Python collections - OrderedDict

OrderDict remembers its insertion order. 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.

All source code available on github

from collections import OrderedDict
d = OrderedDict()

d[3]=5
d[1]=6
d[20]=9
d["cse"]=77

print d

del d[1]
d[1] = 123

print d
print d[1]
print d["cse"]

Output:

OrderedDict([(3, 5), (1, 6), (20, 9), ('cse', 77)])
OrderedDict([(3, 5), (20, 9), ('cse', 77), (1, 123)])
123
77