from machine import Pin, Timer

led = Pin(2, Pin.OUT)
tim = Timer(0)


def ctr_led_handler(led_pin):
    led_pin.value(not led_pin.value())


tim.init(period=500, mode=Timer.PERIODIC,
         callback=lambda t: ctr_led_handler(led))

# tim.init(period=500, mode=Timer.PERIODIC,
#          callback=lambda t: led.value(not led.value()))