python 控制电源模块for循环写法

   for i in range(20):
        challenge_pin = get_challenge_pin(url)
        if challenge_pin is not None:
            pin = challenge_pin + "test" + challenge_pin
        try:
            password = my_js_md5(s=pin)
            get_login_cookie(url,password)
        except:
            print("get challenge pin failed ,please rerun !")
            continue
        else:   # try当不报错 -> else
            # 90s后关机
            print('starting to shutdown PC after 90s!')
            rst = runCommand(cmd)
            # 关机
            time.sleep(30)
            turn_on_off(3,'off')