code: def classify(self, token_type, value, lineno, column, line):
          
          if token_type == self.grammar.KEYWORD_TOKEN:
              label_index = self.grammar.keyword_ids.get(value, -1)
              if label_index != -1:
                  return label_index
          label_index = self.grammar.token_ids.get(token_type, -1)
          if label_index == -1:
              raise ParseError("invalid token", token_type, value, lineno, column,
                               line)
          return label_index
docs: Find the label for a token.