how to set countdown timer in python tkinter code example

Example: python countdown timer tkinter

import time
from tkinter import *
from tkinter import messagebox


f = ("Arial",24)

ws = Tk()
ws.geometry("300x250+1500+700")
ws.title("PythonGuides")
ws.config(bg='#345')

hour=StringVar()
minute=StringVar()
second=StringVar()

hour.set("00")
minute.set("00")
second.set("10")

hour_tf= Entry(
	ws, 
	width=3, 
	font=f,
	textvariable=hour
	)

hour_tf.place(x=80,y=20)

mins_tf= Entry(
	ws, 
	width=3, 
	font=f,
	textvariable=minute)

mins_tf.place(x=130,y=20)

sec_tf = Entry(
	ws, 
	width=3, 
	font=f,
	textvariable=second)

sec_tf.place(x=180,y=20)


def startCountdown():
	try:
		userinput = int(hour.get())*3600 + int(minute.get())*60 + int(second.get())
	except:
		messagebox.showwarning('', 'Invalid Input!')
	while userinput >-1:
		mins,secs = divmod(userinput,60) 

		hours=0
		if mins >60:
			
		
			hours, mins = divmod(mins, 60)
	
		hour.set("{0:2d}".format(hours))
		minute.set("{0:2d}".format(mins))
		second.set("{0:2d}".format(secs))

	
		ws.update()
		time.sleep(1)

	
		if (userinput == 0):
			messagebox.showinfo("", "Time's Up")
		

		userinput -= 1

start_btn = Button(
	ws, 
	text='START', 
	bd='5',
	command= startCountdown
	)

start_btn.place(x = 120,y = 120)


ws.mainloop()