If L1 and L2 are list objects containing keys and respective values, following list comprehension syntax can be used to construct dictionary object.
>>> L1 = ['a','b','c','d']
>>> L2 = [1,2,3,4]
>>> d = {L1[k]:L2[k] for k in range(len(L1))}
>>> d
{'a': 1, 'b': 2, 'c': 3, 'd': 4}