Converts a list of subtoken to a list of tokens.

        Args:
          subtokens: a list of integers in the range [0, vocab_size)

        Returns:
          a list of strings.

def _subtoken_to_tokens(self, subtokens):
        """ Converts a list of subtoken to a list of tokens.

        Args:
          subtokens: a list of integers in the range [0, vocab_size)

        Returns:
          a list of strings.
        """
        concatenated = "".join(subtokens)
        split = concatenated.split("_")
        return [_unescape_token(t + "_") for t in split if t]