:`~argparse.ArgumentParser` class now allows disabling :ref:`abbreviated usage <prefix-matching>` of long options by setting :ref:`allow_abbrev` to False. (Contributed by Jonathan Paugh, Steven Bethard, paul j3 and Daniel Eriksson in :issue:`14910`.)

asyncio

Since the :mod:`asyncio` module is :term:`provisional <provisional API>`, all changes introduced in Python 3.5 have also been backported to Python 3.4.x.

Notable changes in the :mod:`asyncio` module since Python 3.4.0:

Updates in 3.5.1:

Updates in 3.5.2:

bz2

The :meth:`BZ2Decompressor.decompress <bz2.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 :class:`~cgi.FieldStorage` class now supports the :term:`context manager` protocol. (Contributed by Berker Peksag in :issue:`20289`.)

cmath

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

code

The :func:`InteractiveInterpreter.showtraceback() <code.InteractiveInterpreter.showtraceback>` method now prints the full chained traceback, just like the interactive interpreter. (Contributed by Claudiu Popa in :issue:`17442`.)

collections

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

:meth:`OrderedDict.items() <collections.OrderedDict.items>`, :meth:`OrderedDict.keys() <collections.OrderedDict.keys>`, :meth:`OrderedDict.values() <collections.OrderedDict.values>` views now support :func:`reversed` iteration. (Contributed by Serhiy Storchaka in :issue:`19505`.)

The :class:`~collections.deque` class now defines :meth:`~collections.deque.index`, :meth:`~collections.deque.insert`, and :meth:`~collections.deque.copy`, and supports the + and * operators. This allows deques to be recognized as a :class:`~collections.abc.MutableSequence` and improves their substitutability for lists. (Contributed by Raymond Hettinger in :issue:`23704`.)

Docstrings produced by :func:`~collections.namedtuple` can now be updated:

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

(Contributed by Berker Peksag in :issue:`24064`.)

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

collections.abc

The :meth:`Sequence.index() <collections.abc.Sequence.index>` method now accepts start and stop arguments to match the corresponding methods of :class:`tuple`, :class:`list`, etc. (Contributed by Devin Jeanpierre in :issue:`23086`.)

A new :class:`~collections.abc.Generator` abstract base class. (Contributed by Stefan Behnel in :issue:`24018`.)

New :class:`~collections.abc.Awaitable`, :class:`~collections.abc.Coroutine`, :class:`~collections.abc.AsyncIterator`, and :class:`~collections.abc.AsyncIterable` abstract base classes. (Contributed by Yury Selivanov in :issue:`24184`.)

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

compileall

A new :mod:`compileall` option, :samp:`-j {N}`, allows running N workers simultaneously to perform parallel bytecode compilation. The :func:`~compileall.compile_dir` function has a corresponding workers parameter. (Contributed by Claudiu Popa in :issue:`16104`.)

Another new option, -r, allows controlling the maximum recursion level for subdirectories. (Contributed by Claudiu Popa in :issue:`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 :func:`~compileall.compile_dir`, :func:`~compileall.compile_file`, and :func:`~compileall.compile_path` can now accept an integer value indicating the level of output suppression. (Contributed by Thomas Kluyver in :issue:`21338`.)

concurrent.futures

The :meth:`Executor.map() <concurrent.futures.Executor.map>` method now accepts a chunksize argument to allow batching of tasks to improve performance when :meth:`~concurrent.futures.ProcessPoolExecutor` is used. (Contributed by Dan O'Reilly in :issue:`11271`.)

