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Merged revisions 72572 via svnmerge from

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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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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 By default, version 3 pickles are used to serialize values. The version of the
pickle protocol can be specified with the *protocol* parameter. pickle protocol can be specified with the *protocol* parameter.
By default, mutations to persistent-dictionary mutable entries are not Because of Python semantics, a shelf cannot know when a mutable
automatically written back. If the optional *writeback* parameter is set to persistent-dictionary entry is modified. By default modified objects are
*True*, all entries accessed are cached in memory, and written back at close written only when assigned to the shelf (see :ref:`shelve-example`). If
time; this can make it handier to mutate mutable entries in the persistent the optional *writeback* parameter is set to *True*, all entries accessed
dictionary, but, if many entries are accessed, it can consume vast amounts of are cached in memory, and written back at close time; this can make it
memory for the cache, and it can make the close operation very slow since all handier to mutate mutable entries in the persistent dictionary, but, if
accessed entries are written back (there is no way to determine which accessed 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). entries are mutable, nor which ones were actually mutated).
Shelf objects support all methods supported by dictionaries. This eases the Shelf objects support all methods supported by dictionaries. This eases the
@ -118,6 +120,8 @@ Restrictions
interpretation as for the :class:`Shelf` class. interpretation as for the :class:`Shelf` class.
.. _shelve-example:
Example Example
------- -------