timer.py

#Import the required library
from tkinter import *
import time
#Create an instance of tkinter frame
win = Tk()
win.geometry('750x300')
win.resizable(False,False)
#Configure the background
win.config(bg='burlywood1')
#Create Entry Widgets for HH MM SS
sec = StringVar()
Entry(win, textvariable=sec, width = 2, font = 'Helvetica 14').place(x=220, y=120)
sec.set('00')
mins= StringVar()
Entry(win, textvariable = mins, width =2, font = 'Helvetica 14').place(x=180, y=120)
mins.set('00')
hrs= StringVar()
Entry(win, textvariable = hrs, width =2, font = 'Helvetica 14').place(x=142, y=120)
hrs.set('00')
#Define the function for the timer
def countdowntimer():
   times = int(hrs.get())*3600+ int(mins.get())*60 + int(sec.get())
   while times > -1:
      minute,second = (times // 60 , times % 60)
      hour =0
      if minute > 60:
         hour , minute = (minute // 60 , minute % 60)
      sec.set(second)
      mins.set(minute)
      hrs.set(hour)
      #Update the time
      win.update()
      time.sleep(1)
      if(times == 0):
         sec.set('00')
         mins.set('00')
         hrs.set('00')
      times -= 1
Label(win, font =('Helvetica bold',22), text = 'Set the Timer',bg='burlywood1').place(x=105,y=70)
Button(win, text='START', bd ='2', bg = 'IndianRed1',font =('Helvetica bold',10), command = countdowntimer).place(x=167, y=165)
win.mainloop()