Create Countdown Timer using Python-Tkinter

Prerequisites: Python GUI – tkinter
Python Tkinter is a GUI programming package or built-in library. Tkinter provides the Tk GUI toolkit with a potent object-oriented interface. Python with Tkinter is the fastest and easiest way to create GUI applications. Creating a GUI using Tkinter is an easy task.
Approach

1. Importing the module – tkinter, time
2. Create the main window (container)
3. Add number of widgets to the main window:Button, Entry
4. Apply the event Trigger on the widgets.

Below is the implementation. 

python3

import time
from tkinter import *
from tkinter import messagebox


# creating Tk window
root = Tk()

# setting geometry of tk window
root.geometry("300x250")

# Using title() to display a message in
# the dialogue box of the message in the
# title bar.
root.title("Time Counter")

# Declaration of variables
hour=StringVar()
minute=StringVar()
second=StringVar()

# setting the default value as 0
hour.set("00")
minute.set("00")
second.set("00")

# Use of Entry class to take input from the user
hourEntry= Entry(root, width=3, font=("Arial",18,""),
                 textvariable=hour)
hourEntry.place(x=80,y=20)

minuteEntry= Entry(root, width=3, font=("Arial",18,""),
                   textvariable=minute)
minuteEntry.place(x=130,y=20)

secondEntry= Entry(root, width=3, font=("Arial",18,""),
                   textvariable=second)
secondEntry.place(x=180,y=20)


def submit():
    try:
        # the input provided by the user is
        # stored in here :temp
        temp = int(hour.get())*3600 + int(minute.get())*60 + int(second.get())
    except:
        print("Please input the right value")
    while temp >-1:

        # divmod(firstvalue = temp//60, secondvalue = temp%60)
        mins,secs = divmod(temp,60)

        # Converting the input entered in mins or secs to hours,
        # mins ,secs(input = 110 min --> 120*60 = 6600 => 1hr :
        # 50min: 0sec)
        hours=0
        if mins >60:

            # divmod(firstvalue = temp//60, secondvalue
            # = temp%60)
            hours, mins = divmod(mins, 60)

        # using format () method to store the value up to
        # two decimal places
        hour.set("{0:2d}".format(hours))
        minute.set("{0:2d}".format(mins))
        second.set("{0:2d}".format(secs))

        # updating the GUI window after decrementing the
        # temp value every time
        root.update()
        time.sleep(1)

        # when temp value = 0; then a messagebox pop's up
        # with a message:"Time's up"
        if (temp == 0):
            messagebox.showinfo("Time Countdown", "Time's up ")

        # after every one sec the value of temp will be decremented
        # by one
        temp -= 1

# button widget
btn = Button(root, text='Set Time Countdown', bd='5',
             command= submit)
btn.place(x = 70,y = 120)

# infinite loop which is required to
# run tkinter program infinitely
# until an interrupt occurs
root.mainloop()

Output: