>>> a = [1,2,2,3,1,4,2]
>>> val = 2
>>> [index for index, data in enumerate(a) if data == val ]
[1, 2, 6]

>>> {index : val for index, data in enumerate(a) if data == val }
{1: 2, 2: 2, 6: 2} # index will be unique so we can create it as key