caculate total response time of all meta_datas

def __get_total_response_time(meta_datas_expanded):
    """ caculate total response time of all meta_datas
    """
    try:
        response_time = 0
        for meta_data in meta_datas_expanded:
            response_time += meta_data["stat"]["response_time_ms"]

        return "{:.2f}".format(response_time)

    except TypeError:
        # failure exists
        return "N/A"