Question

What is the ‘most pythonic’ way to build a dictionary where I have the values in a sequence and each key will be a function of its value? I’m currently using the following, but I feel like I’m just missing a cleaner way. NOTE: values is a list that is not related to any dictionary.

for value in values:     new_dict[key_from_value(value)] = value 

Answer 1

>>> l = [ 1, 2, 3, 4 ] >>> dict( ( v, v**2 ) for v in l ) {1: 1, 2: 4, 3: 9, 4: 16} 

In Python 3.0 you can use a ‘dict comprehension’ which is basically a shorthand for the above:

{ v : v**2 for v in l }