The number of workers in the :class:`~concurrent.futures.ThreadPoolExecutor` constructor is optional now. The default value is 5 times the number of CPUs. (Contributed by Claudiu Popa in :issue:`21527`.)

configparser

:mod:`configparser` now provides a way to customize the conversion of values by specifying a dictionary of converters in the :class:`~configparser.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 :issue:`18159`.)

contextlib

The new :func:`~contextlib.redirect_stderr` :term:`context manager` (similar to :func:`~contextlib.redirect_stdout`) makes it easier for utility scripts to handle inflexible APIs that write their output to :data:`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 :issue:`22389`.)

csv

The :meth:`~csv.csvwriter.writerow` method now supports arbitrary iterables, not just sequences. (Contributed by Serhiy Storchaka in :issue:`23171`.)

curses

The new :func:`~curses.update_lines_cols` function updates the :data:`LINES` and :data:`COLS` module variables. This is useful for detecting manual screen resizing. (Contributed by Arnon Yaari in :issue:`4254`.)

dbm

:func:`dumb.open <dbm.dumb.open>` always creates a new database when the flag has the value "n". (Contributed by Claudiu Popa in :issue:`18039`.)

difflib

The charset of HTML documents generated by :meth:`HtmlDiff.make_file() <difflib.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 :func:`~difflib.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 the 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 :mod:`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 :func:`~doctest.DocTestSuite` function returns an empty :class:`unittest.TestSuite` if module contains no docstrings, instead of raising :exc:`ValueError`. (Contributed by Glenn Jones in :issue:`15916`.)

email

A new policy option :attr:`Policy.mangle_from_ <email.policy.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 :attr:`~email.policy.compat32` and False for all other policies. (Contributed by Milan Oberkirch in :issue:`20098`.)

A new :meth:`Message.get_content_disposition() <email.message.Message.get_content_disposition>` method provides easy access to a canonical value for the :mailheader:`Content-Disposition` header. (Contributed by Abhilash Raj in :issue:`21083`.)

A new policy option :attr:`EmailPolicy.utf8 <email.policy.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`.)

The :class:`mime.text.MIMEText <email.mime.text.MIMEText>` constructor now accepts a :class:`charset.Charset <email.charset.Charset>` instance. (Contributed by Claude Paroz and Berker Peksag in :issue:`16324`.)

enum

The :class:`~enum.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

The :func:`~faulthandler.enable`, :func:`~faulthandler.register`, :func:`~faulthandler.dump_traceback` and :func:`~faulthandler.dump_traceback_later` functions now accept file descriptors in addition to file-like objects. (Contributed by Wei Wu in :issue:`23566`.)

functools

Most of the :func:`~functools.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

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

gzip

The mode argument of the :class:`~gzip.GzipFile` constructor now accepts "x" to request exclusive creation. (Contributed by Tim Heaney in :issue:`19222`.)

heapq

Element comparison in :func:`~heapq.merge` can now be customized by passing a :term:`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 :issue:`13742`.)

http

A new :class:`HTTPStatus <http.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`.)

http.client

:meth:`HTTPConnection.getresponse() <http.client.HTTPConnection.getresponse>` now raises a :exc:`~http.client.RemoteDisconnected` exception when a remote server connection is closed unexpectedly. Additionally, if a :exc:`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 :issue:`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 :file:`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 :menuselection:`Help --> About IDLE` dialog.

imaplib

The :class:`~imaplib.IMAP4` class now supports the :term:`context manager` protocol. When used in a :keyword:`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 :mod:`imaplib` module now supports RFC 5161 (ENABLE Extension) and RFC 6855 (UTF-8 Support) via the :meth:`IMAP4.enable() <imaplib.IMAP4.enable>` method. A new :attr:`IMAP4.utf8_enabled <imaplib.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 :mod:`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 :func:`~imghdr.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 :class:`util.LazyLoader <importlib.util.LazyLoader>` class allows for lazy loading of modules in applications where startup time is important. (Contributed by Brett Cannon in :issue:`17621`.)

The :func:`abc.InspectLoader.source_to_code() <importlib.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 :func:`util.module_from_spec() <importlib.util.module_from_spec>` function is now the preferred way to create a new module. As opposed to creating a :class:`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 the :class:`~inspect.Signature` and :class:`~inspect.Parameter` classes are now picklable and hashable. (Contributed by Yury Selivanov in :issue:`20726` and :issue:`20334`.)

A new :meth:`BoundArguments.apply_defaults() <inspect.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 :issue:`24190`.)

