collections.OrderedDict

An OrderedDict is a data type in the collections module. It is a dict subclass that tracks the order in which items were added. It offers all the standard dictionary methods as well as two additional methods that deal with the ordering of the OrderedDict.

myOrderedDict = collections.OrderedDict()

Like a regular dictionary, an OrderedDict can also be initialized with the .fromkeys() method.

myOrderedDict = collections.OrderedDict.fromkeys(keylist, value)

In addition to the standard dict methods, the following are specific to an OrderedDict:

• .popitem(last): Returns and removes a key-value pair from the OrderedDict. The pairs are returned in LIFO (last-in-first-out) order if last is True and FIFO (first-in-first-out) order if last is False. The last argument is optional and defaults to True.
• .move_to_end(key, last): Moves the key to one end of the OrderedDict. If last is True it is moved to the right end (last entered). Otherwise, it is moved to the start (first entered). The last argument is optional and defaults to True.

The following example creates an OrderedDict and rearranges some items in it.

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