code: def lookup_token(self, token):
      if self.unk_index >= 0:
          return self._token2id.get(token, self.unk_index)
      else:
          return self._token2id[token]
  
imports: from typing import Dict
label_desc: Use image node_id 4 for calling the SequenceVocabulary obj's underlying member method code with example usage: obj.lookup_token(token) and returns: self, self