Return Value of None?

Question

I’m trying to solve a problem on CodeWars with the following specifications:

“Write a function, persistence, that takes in a positive parameter num and returns its multiplicative persistence, which is the number of times you must multiply the digits in num until you reach a single digit.”

My solution is as follows:

def persistence(n,count = 0):
    n = list(str(n))
    if len(n)  <= 1 :
        count = 0
        return count
    else :
        num_per = 1
        for i in n :
            num_per = num_per * int(i)
        num_dump = num_per
        if len(str(num_dump)) > 1:
            count += 1
            n = num_per
            persistence(n,count)
        else:
            count = count + 1
            return count

When I choose any number with more than a single digit, I get a return value of ‘None’. I’ve narrowed down the problem to the last return statement in the second else clause. The number of counts are calculated correctly,but the return statement still returns a value of ‘None’. Any help would be greatly appreciated.

Asked By: M.Spillers

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Source

Answer 1

Just add return before your persistence line:

return persistence(n, count)

Answered By: Akaisteph7

Answer 2

Going off of what @jasonharper suggested, your function has an if/else statement which is decided by len(n) <= 1. If the length of n is less than 1, count (which is 0) is returned.

In your else statement however, you have another if/else statement. In your if statement, which is decided by len(str(num_dump)) > 1, you decide to recursively call the same function, however, you return no value. Therefore, your program most likely makes a lot of recursive calls but has no way of storing the values to be returned at the end of the program.

This can be fixed by replacing

persistence(n, count)

with

return persistence(n, count)

Answered By: NolanRudolph

Return Value of None?

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