from gpiozero import LED
from time import sleep

red_led = LED(17)
yel_led = LED(23)
grn_led=LED(4)

while True:

    red_led.on()
    sleep(6)

    yel_led.on()
    sleep(2)

    red_led.off()
    yel_led.off()
    grn_led.on()
    sleep(6)

    grn_led.off()
    yel_led.on()
    sleep(2)

    yel_led.off()