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

The accepted answer is correct, except that it reads the entire file into memory (may not be desirable if you have a large file), and it will overwrite duplicate keys.

An alternate approach using defaultdict, which is available from Python 2.4 solves this:

from collections import defaultdict
d = defaultdict(list)
with open('/tmp/spam.txt') as f:
  for line in f:
    parts = line.strip().split()
    d[parts[0]] += parts[1:]

Input:

A B C D
B E F
C A B D
D  
C H I J

Result:

>>> d = defaultdict(list)
>>> with open('/tmp/spam.txt') as f:
...    for line in f:
...      parts = line.strip().split()
...      d[parts[0]] += parts[1:]
...
>>> d['C']
['A', 'B', 'D', 'H', 'I', 'J']