像这样的，只能进行到l3.off,后面的代码也会print("------",a)但是打印的不是接收到的

import time,pyb
from pyb import UART
l1 = pyb.LED(1)
l3 = pyb.LED(3)
uart = UART(3,9600,timeout_char=1000)
while True:
    l3.on()
    if uart.any():
        l3.off()
        l1.on()
        a = []
        a = uart.readline()
        print(":-----",a)
        l1.off()
        time.sleep(500)