from machine import Pin,Timer
import utime
# leds=[]
# for i in range (3):
#     leds.append(Pin(i+1,Pin.OUT))
# cnt=0
# for led in leds:
#     led.value(0)
# def fn(timer):
#     for led in leds:
#         led.value(0)
#     global cnt
#     leds[cnt].value(1)
#     cnt=(cnt+1)%3
# t = Timer(period=1000,mode=Timer.PERIODIC,callback=fn)
leds=[]
for i in range (3):
    leds.append(Pin(i+1,Pin.OUT))
cnt=0
delay=1.5
for led in leds:
    led.value(0)
def fn(timer):
    for led in leds:
        led.value(0)
    global cnt
    if cnt==0:
        if delay==0.5:
            delay=1.5
        else:
            delay=0.5
    leds[cnt].value(1)
    utime.sleep(delay)
    cnt=(cnt+1)%3
t = Timer(period=1,mode=Timer.PERIODIC,callback=fn)