dictionary - 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.)