from machine import Pin
import time
 
ledr = Pin(23, Pin.OUT)
ledy = Pin(22, Pin.OUT)
ledg = Pin(21, Pin.OUT)

Leds = [ledr, ledy, ledg]

for led in Leds:
    led.value(0)

delays = [2,0.5,1]

while True:
    for i in range(3):
        led_on  = Leds[i]
        led_off = Leds[i-1]
        led_on.value(1)
        led_off.value(0)
        time.sleep(delays[i])