from machine import Pin
from time import sleep

led1 = Pin(4, Pin.OUT)
led2 = Pin(0, Pin.OUT)
initial = 1
while True:
    led1.value(initial)
    led2.value(not initial)
    sleep(0.5)
    initial = 0
    led1.value(initial)
    led2.value(not initial)
    sleep(1)
    initial = 1