code: def get_key_by_job_id(cls, mapreduce_id):
      
      return db.Key.from_path(cls.kind(), "%s:%s" % (mapreduce_id, cls._KEY_NAME))
docs: Retrieves the Key for a mapreduce ID.
  
      Args:
        mapreduce_id: The job to fetch.
  
      Returns:
        Datastore Key for the command for the given job ID.