如果不能用定时器中断的话 我不会只能用while实时监测串口接收到的字符吧？

import time
from pyb import Pin, Timer

def tick(timer): # we will receive the timer object when being called
print("Timer callback")
if(uart.any()): print("6")

tim = Timer(4, freq=1) # create a timer object using timer 4 - trigger at 1Hz
tim.callback(tick) # set the callback to our tick function

while (True):
time.sleep(1000)

这个明明没有语法错误 它为什么出错 求大佬解决下