A new class method :meth:`Signature.from_callable() <inspect.Signature.from_callable>` makes subclassing of :class:`~inspect.Signature` easier. (Contributed by Yury Selivanov and Eric Snow in :issue:`17373`.)

The :func:`~inspect.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 :term:`coroutine functions <coroutine function>` and :term:`coroutine objects <coroutine>` has been added: :func:`~inspect.iscoroutine`, :func:`~inspect.iscoroutinefunction`, :func:`~inspect.isawaitable`, :func:`~inspect.getcoroutinelocals`, and :func:`~inspect.getcoroutinestate`. (Contributed by Yury Selivanov in :issue:`24017` and :issue:`24400`.)

The :func:`~inspect.stack`, :func:`~inspect.trace`, :func:`~inspect.getouterframes`, and :func:`~inspect.getinnerframes` functions now return a list of named tuples. (Contributed by Daniel Shahaf in :issue:`16808`.)

io

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

ipaddress

Both the :class:`~ipaddress.IPv4Network` and :class:`~ipaddress.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 :issue:`16531`.)

A new :attr:`~ipaddress.IPv4Network.reverse_pointer` attribute for the :class:`~ipaddress.IPv4Network` and :class:`~ipaddress.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 :issue:`20480`.)

json

The :mod:`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 :exc:`~json.JSONDecodeError` instead of :exc:`ValueError` to provide better context information about the error. (Contributed by Serhiy Storchaka in :issue:`19361`.)

linecache

A new :func:`~linecache.lazycache` function can be used to capture information about a non-file-based module to permit getting its lines later via :func:`~linecache.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 :issue:`17911`.)

locale

A new :func:`~locale.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 :issue:`13918`.)

logging

All logging methods (:class:`~logging.Logger` :meth:`~logging.Logger.log`, :meth:`~logging.Logger.exception`, :meth:`~logging.Logger.critical`, :meth:`~logging.Logger.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 :issue:`20537`.)

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

The :class:`handlers.QueueListener <logging.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 :meth:`LZMADecompressor.decompress() <lzma.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 :mod:`math` module: :data:`~math.inf` and :data:`~math.nan`. (Contributed by Mark Dickinson in :issue:`23185`.)

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

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

multiprocessing

:func:`sharedctypes.synchronized() <multiprocessing.sharedctypes.synchronized>` objects now support the :term:`context manager` protocol. (Contributed by Charles-François Natali in :issue:`21565`.)

operator

:func:`~operator.attrgetter`, :func:`~operator.itemgetter`, and :func:`~operator.methodcaller` objects now support pickling. (Contributed by Josh Rosenberg and Serhiy Storchaka in :issue:`22955`.)

New :func:`~operator.matmul` and :func:`~operator.imatmul` functions to perform matrix multiplication. (Contributed by Benjamin Peterson in :issue:`21176`.)

os

The new :func:`~os.scandir` function returning an iterator of :class:`~os.DirEntry` objects has been added. If possible, :func:`~os.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 :attr:`stat_result.st_file_attributes <os.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 :issue:`21719`.)

The :func:`~os.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 :issue:`22181`.)

New :func:`~os.get_blocking` and :func:`~os.set_blocking` functions allow getting and setting a file descriptor's blocking mode (:const:`~os.O_NONBLOCK`.) (Contributed by Victor Stinner in :issue:`22054`.)

The :func:`~os.truncate` and :func:`~os.ftruncate` functions are now supported on Windows. (Contributed by Steve Dower in :issue:`23668`.)

There is a new :func:`os.path.commonpath` function returning the longest common sub-path of each passed pathname. Unlike the :func:`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 :issue:`10395`.)

pathlib

The new :meth:`Path.samefile() <pathlib.Path.samefile>` method can be used to check whether the path points to the same file as another path, which can be either another :class:`~pathlib.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 :issue:`19775`.)

The :meth:`Path.mkdir() <pathlib.Path.mkdir>` method now accepts a new optional exist_ok argument to match mkdir -p and :func:`os.makedirs` functionality. (Contributed by Berker Peksag in :issue:`21539`.)

