Inverse dictionary lookup in Python

Question

Is there any straightforward way of finding a key by knowing the value within a dictionary?

All I can think of is this:

key = [key for key, value in dict_obj.items() if value == 'value'][0]

Answer 1

Your list comprehension goes through all the dict's items finding all the matches, then just returns the first key. This generator expression will only iterate as far as necessary to return the first value:

key = next(key for key, value in dd.items() if value == 'value')

where dd is the dict. Will raise StopIteration if no match is found, so you might want to catch that and return a more appropriate exception like ValueError or KeyError.