whatsnew/3.5: Add some examples
Patch by Elvis Pranskevichus
This commit is contained in:
Yury Selivanov
parent
f07422c025
commit
239503773d
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@ -358,7 +358,7 @@ unpackings::
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PEP 461 - % formatting support for bytes and bytearray
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------------------------------------------------------
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PEP 461 adds support for ``%``
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:pep:`461` adds support for ``%``
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:ref:`interpolation operator <bytes-formatting>` to :class:`bytes`
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and :class:`bytearray`.
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@ -447,15 +447,24 @@ PEP 471 - os.scandir() function -- a better and faster directory iterator
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:pep:`471` adds a new directory iteration function, :func:`os.scandir`,
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to the standard library. Additionally, :func:`os.walk` is now
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implemented using ``os.scandir()``, which makes it 3 to 5 times faster
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implemented using ``scandir``, which makes it 3 to 5 times faster
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on POSIX systems and 7 to 20 times faster on Windows systems. This is
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largely achieved by greatly reducing the number of calls to :func:`os.stat`
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required to walk a directory tree.
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Additionally, ``os.scandir()`` returns an iterator, as opposed to returning
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Additionally, ``scandir`` returns an iterator, as opposed to returning
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a list of file names, which improves memory efficiency when iterating
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over very large directories.
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The following example shows a simple use of :func:`os.scandir` to display all
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the files (excluding directories) in the given *path* that don't start with
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``'.'``. The :meth:`entry.is_file <os.DirEntry.is_file>` call will generally
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not make an additional system call::
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for entry in os.scandir(path):
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if not entry.name.startswith('.') and entry.is_file():
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print(entry.name)
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.. seealso::
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:pep:`471` -- os.scandir() function -- a better and faster directory iterator
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@ -641,6 +650,27 @@ PEP 485: A function for testing approximate equality
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functions which tell whether two values are approximately equal or
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"close" to each other. Whether or not two values are considered
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close is determined according to given absolute and relative tolerances.
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Relative tolerance is the maximum allowed difference between ``isclose()``
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arguments, relative to the larger absolute value::
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>>> import math
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>>> a = 5.0
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>>> b = 4.99998
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>>> math.isclose(a, b, rel_tol=1e-5)
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True
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>>> math.isclose(a, b, rel_tol=1e-6)
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False
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It is also possible to compare two values using absolute tolerance, which
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must be a non-negative value::
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>>> import math
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>>> a = 5.0
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>>> b = 4.99998
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>>> math.isclose(a, b, abs_tol=0.00003)
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True
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>>> math.isclose(a, b, abs_tol=0.00001)
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False
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.. seealso::
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@ -678,6 +708,13 @@ Some smaller changes made to the core Python language are:
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New Modules
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===========
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typing
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------
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The new :mod:`typing` :term:`provisional <provisional api>` module
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provides standard definitions and tools for function type annotations.
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See :ref:`Type Hints <whatsnew-pep-484>` for more information.
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.. _whatsnew-zipapp:
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zipapp
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@ -854,8 +891,25 @@ configparser
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------------
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Config parsers can be customized by providing a dictionary of converters in the
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constructor. All converters defined in config parser (either by subclassing or
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constructor, or All converters defined in config parser (either by subclassing or
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by providing in a constructor) will be available on all section proxies.
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Example::
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>>> import configparser
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>>> conv = {}
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>>> conv['list'] = lambda v: [e.strip() for e in v.split() if e.strip()]
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>>> cfg = configparser.ConfigParser(converters=conv)
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>>> cfg.read_string("""
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... [s]
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... list = a b c d e f g
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... """)
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>>> cfg.get('s', 'list')
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'a b c d e f g'
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>>> cfg.getlist('s', 'list')
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['a', 'b', 'c', 'd', 'e', 'f', 'g']
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(Contributed by Łukasz Langa in :issue:`18159`.)