There is a new :meth:`Path.expanduser() <pathlib.Path.expanduser>` method to expand ~ and ~user prefixes. (Contributed by Serhiy Storchaka and Claudiu Popa in :issue:`19776`.)

A new :meth:`Path.home() <pathlib.Path.home>` class method can be used to get a :class:`~pathlib.Path` instance representing the user’s home directory. (Contributed by Victor Salgado and Mayank Tripathi in :issue:`19777`.)

New :meth:`Path.write_text() <pathlib.Path.write_text>`, :meth:`Path.read_text() <pathlib.Path.read_text>`, :meth:`Path.write_bytes() <pathlib.Path.write_bytes>`, :meth:`Path.read_bytes() <pathlib.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 :issue:`20218`.)

pickle

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

poplib

A new :meth:`POP3.utf8() <poplib.POP3.utf8>` command enables RFC 6856 (Internationalized Email) support, if a POP server supports it. (Contributed by Milan OberKirch in :issue:`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 :issue:`9179`.)

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

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

The :class:`re.error` exceptions have new attributes, :attr:`~re.error.msg`, :attr:`~re.error.pattern`, :attr:`~re.error.pos`, :attr:`~re.error.lineno`, and :attr:`~re.error.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 :issue:`22578`.)

readline

A new :func:`~readline.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 :class:`~selectors.DevpollSelector` supports efficient /dev/poll polling on Solaris. (Contributed by Giampaolo Rodola' in :issue:`18931`.)

shutil

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

The :func:`~shutil.make_archive` function now supports the xztar format. (Contributed by Serhiy Storchaka in :issue:`5411`.)

signal

On Windows, the :func:`~signal.set_wakeup_fd` function now also supports socket handles. (Contributed by Victor Stinner in :issue:`22018`.)

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

smtpd

Both the :class:`~smtpd.SMTPServer` and :class:`~smtpd.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 :meth:`SMTPServer.process_message() <smtpd.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 :class:`~smtpd.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 :meth:`SMTPServer.process_message() <smtpd.SMTPServer.process_message>` via the mail_options keyword. (Contributed by Milan Oberkirch and R. David Murray in :issue:`21795`.)

The :class:`~smtpd.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 :meth:`SMTPServer.process_message() <smtpd.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 :class:`~smtpd.SMTPServer` constructor, and have it successfully connect. (Contributed by Milan Oberkirch in :issue:`14758`.)

smtplib

A new :meth:`SMTP.auth() <smtplib.SMTP.auth>` method provides a convenient way to implement custom authentication mechanisms. (Contributed by Milan Oberkirch in :issue:`15014`.)

The :meth:`SMTP.set_debuglevel() <smtplib.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 the :meth:`SMTP.sendmail() <smtplib.SMTP.sendmail>` and :meth:`SMTP.send_message() <smtplib.SMTP.send_message>` methods now support RFC 6531 (SMTPUTF8). (Contributed by Milan Oberkirch and R. David Murray in :issue:`22027`.)

sndhdr

The :func:`~sndhdr.what` and :func:`~sndhdr.whathdr` functions now return a :func:`~collections.namedtuple`. (Contributed by Claudiu Popa in :issue:`18615`.)

socket

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

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

The :meth:`socket.sendall() <socket.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 :meth:`socket.listen() <socket.socket.listen>` method is now optional. By default it is set to :data:`SOMAXCONN <socket.SOMAXCONN>` or to 128, whichever is less. (Contributed by Charles-François Natali in :issue:`21455`.)

ssl

Memory BIO Support

(Contributed by Geert Jansen in :issue:`21965`.)

The new :class:`~ssl.SSLObject` class has been added to provide SSL protocol support for cases when the network I/O capabilities of :class:`~ssl.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 :class:`~ssl.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 :class:`~ssl.SSLSocket`'s readiness model ("select/poll") is inefficient.

