from machine import Pin
import utime
import urandom

pressed = False
led = Pin(21, Pin.OUT)
button = Pin(4, Pin.IN, Pin.PULL_DOWN)

def button_handler(pin):
    global pressed
    if not pressed:
        pressed = True
        timer_reaction = utime.ticks_diff(utime.ticks_ms(), timer_start)
        print("Your reaction time was " + str(timer_reaction) + " milliseconds!")

led.value(1)
utime.sleep(urandom.uniform(5, 10))
led.value(0)
timer_start = utime.ticks_ms()
button.irq(trigger=Pin.IRQ_RISING, handler=button_handler)