How does this countdown timer work?

Question

I've been looking at this for awhile and been going through my head on how it works. I know the first part of it but when I get to the counter I get stuck at

    hr, sc = divmod(counter, 3600)
    mn, sc = divmod(sc, 60)

I've looked into divmod() but I am still confused on what it actually does. And why does sc work here when it isn't defined anywhere else?

To summarize:

1: What is divemod() 2: What does the above code do in the below countdown timer and how does it do it?

hours= int(input("Hours: "))
minutes= int(input("Minutes: "))
sec= int(input("Seconds: "))

counter=hours*3600+minutes*60+sec
mins=int(counter/60)
hr=int(mins/60)

while counter > 0:
    counter-=1
    hr, sc = divmod(counter, 3600)
    mn, sc = divmod(sc, 60)
    print ('%d hours, %d minutes and %d seconds' % (hr, mn, sc))
    mins=int(counter/60)
    hr=int(mins/60)
    time.sleep(1)

Thanks!

Answer 1

Divmod is a function that performs a division and returns two values, the integer quotient and the remainder. It technically returns a two number tuple and that gets unpacked into the two variables.

For example, divmod(10, 3) returns (3, 1) , where 3 is the result of 10 / 3 and 1 is the result of 10 % 3 (10 mod 3).

Saying a, b = divmod(10, 3) is the equivalent of a, b = (3, 1) which assigns 3 to a and 1 to b .

In the case of the timer, this is taking a value of seconds and breaking out the amount of seconds that correspond to quantities of hours and minutes. Every 3600 seconds is an hour and every 60 seconds (after the hours are subtracted) are minutes.

So, when the number of seconds remaining in the timer is 10,000, the first divmod says, "This is actually 2 hours and 2,800 seconds," and the second divmod, performed on 2,800, says, "That is actually 46 minutes and 40 seconds." Put together, these two lines say "10,000 seconds is actually 2 hours, 46 minutes, and 40 seconds."

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Aside 1, the code performing these computations takes non-zero time, so this countdown timer will actually be slower than desired because it takes marginally more than a second to count down each second (it sleeps for a second and then performs some computation).

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Aside 2, the code you wrote could be reduced to the following:

hours = int(input("Hours: "))
minutes = int(input("Minutes: "))
seconds = int(input("Seconds: "))

counter = hours*3600 + minutes*60 + seconds

while counter > 0:
    counter -= 1
    hours, seconds = divmod(counter, 3600)
    minutes, seconds = divmod(seconds, 60)
    print('%d hours, %d minutes and %d seconds' % (hours, minutes, seconds))
    time.sleep(1)

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Aside 3, beware of the input function. If the user types an expression rather than a number, it is evaluated by the python interpreter. See Is it ever useful to use Python's input over raw_input?

You are already casting the results of input to integers. USE raw_input INSTEAD OF input !!!!! (Unless this is python3, in which case raw_input has been renamed input ). For python2, do the following:

hours = int(raw_input("Hours: "))
minutes = int(raw_input("Minutes: "))
seconds = int(raw_input("Seconds: "))