summaryrefslogtreecommitdiff
path: root/Doc/library/weakref.rst
diff options
context:
space:
mode:
authorChristian Heimes <christian@cheimes.de>2008-03-23 21:54:12 +0000
committerChristian Heimes <christian@cheimes.de>2008-03-23 21:54:12 +0000
commitfe337bfd0d89c62917e3625111c65f4aa187c6b4 (patch)
tree5b2b30e195ce4e9b43fc6defe9482fb9f6eabd21 /Doc/library/weakref.rst
parentfae759fb276b9e17fe09ecf37ecce618bc9bbb58 (diff)
downloadcpython-git-fe337bfd0d89c62917e3625111c65f4aa187c6b4.tar.gz
Merged revisions 61724-61725,61731-61735,61737,61739,61741,61743-61744,61753,61761,61765-61767,61769,61773,61776-61778,61780-61783,61788,61793,61796,61807,61813 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk ................ r61724 | martin.v.loewis | 2008-03-22 01:01:12 +0100 (Sat, 22 Mar 2008) | 49 lines Merged revisions 61602-61723 via svnmerge from svn+ssh://pythondev@svn.python.org/sandbox/trunk/2to3/lib2to3 ........ r61626 | david.wolever | 2008-03-19 17:19:16 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Added fixer for implicit local imports. See #2414. ........ r61628 | david.wolever | 2008-03-19 17:57:43 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Added a class for tests which should not run if a particular import is found. ........ r61629 | collin.winter | 2008-03-19 17:58:19 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Two more relative import fixes in pgen2. ........ r61635 | david.wolever | 2008-03-19 20:16:03 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Fixed print fixer so it will do the Right Thing when it encounters __future__.print_function. 2to3 gets upset, though, so the tests have been commented out. ........ r61637 | david.wolever | 2008-03-19 21:37:17 +0100 (Mi, 19 M?\195?\164r 2008) | 3 lines Added a fixer for itertools imports (from itertools import imap, ifilterfalse --> from itertools import filterfalse) ........ r61645 | david.wolever | 2008-03-19 23:22:35 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line SVN is happier when you add the files you create... -_-' ........ r61654 | david.wolever | 2008-03-20 01:09:56 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Added an explicit sort order to fixers -- fixes problems like #2427 ........ r61664 | david.wolever | 2008-03-20 04:32:40 +0100 (Do, 20 M?\195?\164r 2008) | 3 lines Fixes #2428 -- comments are no longer eatten by __future__ fixer. ........ r61673 | david.wolever | 2008-03-20 17:22:40 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Added 2to3 node pretty-printer ........ r61679 | david.wolever | 2008-03-20 20:50:42 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Made node printing a little bit prettier ........ r61723 | martin.v.loewis | 2008-03-22 00:59:27 +0100 (Sa, 22 M?\195?\164r 2008) | 2 lines Fix whitespace. ........ ................ r61725 | martin.v.loewis | 2008-03-22 01:02:41 +0100 (Sat, 22 Mar 2008) | 2 lines Install lib2to3. ................ r61731 | facundo.batista | 2008-03-22 03:45:37 +0100 (Sat, 22 Mar 2008) | 4 lines Small fix that complicated the test actually when that test failed. ................ r61732 | alexandre.vassalotti | 2008-03-22 05:08:44 +0100 (Sat, 22 Mar 2008) | 2 lines Added warning for the removal of 'hotshot' in Py3k. ................ r61733 | georg.brandl | 2008-03-22 11:07:29 +0100 (Sat, 22 Mar 2008) | 4 lines #1918: document that weak references *to* an object are cleared before the object's __del__ is called, to ensure that the weak reference callback (if any) finds the object healthy. ................ r61734 | georg.brandl | 2008-03-22 11:56:23 +0100 (Sat, 22 Mar 2008) | 2 lines Activate the Sphinx doctest extension and convert howto/functional to use it. ................ r61735 | georg.brandl | 2008-03-22 11:58:38 +0100 (Sat, 22 Mar 2008) | 2 lines Allow giving source names on the cmdline. ................ r61737 | georg.brandl | 2008-03-22 12:00:48 +0100 (Sat, 22 Mar 2008) | 2 lines Fixup this HOWTO's doctest blocks so that they can be run with sphinx' doctest builder. ................ r61739 | georg.brandl | 2008-03-22 12:47:10 +0100 (Sat, 22 Mar 2008) | 2 lines Test decimal.rst doctests as far as possible with sphinx doctest. ................ r61741 | georg.brandl | 2008-03-22 13:04:26 +0100 (Sat, 22 Mar 2008) | 2 lines Make doctests in re docs usable with sphinx' doctest. ................ r61743 | georg.brandl | 2008-03-22 13:59:37 +0100 (Sat, 22 Mar 2008) | 2 lines Make more doctests in pprint docs testable. ................ r61744 | georg.brandl | 2008-03-22 14:07:06 +0100 (Sat, 22 Mar 2008) | 2 lines No need to specify explicit "doctest_block" anymore. ................ r61753 | georg.brandl | 2008-03-22 21:08:43 +0100 (Sat, 22 Mar 2008) | 2 lines Fix-up syntax problems. ................ r61761 | georg.brandl | 2008-03-22 22:06:20 +0100 (Sat, 22 Mar 2008) | 4 lines Make collections' doctests executable. (The <BLANKLINE>s will be stripped from presentation output.) ................ r61765 | georg.brandl | 2008-03-22 22:21:57 +0100 (Sat, 22 Mar 2008) | 2 lines Test doctests in datetime docs. ................ r61766 | georg.brandl | 2008-03-22 22:26:44 +0100 (Sat, 22 Mar 2008) | 2 lines Test doctests in operator docs. ................ r61767 | georg.brandl | 2008-03-22 22:38:33 +0100 (Sat, 22 Mar 2008) | 2 lines Enable doctests in functions.rst. Already found two errors :) ................ r61769 | georg.brandl | 2008-03-22 23:04:10 +0100 (Sat, 22 Mar 2008) | 3 lines Enable doctest running for several other documents. We have now over 640 doctests that are run with "make doctest". ................ r61773 | raymond.hettinger | 2008-03-23 01:55:46 +0100 (Sun, 23 Mar 2008) | 1 line Simplify demo code. ................ r61776 | neal.norwitz | 2008-03-23 04:43:33 +0100 (Sun, 23 Mar 2008) | 7 lines Try to make this test a little more robust and not fail with: timeout (10.0025) is more than 2 seconds more than expected (0.001) I'm assuming this problem is caused by DNS lookup. This change does a DNS lookup of the hostname before trying to connect, so the time is not included. ................ r61777 | neal.norwitz | 2008-03-23 05:08:30 +0100 (Sun, 23 Mar 2008) | 1 line Speed up the test by avoiding socket timeouts. ................ r61778 | neal.norwitz | 2008-03-23 05:43:09 +0100 (Sun, 23 Mar 2008) | 1 line Skip the epoll test if epoll() does not work ................ r61780 | neal.norwitz | 2008-03-23 06:47:20 +0100 (Sun, 23 Mar 2008) | 1 line Suppress failure (to avoid a flaky test) if we cannot connect to svn.python.org ................ r61781 | neal.norwitz | 2008-03-23 07:13:25 +0100 (Sun, 23 Mar 2008) | 4 lines Move itertools before future_builtins since the latter depends on the former. From a clean build importing future_builtins would fail since itertools wasn't built yet. ................ r61782 | neal.norwitz | 2008-03-23 07:16:04 +0100 (Sun, 23 Mar 2008) | 1 line Try to prevent the alarm going off early in tearDown ................ r61783 | neal.norwitz | 2008-03-23 07:19:57 +0100 (Sun, 23 Mar 2008) | 4 lines Remove compiler warnings (on Alpha at least) about using chars as array subscripts. Using chars are dangerous b/c they are signed on some platforms and unsigned on others. ................ r61788 | georg.brandl | 2008-03-23 09:05:30 +0100 (Sun, 23 Mar 2008) | 2 lines Make the doctests presentation-friendlier. ................ r61793 | amaury.forgeotdarc | 2008-03-23 10:55:29 +0100 (Sun, 23 Mar 2008) | 4 lines #1477: ur'\U0010FFFF' raised in narrow unicode builds. Corrected the raw-unicode-escape codec to use UTF-16 surrogates in this case, just like the unicode-escape codec. ................ r61796 | raymond.hettinger | 2008-03-23 14:32:32 +0100 (Sun, 23 Mar 2008) | 1 line Issue 1681432: Add triangular distribution the random module. ................ r61807 | raymond.hettinger | 2008-03-23 20:37:53 +0100 (Sun, 23 Mar 2008) | 4 lines Adopt Nick's suggestion for useful default arguments. Clean-up floating point issues by adding true division and float constants. ................ r61813 | gregory.p.smith | 2008-03-23 22:04:43 +0100 (Sun, 23 Mar 2008) | 6 lines Fix gzip to deal with CRC's being signed values in Python 2.x properly and to read 32bit values as unsigned to start with rather than applying signedness fixups allover the place afterwards. This hopefully fixes the test_tarfile failure on the alpha/tru64 buildbot. ................
