'Train the Chunker on the ConLL-2000 corpus.'

@requires_nltk_corpus
def train(self):

    train_data = [[(t, c) for (_, t, c) in nltk.chunk.tree2conlltags(sent)] for sent in nltk.corpus.conll2000.chunked_sents(u'train.txt', chunk_types=[u'NP'])]
    unigram_tagger = nltk.UnigramTagger(train_data)
    self.tagger = nltk.BigramTagger(train_data, backoff=unigram_tagger)
    self._trained = True