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@ -865,8 +919,17 @@ contextlib
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The new :func:`~contextlib.redirect_stderr` context manager (similar to
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:func:`~contextlib.redirect_stdout`) makes it easier for utility scripts to
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handle inflexible APIs that write their output to :data:`sys.stderr` and
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don't provide any options to redirect it. (Contributed by Berker Peksag in
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:issue:`22389`.)
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don't provide any options to redirect it::
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>>> import contextlib, io, logging
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>>> f = io.StringIO()
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>>> with contextlib.redirect_stderr(f):
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... logging.warning('warning')
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...
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>>> f.getvalue()
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'WARNING:root:warning\n'
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(Contributed by Berker Peksag in :issue:`22389`.)
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curses
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@ -1001,9 +1064,19 @@ heapq
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-----
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Element comparison in :func:`~heapq.merge` can now be customized by
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passing a :term:`key function` in a new optional *key* keyword argument.
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A new optional *reverse* keyword argument can be used to reverse element
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comparison. (Contributed by Raymond Hettinger in :issue:`13742`.)
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passing a :term:`key function` in a new optional *key* keyword argument,
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and a new optional *reverse* keyword argument can be used to reverse element
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comparison::
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>>> import heapq
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>>> a = ['9', '777', '55555']
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>>> b = ['88', '6666']
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>>> list(heapq.merge(a, b, key=len))
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['9', '88', '777', '6666', '55555']
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>>> list(heapq.merge(reversed(a), reversed(b), key=len, reverse=True))
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['55555', '6666', '777', '88', '9']
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(Contributed by Raymond Hettinger in :issue:`13742`.)
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http
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@ -1022,7 +1095,17 @@ now raises a :exc:`~http.client.RemoteDisconnected` exception when a
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remote server connection is closed unexpectedly. Additionally, if a
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:exc:`ConnectionError` (of which ``RemoteDisconnected``
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is a subclass) is raised, the client socket is now closed automatically,
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and will reconnect on the next request.
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and will reconnect on the next request::
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import http.client
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conn = http.client.HTTPConnection('www.python.org')
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for retries in range(3):
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try:
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conn.request('GET', '/')
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resp = conn.getresponse()
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except http.client.RemoteDisconnected:
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pass
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(Contributed by Martin Panter in :issue:`3566`.)
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@ -1095,7 +1178,14 @@ and :issue:`20334`.)
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A new
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:meth:`BoundArguments.apply_defaults <inspect.BoundArguments.apply_defaults>`
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method provides a way to set default values for missing arguments.
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method provides a way to set default values for missing arguments::
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>>> def foo(a, b='ham', *args): pass
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>>> ba = inspect.signature(foo).bind('spam')
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>>> ba.apply_defaults()
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>>> ba.arguments
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OrderedDict([('a', 'spam'), ('b', 'ham'), ('args', ())])
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(Contributed by Yury Selivanov in :issue:`24190`.)
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A new class method
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@ -1137,12 +1227,28 @@ ipaddress
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Both :class:`~ipaddress.IPv4Network` and :class:`~ipaddress.IPv6Network` classes
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now accept an ``(address, netmask)`` tuple argument, so as to easily construct
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network objects from existing addresses. (Contributed by Peter Moody
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and Antoine Pitrou in :issue:`16531`.)
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network objects from existing addresses::
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>>> import ipaddress
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>>> ipaddress.IPv4Network(('127.0.0.0', 8))
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IPv4Network('127.0.0.0/8')
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>>> ipaddress.IPv4Network(('127.0.0.0', '255.0.0.0'))
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IPv4Network('127.0.0.0/8')
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(Contributed by Peter Moody and Antoine Pitrou in :issue:`16531`.)
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A new :attr:`~ipaddress.IPv4Network.reverse_pointer>` attribute for
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:class:`~ipaddress.IPv4Network` and :class:`~ipaddress.IPv6Network` classes
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returns the name of the reverse DNS PTR record.
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returns the name of the reverse DNS PTR record::
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>>> import ipaddress
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>>> addr = ipaddress.IPv4Address('127.0.0.1')
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>>> addr.reverse_pointer
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'1.0.0.127.in-addr.arpa'
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>>> addr6 = ipaddress.IPv6Address('::1')
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>>> addr6.reverse_pointer
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'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'
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(Contributed by Leon Weber in :issue:`20480`.)
