python時戳轉換成字符串日期，並形成時間序列文件

#########  Get all performance data of one object
def get_one_object_perfor_data(object_id,dst_dir,src_file_name):
    df = pd.read_csv(src_file_name,delimiter=',',header=0)
    df_tmp1 = df[df['res_ins_id'] == object_id]
    i=0
    df_tmp=df_tmp1.reset_index(drop=True)##index need to be reset from 0 to N
    for time_id in df_tmp['time_id']:
        d_time = dt.datetime.fromtimestamp(time_id/1000)
        #df_tmp['time_id'][i] = d_time.strftime("%Y-%m-%d %H:%M:%S.%f")
        df_tmp['time_id'][i] = d_time.strftime("%Y-%m-%d")
        i=i+1
    df_tmp.to_csv(path_or_buf=os.path.join(dst_dir,str(object_id)+'.csv'))
    return 0