Anagrams using MapReduce and mrjob

This code discovers anagrams. The input is a text file dictionary with one word per line. The output is a text file.  

#! /usr/bin/env python

from mrjob.job import MRJob

class Anagram(MRJob):
 def mapper(self, _, word):
  letters = list(word)
  letters.sort()
  if word != '':
   yield letters, word

 def reducer(self, _, words):
  anagrams = [w for w in words]
  if len(anagrams) >= 2:
   yield len(anagrams), anagrams

if __name__ == '__main__':
 Anagram.run()

Call it like this:

Sample output:

The output file consists of two columns: the first column is the number of word in the set, and the second column is the set itself.