A new :meth:`SSLContext.wrap_bio() <ssl.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, the :mod:`ssl` module now implements the Application-Layer Protocol Negotiation TLS extension as described in RFC 7301.

The new :meth:`SSLContext.set_alpn_protocols() <ssl.SSLContext.set_alpn_protocols>` can be used to specify which protocols a socket should advertise during the TLS handshake.

The new :meth:`SSLSocket.selected_alpn_protocol() <ssl.SSLSocket.selected_alpn_protocol>` returns the protocol that was selected during the TLS handshake. The :const:`~ssl.HAS_ALPN` flag indicates whether ALPN support is present.

Other Changes

There is a new :meth:`SSLSocket.version() <ssl.SSLSocket.version>` method to query the actual protocol version in use. (Contributed by Antoine Pitrou in :issue:`20421`.)

The :class:`~ssl.SSLSocket` class now implements a :meth:`SSLSocket.sendfile() <ssl.SSLSocket.sendfile>` method. (Contributed by Giampaolo Rodola' in :issue:`17552`.)

The :meth:`SSLSocket.send() <ssl.SSLSocket.send>` method now raises either the :exc:`ssl.SSLWantReadError` or :exc:`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 :func:`~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 :class:`int`. (Contributed by Akira Li in :issue:`19940`.)

New :meth:`SSLObject.shared_ciphers() <ssl.SSLObject.shared_ciphers>` and :meth:`SSLSocket.shared_ciphers() <ssl.SSLSocket.shared_ciphers>` methods return the list of ciphers sent by the client during the handshake. (Contributed by Benjamin Peterson in :issue:`23186`.)

The :meth:`SSLSocket.do_handshake() <ssl.SSLSocket.do_handshake>`, :meth:`SSLSocket.read() <ssl.SSLSocket.read>`, :meth:`SSLSocket.shutdown() <ssl.SSLSocket.shutdown>`, and :meth:`SSLSocket.write() <ssl.SSLSocket.write>` methods of the :class:`~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 :func:`~ssl.match_hostname` function now supports matching of IP addresses. (Contributed by Antoine Pitrou in :issue:`23239`.)

sqlite3

The :class:`~sqlite3.Row` class now fully supports the sequence protocol, in particular :func:`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 :func:`~subprocess.run` function has been added. It runs the specified command and returns a :class:`~subprocess.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`.)

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 :func:`~sys.set_coroutine_wrapper` function allows setting a global hook that will be called whenever a :term:`coroutine object <coroutine>` is created by an :keyword:`async def` function. A corresponding :func:`~sys.get_coroutine_wrapper` can be used to obtain a currently set wrapper. Both functions are :term:`provisional <provisional API>`, and are intended for debugging purposes only. (Contributed by Yury Selivanov in :issue:`24017`.)

A new :func:`~sys.is_finalizing` function can be used to check if the Python interpreter is :term:`shutting down <interpreter shutdown>`. (Contributed by Antoine Pitrou in :issue:`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 :issue:`23437`.)

tarfile

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

The :meth:`TarFile.extractall() <tarfile.TarFile.extractall>` and :meth:`TarFile.extract() <tarfile.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 :issue:`23193`.)

The :meth:`TarFile.list() <tarfile.TarFile.list>` now accepts an optional members keyword argument that can be set to a subset of the list returned by :meth:`TarFile.getmembers() <tarfile.TarFile.getmembers>`. (Contributed by Serhiy Storchaka in :issue:`21549`.)

threading

Both the :meth:`Lock.acquire() <threading.Lock.acquire>` and :meth:`RLock.acquire() <threading.RLock.acquire>` methods now use a monotonic clock for timeout management. (Contributed by Victor Stinner in :issue:`22043`.)

time

The :func:`~time.monotonic` function is now always available. (Contributed by Victor Stinner in :issue:`22043`.)

timeit

A new command line option -u or :samp:`--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 :func:`~timeit.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 :mod:`tkinter._fix` module used for setting up the Tcl/Tk environment on Windows has been replaced by a private function in the :mod:`_tkinter` module which makes no permanent changes to environment variables. (Contributed by Zachary Ware in :issue:`20035`.)

traceback

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

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

Both the :func:`~traceback.print_tb` and :func:`~traceback.print_stack` functions now support negative values for the limit argument. (Contributed by Dmitry Kazakov in :issue:`22619`.)

types

A new :func:`~types.coroutine` function to transform :term:`generator <generator iterator>` and :class:`generator-like <collections.abc.Generator>` objects into :term:`awaitables <awaitable>`. (Contributed by Yury Selivanov in :issue:`24017`.)

