Reverse / invert a dictionary mapping

Python 3+:

inv_map = {v: k for k, v in my_map.items()}

Python 2:

inv_map = {v: k for k, v in my_map.iteritems()}

python dictionary mapping reverse

Assuming that the values in the dict are unique:

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

python dictionary mapping reverse

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]

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