code: def evaluate(self, gold):
          
          tagged_sents = self.tag_sents([w for (w, t) in sent] for sent in gold)
          gold_tokens = sum(gold, [])
          test_tokens = sum(tagged_sents, [])
          accuracy = float(sum(x == y for x, y in six.moves.zip(gold_tokens, test_tokens))) / len(test_tokens)
          return accuracy
docs: Evaluate the accuracy of this tagger using a gold standard corpus.
  
          :param list(list(tuple(str, str))) gold: The list of tagged sentences to score the tagger on.
          :returns: Tagger accuracy value.
          :rtype: float