Creating a dictionary with list of lists in Python

Question

I have a huge file (with around 200k inputs). The inputs are in the form:

A B C D
B E F
C A B D
D  

I am reading this file and storing it i

Answer 1

A dictionary comprehension makes short work of this task:

>>> s = [['A','B','C','D'], ['B','E','F'], ['C','A','B','D'], ['D']]
>>> {t[0]:t[1:] for t in s}
{'A': ['B', 'C', 'D'], 'C': ['A', 'B', 'D'], 'B': ['E', 'F'], 'D': []}