How to find the indices of common elements in two lists?

E.g. In the following two lists, [3,4] are common in 'a' and 'b'. How to find the indices of [3,4] in lists 'a' and 'b' in pythonic way?

>>> a=[1, 2, 4, 3]

>>> b=[3,4,5,6]

E.g. In the following two lists, [3,4] are common in 'a' and 'b'. How to find the indices of [3,4] in lists 'a' and 'b' in pythonic way?

>>> a=[1, 2, 4, 3]

>>> b=[3,4,5,6]