A new type called :class:`~types.CoroutineType`, which is used for :term:`coroutine` objects created by :keyword:`async def` functions. (Contributed by Yury Selivanov in :issue:`24400`.)

unicodedata

The :mod:`unicodedata` module now uses data from Unicode 8.0.0.

unittest

The :meth:`TestLoader.loadTestsFromModule() <unittest.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 :issue:`16662`.)

Unittest discovery errors now are exposed in the :data:`TestLoader.errors <unittest.TestLoader.errors>` attribute of the :class:`~unittest.TestLoader` instance. (Contributed by Robert Collins in :issue:`19746`.)

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

unittest.mock

The :class:`~unittest.mock.Mock` class has the following improvements:

The :class:`~unittest.mock.MagicMock` class now supports :meth:`__truediv__`, :meth:`__divmod__` and :meth:`__matmul__` operators. (Contributed by Johannes Baiter in :issue:`20968`, and Håkan Lövdahl in :issue:`23581` and :issue:`23568`.)

It is no longer necessary to explicitly pass create=True to the :func:`~unittest.mock.patch` function when patching builtin names. (Contributed by Kushal Das in :issue:`17660`.)

urllib

A new :class:`request.HTTPPasswordMgrWithPriorAuth <urllib.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 :func:`parse.urlencode() <urllib.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 :func:`request.urlopen() <urllib.request.urlopen>` function accepts an :class:`ssl.SSLContext` object as a context argument, which will be used for the HTTPS connection. (Contributed by Alex Gaynor in :issue:`22366`.)

The :func:`parse.urljoin() <urllib.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`.)

wsgiref

The headers argument of the :class:`headers.Headers <wsgiref.headers.Headers>` class constructor is now optional. (Contributed by Pablo Torres Navarrete and SilentGhost in :issue:`5800`.)

xmlrpc

The :class:`client.ServerProxy <xmlrpc.client.ServerProxy>` class now supports the :term:`context manager` protocol. (Contributed by Claudiu Popa in :issue:`20627`.)

The :class:`client.ServerProxy <xmlrpc.client.ServerProxy>` constructor now accepts an optional :class:`ssl.SSLContext` instance. (Contributed by Alex Gaynor in :issue:`22960`.)

xml.sax

SAX parsers now support a character stream of the :class:`xmlreader.InputSource <xml.sax.xmlreader.InputSource>` object. (Contributed by Serhiy Storchaka in :issue:`2175`.)

:func:`~xml.sax.parseString` now accepts a :class:`str` instance. (Contributed by Serhiy Storchaka in :issue:`10590`.)

zipfile

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

The mode argument of :meth:`ZipFile.open() <zipfile.ZipFile.open>` method now accepts "x" to request exclusive creation. (Contributed by Serhiy Storchaka in :issue:`21717`.)

Other module-level changes

Many functions in the :mod:`mmap`, :mod:`ossaudiodev`, :mod:`socket`, :mod:`ssl`, and :mod:`codecs` modules now accept writable :term:`bytes-like objects <bytes-like object>`. (Contributed by Serhiy Storchaka in :issue:`23001`.)

Optimizations

The :func:`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 :func:`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 :mod:`ipaddress` :class:`~ipaddress.IPv4Network` and :class:`~ipaddress.IPv6Network` have been massively sped up, such as :meth:`~ipaddress.IPv4Network.subnets`, :meth:`~ipaddress.IPv4Network.supernet`, :func:`~ipaddress.summarize_address_range`, :func:`~ipaddress.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 :mod:`ipaddress` objects was optimized to produce significantly smaller output. (Contributed by Serhiy Storchaka in :issue:`23133`.)

