'Score the accuracy of the tagger against the gold standard.
Strip the tags from the gold standard text, retag it using
the tagger, then compute the accuracy score.
:type gold: list(list(tuple(str, str)))
:param gold: The list of tagged sentences to score the tagger on.
:rtype: float'

def evaluate(self, gold):

    tagged_sents = self.tag_sents((untag(sent) for sent in gold))
    gold_tokens = list(chain(*gold))
    test_tokens = list(chain(*tagged_sents))
    return accuracy(gold_tokens, test_tokens)
