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PEP 372: OrderedDict()

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Raymond Hettinger 2009-03-02 21:24:57 +00:00
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Doc/library/collections.rst
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@ -14,7 +14,7 @@
__name__ = '<doctest>'
This module implements high-performance container datatypes. Currently,
there are three datatypes, :class:`Counter`, :class:`deque` and
there are four datatypes, :class:`Counter`, :class:`deque`, :class:`OrderedDict` and
:class:`defaultdict`, and one datatype factory function, :func:`namedtuple`.
The specialized containers provided in this module provide alternatives
@ -806,6 +806,33 @@ and more efficient to use a simple class declaration:
adapted for Python 2.4.
:class:`OrderedDict` objects
----------------------------
Ordered dictionaries are just like regular dictionaries but they remember the
order that items were inserted. When iterating over an ordered dictionary,
the items are returned in the order their keys were first added.
.. class:: OrderedDict([items])
Return an instance of a dict subclass, supporting the usual :class:`dict`
methods. An *OrderedDict* is a dict that remembers the order that keys
were first inserted. If a new entry overwrites an existing entry, the
original insertion position is left unchanged. Deleting an entry and
reinserting it will move it to the end.
.. versionadded:: 2.7
The :meth:`popitem` method for ordered dictionaries returns and removes the
last added entry. The key/value pairs are returned in LIFO order.
Equality tests between :class:`OrderedDict` objects are order-sensitive
and are implemented as ``list(od1.items())==list(od2.items())``.
Equality tests between :class:`OrderedDict` objects and other
:class:`Mapping` objects are order-insensitive like regular dictionaries.
This allows :class:`OrderedDict` objects to be substituted anywhere a
regular dictionary is used.
:class:`UserDict` objects
-------------------------