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@ -1173,7 +1279,18 @@ locale
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------
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A new :func:`~locale.delocalize` function can be used to convert a string into
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a normalized number string, taking the ``LC_NUMERIC`` settings into account.
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a normalized number string, taking the ``LC_NUMERIC`` settings into account::
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>>> import locale
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>>> locale.setlocale(locale.LC_NUMERIC, 'de_DE.UTF-8')
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'de_DE.UTF-8'
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>>> locale.delocalize('1.234,56')
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'1234.56'
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>>> locale.setlocale(locale.LC_NUMERIC, 'en_US.UTF-8')
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'en_US.UTF-8'
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>>> locale.delocalize('1,234.56')
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'1234.56'
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(Contributed by Cédric Krier in :issue:`13918`.)
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@ -1223,9 +1340,9 @@ Storchaka in :issue:`22486`.)
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multiprocessing
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---------------
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:func:`~multiprocessing.synchronized` objects now support the
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:term:`context manager` protocol. (Contributed by Charles-François Natali in
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:issue:`21565`.)
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:func:`sharedctypes.synchronized <multiprocessing.sharedctypes.synchronized>`
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objects now support the :term:`context manager` protocol.
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(Contributed by Charles-François Natali in :issue:`21565`.)
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operator
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@ -1271,7 +1388,15 @@ on Windows. (Contributed by Steve Dower in :issue:`23668`.)
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There is a new :func:`os.path.commonpath` function returning the longest
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common sub-path of each passed pathname. Unlike the
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:func:`os.path.commonprefix` function, it always returns a valid
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path. (Contributed by Rafik Draoui and Serhiy Storchaka in :issue:`10395`.)
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path::
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>>> os.path.commonprefix(['/usr/lib', '/usr/local/lib'])
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'/usr/l'
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>>> os.path.commonpath(['/usr/lib', '/usr/local/lib'])
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'/usr'
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(Contributed by Rafik Draoui and Serhiy Storchaka in :issue:`10395`.)
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pathlib
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@ -1324,7 +1449,15 @@ re
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--
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References and conditional references to groups with fixed length are now
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allowed in lookbehind assertions.
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allowed in lookbehind assertions::
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>>> import re
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>>> pat = re.compile(r'(a|b).(?<=\1)c')
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>>> pat.match('aac')
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<_sre.SRE_Match object; span=(0, 3), match='aac'>
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>>> pat.match('bbc')
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<_sre.SRE_Match object; span=(0, 3), match='bbc'>
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(Contributed by Serhiy Storchaka in :issue:`9179`.)
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The number of capturing groups in regular expression is no longer limited by
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@ -1338,7 +1471,16 @@ The :class:`re.error` exceptions have new attributes:
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:attr:`~re.error.msg`, :attr:`~re.error.pattern`,
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:attr:`~re.error.pos`, :attr:`~re.error.lineno`,
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and :attr:`~re.error.colno` that provide better context
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information about the error.
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information about the error::
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>>> re.compile("""
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... (?x)
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... .++
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... """)
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Traceback (most recent call last):
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...
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sre_constants.error: multiple repeat at position 16 (line 3, column 7)
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(Contributed by Serhiy Storchaka in :issue:`22578`.)
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@ -1568,6 +1710,20 @@ to invoking subprocesses in Python code that does not need to maintain
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compatibility with earlier Python versions.
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(Contributed by Thomas Kluyver in :issue:`23342`.)
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Examples::
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>>> subprocess.run(["ls", "-l"]) # doesn't capture output
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CompletedProcess(args=['ls', '-l'], returncode=0)
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>>> subprocess.run("exit 1", shell=True, check=True)
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Traceback (most recent call last):
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...
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subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1
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>>> subprocess.run(["ls", "-l", "/dev/null"], stdout=subprocess.PIPE)
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CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
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stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n')
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sys
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---
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