A simple Python countdown clock.

countdown.py

import sys
from time import sleep

def countdown(seconds):
    while seconds > -1:
        mins, secs = divmod(seconds, 60)
        formatted_time = f"{mins:02d}:{secs:02d}"
        if seconds > 3:
            print(formatted_time, end="\r")
        else:
            print(formatted_time, file=sys.stderr, end="\r") # print final 3 secs in red
        sleep(1)    
        seconds -= 1
    print("Countdown complete!")

user_input = int(input("Enter number of seconds to count down from: "))
countdown(user_input)