ORDERED DICTIONARIES
Regular dictionaries iterate over key/value pairs in arbitrary order. Python 2.7 introduced a new OrderedDict class in the collections module. The OrderedDict API provides the same interface as regular dictionaries but iterates over keys and values in a guaranteed order depending on when a key was first inserted:
>>> from collections import OrderedDict
>>> d = OrderedDict([('first', 1),
...                  ('second', 2),
...                  ('third', 3)])
>>> d.items()
[('first', 1), ('second', 2), ('third', 3)]
If a new entry overwrites an existing entry, the original insertion position is left unchanged:
>>> d['second...
