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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def tgt_vocab(self):
 """Target Vocabulary of the Dataset. Returns ------- tgt_vocab : Vocab Target vocabulary. """

        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