code: def UpdateClass(self, class_name, gtfs_class):
      
      if class_name not in self._class_mapping:
        raise problems.NonexistentMapping(class_name)
      self._class_mapping[class_name] = gtfs_class
docs: Updates an entry in the list of known classes.
  
      Args:
          class_name: A string with the class name that is to be updated.
          gtfs_class: The new class
      Raises:
          NonexistentMapping if there is no class with the specified class_name.