def tick():
global time1
# get the current local time from the PC
time2 = time.strftime('%H:%M:%S')
# if time string has changed, update it
if time2 != time1:
time1 = time2
clock.config(text=time2)
# calls itself every 200 milliseconds
# to update the time display as needed
# could use >200 ms, but display gets jerky
clock.after(200, tick)