mirror of https://github.com/python/cpython
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ReStructuredText
319 lines
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ReStructuredText
****************************
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What's New in Python 2.7
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****************************
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:Author: A.M. Kuchling (amk at amk.ca)
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:Release: |release|
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:Date: |today|
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.. Fix accents on Kristjan Valur Jonsson, Fuerstenau.
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.. $Id$
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Rules for maintenance:
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* Anyone can add text to this document. Do not spend very much time
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on the wording of your changes, because your text will probably
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get rewritten to some degree.
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* The maintainer will go through Misc/NEWS periodically and add
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changes; it's therefore more important to add your changes to
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Misc/NEWS than to this file.
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* This is not a complete list of every single change; completeness
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is the purpose of Misc/NEWS. Some changes I consider too small
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or esoteric to include. If such a change is added to the text,
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I'll just remove it. (This is another reason you shouldn't spend
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too much time on writing your addition.)
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* If you want to draw your new text to the attention of the
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maintainer, add 'XXX' to the beginning of the paragraph or
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section.
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* It's OK to just add a fragmentary note about a change. For
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example: "XXX Describe the transmogrify() function added to the
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socket module." The maintainer will research the change and
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write the necessary text.
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* You can comment out your additions if you like, but it's not
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necessary (especially when a final release is some months away).
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* Credit the author of a patch or bugfix. Just the name is
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sufficient; the e-mail address isn't necessary.
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* It's helpful to add the bug/patch number in a parenthetical comment.
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XXX Describe the transmogrify() function added to the socket
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module.
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(Contributed by P.Y. Developer; :issue:`12345`.)
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This saves the maintainer some effort going through the SVN logs
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when researching a change.
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This article explains the new features in Python 2.7.
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No release schedule has been decided yet for 2.7.
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.. Compare with previous release in 2 - 3 sentences here.
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add hyperlink when the documentation becomes available online.
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.. ========================================================================
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.. Large, PEP-level features and changes should be described here.
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.. Should there be a new section here for 3k migration?
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.. Or perhaps a more general section describing module changes/deprecation?
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.. ========================================================================
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Other Language Changes
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======================
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Some smaller changes made to the core Python language are:
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* The :func:`int` and :func:`long` types gained a ``bit_length``
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method that returns the number of bits necessary to represent
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its argument in binary::
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>>> n = 37
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>>> bin(37)
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'0b100101'
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>>> n.bit_length()
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6
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>>> n = 2**123-1
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>>> n.bit_length()
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123
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>>> (n+1).bit_length()
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124
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(Contributed by Fredrik Johansson and Victor Stinner; :issue:`3439`.)
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* Integers are now stored internally either in base 2**15 or in base
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2**30, the base being determined at build time. Previously, they
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were always stored in base 2**15. Using base 2**30 gives
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significant performance improvements on 64-bit machines, but
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benchmark results on 32-bit machines have been mixed. Therefore,
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the default is to use base 2**30 on 64-bit machines and base 2**15
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on 32-bit machines; on Unix, there's a new configure option
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--enable-big-digits that can be used to override this default.
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Apart from the performance improvements this change should be
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invisible to end users, with one exception: for testing and
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debugging purposes there's a new structseq ``sys.long_info`` that
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provides information about the internal format, giving the number of
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bits per digit and the size in bytes of the C type used to store
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each digit::
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>>> import sys
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>>> sys.long_info
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sys.long_info(bits_per_digit=30, sizeof_digit=4)
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(Contributed by Mark Dickinson; :issue:`4258`.)
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.. ======================================================================
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Optimizations
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-------------
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A few performance enhancements have been added:
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* The garbage collector now performs better when many objects are
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being allocated without deallocating any. A full garbage collection
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pass is only performed when the middle generation has been collected
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10 times and when the number of survivor objects from the middle
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generation exceeds 10% of the number of objects in the oldest
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generation. The second condition was added to reduce the number
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of full garbage collections as the number of objects on the heap grows,
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avoiding quadratic performance when allocating very many objects.
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(Suggested by Martin von Loewis and implemented by Antoine Pitrou;
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:issue:`4074`.)
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* The garbage collector tries to avoid tracking simple containers which
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can't be part of a cycle. As of now, this is true for tuples and dicts
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containing atomic types (such as ints, strings, etc.). Transitively, a dict
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containing tuples of atomic types won't be tracked either. This helps bring
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down the individual cost of each garbage collection, since it decreases the
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number of objects to be considered and traversed by the collector.
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To help diagnosing this optimization, a new function in the :mod:`gc`
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module, :func:`is_tracked`, returns True if a given instance is tracked
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by the garbage collector, False otherwise.
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(Contributed by Antoine Pitrou; :issue:`4688`.)
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.. ======================================================================
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New, Improved, and Deprecated Modules
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=====================================
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As in every release, Python's standard library received a number of
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enhancements and bug fixes. Here's a partial list of the most notable
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changes, sorted alphabetically by module name. Consult the
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:file:`Misc/NEWS` file in the source tree for a more complete list of
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changes, or look through the Subversion logs for all the details.
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* In Distutils, distutils.sdist.add_defaults now uses package_dir and data_files
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to feed MANIFEST.
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* It is not mandatory anymore to store clear text passwords in the
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:file:`.pypirc` file when registering and uploading packages to PyPI. As long
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as the username is present in that file, the :mod:`distutils` package will
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prompt for the password if not present. (Added by tarek, with the initial
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contribution of Nathan Van Gheem; :issue:`4394`.)
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* The :mod:`bz2` module's :class:`BZ2File` now supports the context
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management protocol, so you can write ``with bz2.BZ2File(...) as f: ...``.
