def get_robots_sn(robots_list):
    """
    Get the sn for the robots_list,
    :param robots_list: which robots need to get sn
    :return: robots_sn_dict = {sn:robot_obj, ...}
    """
    robots_sn_dict = {}
    for robot_obj in robots_list:
        sn = robot_obj.get_sn()
        robots_sn_dict[sn] = robot_obj
    return robots_sn_dict