cpython/Doc/library/__future__.rst
Georg Brandl 2ee470f7f9 Merged revisions 64722,64729,64753,64845-64846,64849,64871,64880-64882,64885,64888,64897,64900-64901,64915,64926-64929,64938-64941,64944,64961,64966,64973 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk

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  r64722 | georg.brandl | 2008-07-05 12:13:36 +0200 (Sat, 05 Jul 2008) | 4 lines

  #2663: support an *ignore* argument to shutil.copytree(). Patch by Tarek Ziade.

  This is a new feature, but Barry authorized adding it in the beta period.
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  r64729 | mark.dickinson | 2008-07-05 13:33:52 +0200 (Sat, 05 Jul 2008) | 5 lines

  Issue 3188: accept float('infinity') as well as float('inf').  This
  makes the float constructor behave in the same way as specified
  by various other language standards, including C99, IEEE 754r,
  and the IBM Decimal standard.
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  r64753 | gregory.p.smith | 2008-07-06 05:35:58 +0200 (Sun, 06 Jul 2008) | 4 lines

  - Issue #2862: Make int and float freelist management consistent with other
    freelists.  Changes their CompactFreeList apis into ClearFreeList apis and
    calls them via gc.collect().
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  r64845 | raymond.hettinger | 2008-07-10 16:03:19 +0200 (Thu, 10 Jul 2008) | 1 line

  Issue 3301:  Bisect functions behaved badly when lo was negative.
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  r64846 | raymond.hettinger | 2008-07-10 16:34:57 +0200 (Thu, 10 Jul 2008) | 1 line

  Issue 3285: Fractions from_float() and from_decimal() accept Integral arguments.
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  r64849 | andrew.kuchling | 2008-07-10 16:43:31 +0200 (Thu, 10 Jul 2008) | 1 line

  Wording changes
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  r64871 | raymond.hettinger | 2008-07-11 14:00:21 +0200 (Fri, 11 Jul 2008) | 1 line

  Add cautionary note on the use of PySequence_Fast_ITEMS.
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  r64880 | amaury.forgeotdarc | 2008-07-11 23:28:25 +0200 (Fri, 11 Jul 2008) | 5 lines

  #3317 in zipfile module, restore the previous names of global variables:
  some applications relied on them.

  Also remove duplicated lines.
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  r64881 | amaury.forgeotdarc | 2008-07-11 23:45:06 +0200 (Fri, 11 Jul 2008) | 3 lines

  #3342: In tracebacks, printed source lines were not indented since r62555.
  #3343: Py_DisplaySourceLine should be a private function. Rename it to _Py_DisplaySourceLine.
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  r64882 | josiah.carlson | 2008-07-12 00:17:14 +0200 (Sat, 12 Jul 2008) | 2 lines

  Fix for the AttributeError in test_asynchat.
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  r64885 | josiah.carlson | 2008-07-12 01:26:59 +0200 (Sat, 12 Jul 2008) | 2 lines

  Fixed test for asyncore.
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  r64888 | matthias.klose | 2008-07-12 09:51:48 +0200 (Sat, 12 Jul 2008) | 2 lines

  - Fix bashisms in Tools/faqwiz/move-faqwiz.sh
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  r64897 | benjamin.peterson | 2008-07-12 22:16:19 +0200 (Sat, 12 Jul 2008) | 1 line

  fix various doc typos #3320
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  r64900 | alexandre.vassalotti | 2008-07-13 00:06:53 +0200 (Sun, 13 Jul 2008) | 2 lines

  Fixed typo.
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  r64901 | benjamin.peterson | 2008-07-13 01:41:19 +0200 (Sun, 13 Jul 2008) | 1 line

  #1778443 robotparser fixes from Aristotelis Mikropoulos
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  r64915 | nick.coghlan | 2008-07-13 16:52:36 +0200 (Sun, 13 Jul 2008) | 1 line

  Fix issue 3221 by emitting a RuntimeWarning instead of raising SystemError when the parent module can't be found during an absolute import (likely due to non-PEP 361 aware code which sets a module level __package__ attribute)
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  r64926 | martin.v.loewis | 2008-07-13 22:31:49 +0200 (Sun, 13 Jul 2008) | 2 lines

  Add turtle into the module index.
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  r64927 | alexandre.vassalotti | 2008-07-13 22:42:44 +0200 (Sun, 13 Jul 2008) | 3 lines

