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| -rw-r--r-- | Doc/library/collections.rst | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst index 48cac2f6c9..88c4f0f9ee 100644 --- a/Doc/library/collections.rst +++ b/Doc/library/collections.rst @@ -818,6 +818,9 @@ semantics pass-in keyword arguments using a regular unordered dictionary. `Equivalent OrderedDict recipe <http://code.activestate.com/recipes/576693/>`_ that runs on Python 2.4 or later. +:class:`OrderedDict` Examples and Recipes +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + Since an ordered dictionary remembers its insertion order, it can be used in conjuction with sorting to make a sorted dictionary:: @@ -846,12 +849,29 @@ If a new entry overwrites an existing entry, the original insertion position is changed and moved to the end:: class LastUpdatedOrderedDict(OrderedDict): + 'Store items in the order the keys were last added' def __setitem__(self, key, value): if key in self: del self[key] OrderedDict.__setitem__(self, key, value) +An ordered dictionary can combined with the :class:`Counter` class +so that the counter remembers the order elements are first encountered:: + + class OrderedCounter(Counter, OrderedDict): + 'Counter that remembers the order elements are first encountered' + + def __init__(self, iterable=None, **kwds): + OrderedDict.__init__(self) + Counter.__init__(self, iterable, **kwds) + + def __repr__(self): + return '%s(%r)' % (self.__class__.__name__, OrderedDict(self)) + + def __reduce__(self): + return self.__class__, (OrderedDict(self),) + .. _abstract-base-classes: |