Simple CPS counter

[GalaxyCoyote]

I am trying to make a CPS counter, you will press a button and the timer starts then it will record your CPS and display it at the end of the second.

My trouble is the timer, time.sleep() doesn't work as that would stop everything, so I need a simple timer.

Here is the code so far.

import turtle
cps = 0 #is the CPS goes up when seconddone = False and sets to 0 when seconddone = True
seconddone = True #tells when the timer starts 
wn = turtle.Screen()
wn.setup(width=200, height=200)
wn.bgcolor("white")

cpsb = turtle.Turtle()
cpsb.shape("square")
cpsb.color("black")
cpsb.goto(0,0)

def start():
    seconddone = False
def click():
    cps = cps + 1

wn.onscreenclick(click, 1)
wn.onscreenclick(start, 3)
wn.onkeypress()
wn.listen()
while True:
    wn.update()
while seconddone:
    cps = 0

if anyone could help with making a timer that would be great (note I dont want to optimize the code at this point)