<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def encode(self, s):
 """Converts a space-separated string of tokens to a list of ids."""

    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