How to initialize a dict with keys from a list and empty value in Python?

Question

I'd like to get from this:

keys = [1,2,3] 

to this:

{1: None, 2: None, 3: None} 

Is there a pythonic way of doing it?

This is an ugly way to do it:

>>> keys = [1,2,3] >>> dict([(1,2)]) {1: 2} >>> dict(zip(keys, [None]*len(keys))) {1: None, 2: None, 3: None} 

Answer 1

dict.fromkeys([1, 2, 3, 4])

This is actually a classmethod, so it works for dict-subclasses (like collections.defaultdict) as well. The optional second argument specifies the value to use for the keys (defaults to None.)

Answer 2

nobody cared to give a dict-comprehension solution ?

>>> keys = [1,2,3,5,6,7] >>> {key: None for key in keys} {1: None, 2: None, 3: None, 5: None, 6: None, 7: None}