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

The :func:`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 :func:`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 :c:func:`PyObject_IsInstance` and :c:func:`PyObject_IsSubclass` functions have been sped up in the common case that the second argument has :class:`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 the :mod:`random` module now use 50% less memory on 64-bit builds. (Contributed by Serhiy Storchaka in :issue:`23488`.)

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

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

String methods :meth:`~str.find`, :meth:`~str.rfind`, :meth:`~str.split`, :meth:`~str.partition` and the :keyword:`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:

(Contributed by Victor Stinner in :issue:`21233`.)

New encoding/decoding helper functions:

(Contributed by Victor Stinner in :issue:`18395`.)

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

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

A new :c:data:`PyExc_RecursionError` exception. (Contributed by Georg Brandl in :issue:`19235`.)

New :c:func:`PyModule_FromDefAndSpec`, :c:func:`PyModule_FromDefAndSpec2`, and :c:func:`PyModule_ExecDef` functions introduced by PEP 489 -- multi-phase extension module initialization. (Contributed by Petr Viktorin in :issue:`24268`.)

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

The :c:member:`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 :exc:`StopIteration` exception inside a generator will now generate a silent :exc:`PendingDeprecationWarning`, which will become a non-silent deprecation warning in Python 3.6 and will trigger a :exc:`RuntimeError` in Python 3.7. See :ref:`PEP 479: Change StopIteration handling inside generators <whatsnew-pep-479>` 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 :mod:`formatter` module has now graduated to full deprecation and is still slated for removal in Python 3.6.

The :func:`asyncio.async` function is deprecated in favor of :func:`~asyncio.ensure_future`.

The :mod:`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 :class:`~smtpd.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 :attr:`~http.cookies.Morsel.key`, :attr:`~http.cookies.Morsel.value` and :attr:`~http.cookies.Morsel.coded_value` of :class:`http.cookies.Morsel` objects is deprecated. Use the :meth:`~http.cookies.Morsel.set` method instead. In addition, the undocumented LegalChars parameter of :meth:`~http.cookies.Morsel.set` is deprecated, and is now ignored.

Passing a format string as keyword argument format_string to the :meth:`~string.Formatter.format` method of the :class:`string.Formatter` class has been deprecated. (Contributed by Serhiy Storchaka in :issue:`23671`.)

The :func:`platform.dist` and :func:`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 :issue:`1322`.)

The previously undocumented from_function and from_builtin methods of :class:`inspect.Signature` are deprecated. Use the new :meth:`Signature.from_callable() <inspect.Signature.from_callable>` method instead. (Contributed by Yury Selivanov in :issue:`24248`.)

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

The :mod:`inspect` :func:`~inspect.getfullargspec`, :func:`~inspect.getcallargs`, and :func:`~inspect.formatargspec` functions are deprecated in favor of the :func:`inspect.signature` API. (Contributed by Yury Selivanov in :issue:`20438`.)

:func:`~inspect.getargvalues` and :func:`~inspect.formatargvalues` functions were inadvertently marked as deprecated with the release of Python 3.5.0.

Use of :const:`re.LOCALE` flag with str patterns or :const:`re.ASCII` is now deprecated. (Contributed by Serhiy Storchaka in :issue:`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 :issue:`23622`.)

The undocumented and unofficial use_load_tests default argument of the :meth:`unittest.TestLoader.loadTestsFromModule` method now is deprecated and ignored. (Contributed by Robert Collins and Barry A. Warsaw in :issue:`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 :mod:`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 :mod:`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 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 :exc:`SyntaxError`, as generator expressions must be put in parentheses if not a sole argument to a function.

Changes in the Python API

Changes in the C API

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 :source:`Makefile.pre.in` for details.

(Contributed by Victor Stinner in :issue:`23404`.)

.. versionadded:: 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 :issue:`23404`.)

.. versionchanged:: 3.5.4