Thumbtack PyCon 2013 challenge

pycon.py

#!/usr/bin/env python

import collections
import itertools
import re
import sys

words = {
    word
    for word in re.split(r'\W+', sys.stdin.read().lower())
    if len(word) >= 4
}
pairs = collections.defaultdict(list)
where = collections.defaultdict(set)
for a, b in itertools.combinations(words, 2):
    key = ''.join(sorted(a + b))
    if key not in where[a] and key not in where[b]:
        pairs[key].append((a, b))
        where[a].add(key)
        where[b].add(key)

max_len = 0
for key in pairs:
    if len(pairs[key]) > max_len:
        max_len = len(pairs[key])

print max_len
for key in pairs:
    if len(pairs[key]) == max_len:
        print pairs[key]