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

print(countdown(n)) prints the value returned by countdown(n). If n > 0, the returned value is None, since Python functions return None by default if there is no return statement executed.

Since you are printing values inside countdown, the easiest way to fix the code is to simply remove the print call in main():

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)

def main():

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

if __name__ == '__main__':
    main()

Edit: Removed the else-clause since the docstring says the last value printed is 1, not 0.