import machine
import utime
import urandom

led = machine.Pin(25, machine.Pin.OUT)
button = machine.Pin(14, machine.Pin.IN, machine.Pin.PULL_UP)

def button_handler(pin):
    button.irq(handler=None)
    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=machine.Pin.IRQ_RISING, handler=button_handler)