from machine import Pin 
import time 
led1= Pin(0, Pin.OUT)
led2= Pin(1, Pin.OUT)
led3= Pin(2, Pin.OUT)
while True:
    led1.value(1)
    led2.value(0)
    led3.value(0)
    time.sleep(3) # wait for USB to become ready
    led1.value(0)
    led2.value(1)
    led3.value(0)
    time.sleep(3)
    led1.value(0)
    led2.value(0)
    led3.value(1)
    time.sleep(3)