code: def ngrams(self, n=3):
      
      if n <= 0:
          return []
      grams = [WordList(self.words[i:i+n], parent=self)
                          for i in range(len(self.words) - n + 1)]
      return grams
docs: Return a list of n-grams (tuples of n successive words) for this
      blob.
      :rtype: List of :class:`WordLists <WordList>`