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': []}

Answer 2

Try using a slice:

inlinkDict[docid] = adoc[1:]

This will give you an empty list instead of a 0 for the case where only the key value is on the line. To get a 0 instead, use an or (which always returns one of the operands):

inlinkDict[docid] = adoc[1:] or 0

---

Easier way with a dict comprehension:

>>> with open('/tmp/spam.txt') as f:
...     data = [line.split() for line in f]
... 
>>> {d[0]: d[1:] for d in data}
{'A': ['B', 'C', 'D'], 'C': ['A', 'B', 'D'], 'B': ['E', 'F'], 'D': []}
>>> {d[0]: ' '.join(d[1:]) if d[1:] else 0 for d in data}
{'A': 'B C D', 'C': 'A B D', 'B': 'E F', 'D': 0}

Note: dict keys must be unique, so if you have, say, two lines beginning with 'C' the first one will be over-written.

Answer 3

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']