Reverse / invert a dictionary mapping

Question

Given a dictionary like so:

my_map = {\'a\': 1, \'b\': 2}

How can one invert this map to get:

inv_map = {1: \'a\', 2: \'b\'         


        

Answer 1

If the values in my_map aren't unique:

inv_map = {}
for k, v in my_map.iteritems():
    inv_map[v] = inv_map.get(v, []) + [k]