Python recursive function returning none after completion

Question

My code is supposed to countdown from n to 1. The code completes but returns None at the end. Any suggestions as to why this is happening and how to fix it? Thanks in advance! <

Answer 1

Remove the print(countdown(n)) and replace it with just countdown(n).

What happens is your countdown function returns nothing when n is greater than 0, so that print statement is printing None. You can also remove your else statement in countdown(n) - since you never care about the return value of countdown, it serves no purpose.

def countdown(n):

    '''prints values from n to 1, one per line
    pre: n is an integer > 0
    post: prints values from n to 1, one per line'''

    # Base case is if n is <= 0
    if n > 0:
        print(n)
        countdown(n-1)
    # No need to return a value from here ever - unused in the recursion and
    # you don't mention wanting to have zero printed.
    #else:
    #    return 0

def main():

    # Main function to test countdown
    n = eval(input("Enter n: "))

    # Don't print the result of countdown - just call it
    #print(countdown(n))
    countdown(n)

if __name__ == '__main__':
    main()