  Issue #3274: Use a less common identifier for the temporary variable
  in Py_CLEAR().
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  r64928 | andrew.kuchling | 2008-07-13 23:43:25 +0200 (Sun, 13 Jul 2008) | 1 line

  Re-word
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  r64929 | andrew.kuchling | 2008-07-13 23:43:52 +0200 (Sun, 13 Jul 2008) | 1 line

  Add various items; move ctypes items into a subsection of their own
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  r64938 | andrew.kuchling | 2008-07-14 02:35:32 +0200 (Mon, 14 Jul 2008) | 1 line

  Typo fixes
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  r64939 | andrew.kuchling | 2008-07-14 02:40:55 +0200 (Mon, 14 Jul 2008) | 1 line

  Typo fix
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  r64940 | andrew.kuchling | 2008-07-14 03:18:16 +0200 (Mon, 14 Jul 2008) | 1 line

  Typo fix
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  r64941 | andrew.kuchling | 2008-07-14 03:18:31 +0200 (Mon, 14 Jul 2008) | 1 line

  Expand the multiprocessing section
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  r64944 | gregory.p.smith | 2008-07-14 08:06:48 +0200 (Mon, 14 Jul 2008) | 7 lines

  Fix posix.fork1() / os.fork1() to only call PyOS_AfterFork() in the child
  process rather than both parent and child.

  Does anyone actually use fork1()?  It appears to be a Solaris thing
  but if Python is built with pthreads on Solaris, fork1() and fork()
  should be the same.
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  r64961 | jesse.noller | 2008-07-15 15:47:33 +0200 (Tue, 15 Jul 2008) | 1 line

  multiprocessing/connection.py patch to remove fqdn oddness for issue 3270
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  r64966 | nick.coghlan | 2008-07-15 17:40:22 +0200 (Tue, 15 Jul 2008) | 1 line

  Add missing NEWS entry for r64962
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  r64973 | jesse.noller | 2008-07-15 20:29:18 +0200 (Tue, 15 Jul 2008) | 1 line

  Revert 3270 patch: self._address is in pretty widespread use, need to revisit
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2008-07-16 12:55:28 +00:00

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ReStructuredText

:mod:`__future__` --- Future statement definitions
==================================================
.. module:: __future__
:synopsis: Future statement definitions
:mod:`__future__` is a real module, and serves three purposes:
* To avoid confusing existing tools that analyze import statements and expect to
find the modules they're importing.
* To ensure that future_statements run under releases prior to 2.1 at least
yield runtime exceptions (the import of :mod:`__future__` will fail, because
there was no module of that name prior to 2.1).
* To document when incompatible changes were introduced, and when they will be
--- or were --- made mandatory. This is a form of executable documentation, and
can be inspected programmatically via importing :mod:`__future__` and examining
its contents.
Each statement in :file:`__future__.py` is of the form::
FeatureName = _Feature(OptionalRelease, MandatoryRelease,
CompilerFlag)
where, normally, *OptionalRelease* is less than *MandatoryRelease*, and both are
5-tuples of the same form as ``sys.version_info``::
(PY_MAJOR_VERSION, # the 2 in 2.1.0a3; an int
PY_MINOR_VERSION, # the 1; an int
PY_MICRO_VERSION, # the 0; an int
PY_RELEASE_LEVEL, # "alpha", "beta", "candidate" or "final"; string
PY_RELEASE_SERIAL # the 3; an int
)
*OptionalRelease* records the first release in which the feature was accepted.
In the case of a *MandatoryRelease* that has not yet occurred,
*MandatoryRelease* predicts the release in which the feature will become part of
the language.
Else *MandatoryRelease* records when the feature became part of the language; in
releases at or after that, modules no longer need a future statement to use the
feature in question, but may continue to use such imports.
*MandatoryRelease* may also be ``None``, meaning that a planned feature got
dropped.
Instances of class :class:`_Feature` have two corresponding methods,
:meth:`getOptionalRelease` and :meth:`getMandatoryRelease`.
*CompilerFlag* is the (bitfield) flag that should be passed in the fourth
argument to the builtin function :func:`compile` to enable the feature in
dynamically compiled code. This flag is stored in the :attr:`compiler_flag`
attribute on :class:`_Feature` instances.
No feature description will ever be deleted from :mod:`__future__`.