get keys correspond to a value in dictionary

Question

I have this dictionary in python

d={1: 'a', 2: 'b', 3: 'c'}

with d[1] I get

>>> d[1]
'a'

how I can get the key correspond to a value ?
example : with 'a' get 1

Answer 1

You want to invert the mapping:

As shown in this question

dict((v,k) for k, v in map.iteritems())

Answer 2

You could create a new dictionary from the keys and values in the initial one:

>>> d2 = dict((v, k) for k, v in d.iteritems())
>>> d2
{'a': 1, 'c': 3, 'b': 2}
>>> d2['a']
1