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(Contributed by Hagen Fuerstenau; :issue:`3860`.)
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* A new :class:`Counter` class in the :mod:`collections` module is
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useful for tallying data. :class:`Counter` instances behave mostly
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like dictionaries but return zero for missing keys instead of
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raising a :exc:`KeyError`::
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>>> from collections import Counter
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>>> c=Counter()
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>>> for letter in 'here is a sample of english text':
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... c[letter] += 1
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...
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>>> c
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Counter({' ': 6, 'e': 5, 's': 3, 'a': 2, 'i': 2, 'h': 2,
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'l': 2, 't': 2, 'g': 1, 'f': 1, 'm': 1, 'o': 1, 'n': 1,
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'p': 1, 'r': 1, 'x': 1})
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>>> c['e']
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5
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>>> c['z']
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0
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There are two additional :class:`Counter` methods: :meth:`most_common`
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returns the N most common elements and their counts, and :meth:`elements`
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returns an iterator over the contained element, repeating each element
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as many times as its count::
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>>> c.most_common(5)
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[(' ', 6), ('e', 5), ('s', 3), ('a', 2), ('i', 2)]
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>>> c.elements() ->
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'a', 'a', ' ', ' ', ' ', ' ', ' ', ' ',
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'e', 'e', 'e', 'e', 'e', 'g', 'f', 'i', 'i',
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'h', 'h', 'm', 'l', 'l', 'o', 'n', 'p', 's',
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's', 's', 'r', 't', 't', 'x']
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Contributed by Raymond Hettinger; :issue:`1696199`.
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* The :mod:`gzip` module's :class:`GzipFile` now supports the context
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management protocol, so you can write ``with gzip.GzipFile(...) as f: ...``.
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(Contributed by Hagen Fuerstenau; :issue:`3860`.)
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* The :class:`io.FileIO` class now raises an :exc:`OSError` when passed
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an invalid file descriptor. (Implemented by Benjamin Peterson;
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:issue:`4991`.)
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* The :mod:`pydoc` module now has help for the various symbols that Python
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uses. You can now do ``help('<<')`` or ``help('@')``, for example.
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(Contributed by David Laban; :issue:`4739`.)
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* A new function in the :mod:`subprocess` module,
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:func:`check_output`, runs a command with a specified set of arguments
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and returns the command's output as a string if the command runs without
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error, or raises a :exc:`CalledProcessError` exception otherwise.
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::
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>>> subprocess.check_output(['df', '-h', '.'])
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'Filesystem Size Used Avail Capacity Mounted on\n
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/dev/disk0s2 52G 49G 3.0G 94% /\n'
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>>> subprocess.check_output(['df', '-h', '/bogus'])
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...
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subprocess.CalledProcessError: Command '['df', '-h', '/bogus']' returned non-zero exit status 1
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(Contributed by Gregory P. Smith.)
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* The :func:`is_zipfile` function in the :mod:`zipfile` module will now
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accept a file object, in addition to the path names accepted in earlier
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versions. (Contributed by Gabriel Genellina; :issue:`4756`.)
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.. ======================================================================
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.. whole new modules get described in subsections here
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ttk: Themed Widgets for Tk
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--------------------------
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Tcl/Tk 8.5 includes a set of themed widgets that re-implement basic Tk
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widgets but have a more customizable appearance and can therefore more
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closely resemble the native platform's widgets. This widget
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set was originally called Tile, but was renamed to Ttk (for "themed Tk")
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on being added to Tcl/Tck release 8.5.
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XXX write a brief discussion and an example here.
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The :mod:`ttk` module was written by Guilherme Polo and added in
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:issue:`2983`. An alternate version called ``Tile.py``, written by
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Martin Franklin and maintained by Kevin Walzer, was proposed for
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inclusion in :issue:`2618`, but the authors argued that Guilherme
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Polo's work was more comprehensive.
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.. ======================================================================
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Build and C API Changes
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=======================
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Changes to Python's build process and to the C API include:
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* If you use the :file:`.gdbinit` file provided with Python,
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the "pyo" macro in the 2.7 version will now work when the thread being
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debugged doesn't hold the GIL; the macro will now acquire it before printing.
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(Contributed by Victor Stinner; :issue:`3632`.)
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* :cfunc:`Py_AddPendingCall` is now thread safe, letting any
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worker thread submit notifications to the main Python thread. This
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is particularly useful for asynchronous IO operations.
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(Contributed by Kristjan Valur Jonsson; :issue:`4293`.)
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.. ======================================================================
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Port-Specific Changes: Windows
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-----------------------------------
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* The :mod:`msvcrt` module now contains some constants from
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the :file:`crtassem.h` header file:
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:data:`CRT_ASSEMBLY_VERSION`,
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:data:`VC_ASSEMBLY_PUBLICKEYTOKEN`,
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and :data:`LIBRARIES_ASSEMBLY_NAME_PREFIX`.
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(Contributed by David Cournapeau; :issue:`4365`.)
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* The new :cfunc:`_beginthreadex` API is used to start threads, and
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the native thread-local storage functions are now used.
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(Contributed by Kristjan Valur Jonsson; :issue:`3582`.)
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.. ======================================================================
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Port-Specific Changes: Mac OS X
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-----------------------------------
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.. ======================================================================
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Porting to Python 2.7
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=====================
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This section lists previously described changes and other bugfixes
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that may require changes to your code:
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To be written.
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.. ======================================================================
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.. _acks27:
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Acknowledgements
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================
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The author would like to thank the following people for offering
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suggestions, corrections and assistance with various drafts of this
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article: no one yet.
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