code: def encode(self, s):
      
      sentence = s
      tokens = sentence.strip().split()
      if self._replace_oov is not None:
        tokens = [t if t in self._token_to_id else self._replace_oov
                  for t in tokens]
      ret = [self._token_to_id[tok] for tok in tokens]
      return ret[::-1] if self._reverse else ret
docs: Converts a space-separated string of tokens to a list of ids.