Python OrderedDict

An OrderedDict is a dictionary subclass that remembers the order in which its contents are added


 import collections

print 'Regular dictionary:'
d = {}
d['a'] = 'A'
d['b'] = 'B'
d['c'] = 'C'
d['d'] = 'D'
d['e'] = 'E'

for k, v in d.items():
    print k, v

print '\nOrderedDict:'
d = collections.OrderedDict()
d['a'] = 'A'
d['b'] = 'B'
d['c'] = 'C'
d['d'] = 'D'
d['e'] = 'E'

for k, v in d.items():
    print k, v


 A regular dict does not track the insertion order, and iterating over it produces the values in an arbitrary order. In an OrderedDict, by contrast, the order the items are inserted is remembered and used when creating an iterator.

 A regular dict looks at its contents when testing for equality. An OrderedDict also considers the order the items were added.