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rephrase dict view docs

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Benjamin Peterson 2008-11-17 21:47:41 +00:00
parent 276c3718e3
commit ce0506ced3
1 changed files with 6 additions and 9 deletions
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15
Doc/library/stdtypes.rst
View File

@ -1881,8 +1881,7 @@ Dictionary view objects
The objects returned by :meth:`dict.keys`, :meth:`dict.values` and
:meth:`dict.items` are *view objects*. They provide a dynamic view on the
dictionary's entries, which means that when the dictionary changes, the view
reflects these changes. The keys and items views have a set-like character
since their entries
reflects these changes.
Dictionary views can be iterated over to yield their respective data, and
support membership tests:
@ -1910,8 +1909,11 @@ support membership tests:
items (in the latter case, *x* should be a ``(key, value)`` tuple).
The keys and items views also provide set-like operations ("other" here refers
to another dictionary view or a set):
Keys views are set-like since their entries are unique and hashable. If all
values are hashable, so that (key, value) pairs are unique and hashable, then
the items view is also set-like. (Values views are not treated as set-like
since the entries are generally not unique.) Then these set operations are
available ("other" refers either to another view or a set):
.. describe:: dictview & other
@ -1931,11 +1933,6 @@ to another dictionary view or a set):
Return the symmetric difference (all elements either in *dictview* or
*other*, but not in both) of the dictview and the other object as a new set.
.. warning::
Since a dictionary's values are not required to be hashable, any of these
four operations will fail if an involved dictionary contains such a value.
An example of dictionary view usage::