Diffstat (limited to 'Doc/library/weakref.rst')
-rw-r--r--Doc/library/weakref.rst44
1 files changed, 26 insertions, 18 deletions
diff --git a/Doc/library/weakref.rst b/Doc/library/weakref.rst
index 83e6000de4..bffa2ba9e6 100644
--- a/Doc/library/weakref.rst
+++ b/Doc/library/weakref.rst
@@ -24,18 +24,20 @@ only remaining references to a referent are weak references,
:term:`garbage collection` is free to destroy the referent and reuse its memory
for something else. A primary use for weak references is to implement caches or
mappings holding large objects, where it's desired that a large object not be
-kept alive solely because it appears in a cache or mapping. For example, if you
-have a number of large binary image objects, you may wish to associate a name
-with each. If you used a Python dictionary to map names to images, or images to
-names, the image objects would remain alive just because they appeared as values
-or keys in the dictionaries. The :class:`WeakKeyDictionary` and
-:class:`WeakValueDictionary` classes supplied by the :mod:`weakref` module are
-an alternative, using weak references to construct mappings that don't keep
-objects alive solely because they appear in the mapping objects. If, for
-example, an image object is a value in a :class:`WeakValueDictionary`, then when
-the last remaining references to that image object are the weak references held
-by weak mappings, garbage collection can reclaim the object, and its
-corresponding entries in weak mappings are simply deleted.
+kept alive solely because it appears in a cache or mapping.
+
+For example, if you have a number of large binary image objects, you may wish to
+associate a name with each. If you used a Python dictionary to map names to
+images, or images to names, the image objects would remain alive just because
+they appeared as values or keys in the dictionaries. The
+:class:`WeakKeyDictionary` and :class:`WeakValueDictionary` classes supplied by
+the :mod:`weakref` module are an alternative, using weak references to construct
+mappings that don't keep objects alive solely because they appear in the mapping
+objects. If, for example, an image object is a value in a
+:class:`WeakValueDictionary`, then when the last remaining references to that
+image object are the weak references held by weak mappings, garbage collection
+can reclaim the object, and its corresponding entries in weak mappings are
+simply deleted.
:class:`WeakKeyDictionary` and :class:`WeakValueDictionary` use weak references
in their implementation, setting up callback functions on the weak references
@@ -49,6 +51,12 @@ they need -- it's not usually necessary to create your own weak references
directly. The low-level machinery used by the weak dictionary implementations
is exposed by the :mod:`weakref` module for the benefit of advanced uses.
+.. note::
+
+ Weak references to an object are cleared before the object's :meth:`__del__`
+ is called, to ensure that the weak reference callback (if any) finds the
+ object still alive.
+
Not all objects can be weakly referenced; those objects which can include class
instances, functions written in Python (but not in C), instance methods, sets,
frozensets, file objects, :term:`generator`\s, type objects, :class:`DBcursor`
@@ -130,11 +138,11 @@ Extension types can easily be made to support weak references; see
.. note::
- Caution: Because a :class:`WeakKeyDictionary` is built on top of a Python
+ Caution: Because a :class:`WeakKeyDictionary` is built on top of a Python
dictionary, it must not change size when iterating over it. This can be
- difficult to ensure for a :class:`WeakKeyDictionary` because actions performed
- by the program during iteration may cause items in the dictionary to vanish "by
- magic" (as a side effect of garbage collection).
+ difficult to ensure for a :class:`WeakKeyDictionary` because actions
+ performed by the program during iteration may cause items in the
+ dictionary to vanish "by magic" (as a side effect of garbage collection).
:class:`WeakKeyDictionary` objects have the following additional methods. These
expose the internal references directly. The references are not guaranteed to
@@ -229,7 +237,7 @@ Weak Reference Objects
----------------------
Weak reference objects have no attributes or methods, but do allow the referent
-to be obtained, if it still exists, by calling it::
+to be obtained, if it still exists, by calling it:
>>> import weakref
>>> class Object:
@@ -242,7 +250,7 @@ to be obtained, if it still exists, by calling it::
True
If the referent no longer exists, calling the reference object returns
-:const:`None`::
+:const:`None`:
>>> del o, o2
>>> print(r())