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Merged revisions 72572 via svnmerge from 

svn+ssh://pythondev@svn.python.org/python/trunk

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  r72572 | r.david.murray | 2009-05-11 21:36:57 -0400 (Mon, 11 May 2009) | 3 lines

  Make it clear up front that shelve only records changes
  when objects are assigned back to it when writeback is False.
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This commit is contained in:
R. David Murray 2009-05-12 01:40:16 +00:00
parent 4eb88b3baa
commit ff85bcac22
1 changed files with 11 additions and 7 deletions
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18
Doc/library/shelve.rst
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@ -25,13 +25,15 @@ lots of shared sub-objects. The keys are ordinary strings.
By default, version 3 pickles are used to serialize values. The version of the
pickle protocol can be specified with the *protocol* parameter.
By default, mutations to persistent-dictionary mutable entries are not
automatically written back. If the optional *writeback* parameter is set to
*True*, all entries accessed are cached in memory, and written back at close
time; this can make it handier to mutate mutable entries in the persistent
dictionary, but, if many entries are accessed, it can consume vast amounts of
memory for the cache, and it can make the close operation very slow since all
accessed entries are written back (there is no way to determine which accessed
Because of Python semantics, a shelf cannot know when a mutable
persistent-dictionary entry is modified. By default modified objects are
written only when assigned to the shelf (see :ref:`shelve-example`). If
the optional *writeback* parameter is set to *True*, all entries accessed
are cached in memory, and written back at close time; this can make it
handier to mutate mutable entries in the persistent dictionary, but, if
many entries are accessed, it can consume vast amounts of memory for the
cache, and it can make the close operation very slow since all accessed
entries are written back (there is no way to determine which accessed
entries are mutable, nor which ones were actually mutated).
Shelf objects support all methods supported by dictionaries. This eases the
@ -118,6 +120,8 @@ Restrictions
interpretation as for the :class:`Shelf` class.
.. _shelve-example:
Example
-------