code: def tgt_vocab(self):
          
          if self._tgt_vocab is None:
              tgt_vocab_file_name, tgt_vocab_hash = \
                  self._data_file[self._pair_key]['vocab' + '_' + self._tgt_lang]
              [tgt_vocab_path] = self._fetch_data_path([(tgt_vocab_file_name, tgt_vocab_hash)])
              with io.open(tgt_vocab_path, 'r', encoding='utf-8') as in_file:
                  self._tgt_vocab = Vocab.from_json(in_file.read())
          return self._tgt_vocab
docs: Target Vocabulary of the Dataset.
  
          Returns
          -------
          tgt_vocab : Vocab
              Target vocabulary.