b.py

#!/usr/bin/python
def cut(lst):
  return lst[:5]

with open("words") as f:
  all_words = f.read().split("\n")

common = filter(lambda word: all(c.islower() for c in word), all_words)
fours = filter(lambda s: len(s)==4, common)

from collections import defaultdict

def msk(mask, word):
  return ''.join('_' if m == '1' else c for c, m in zip(word, mask))

masks = ['']
for i in range(4):
  masks = map(lambda w: w + '0', masks) + map(lambda w: w + '1', masks)

clues = defaultdict(list)
for word in fours:
  for mask in masks:
    clue = msk(mask, word)
    clues[clue].append(word)

a, b = clues['n___'], clues['_n__']
print cut(a), len(a)
print cut(b), len(b)

clues = list(clues.iteritems())
clues.sort(key=lambda (clue,lst): len(lst), reverse=True)
for clue,lst in cut(clues):
  print clue, cut(lst), len(lst)
#update