code: def stem(self, words):
          
          stemmer = PorterStemmer()
          _stem = stemmer.stem
          for word in words:
              yield _stem(word, 0, len(word) - 1)
docs: Use the porter stemmer to generate consistent forms of
          words, e.g.::
  
              from walrus.search.utils import PorterStemmer
              stemmer = PorterStemmer()
              for word in ['faith', 'faiths', 'faithful']:
                  print s.stem(word, 0, len(word) - 1)
  
              # Prints:
              # faith
              # faith
              # faith