Function is returning 'None' while computing the 'Additive Persistence' of a Number

Question

Have this print statement which correctly calculates the value of 'Count' and that is what I am returning, but eventually I am getting 'None' as a result. Please point out the correction that have to make the function provide the correct value of count...

def additive_persistence(num, count):
    sumer = 0
    num_copy = num

    while num_copy:
        sumer = sumer + (num_copy % 10)
        num_copy = num_copy // 10
    count += 1
    print(sumer, count)      # just to check the calculation is right!
    if sumer > 9:
        num = sumer
        additive_persistence(num, count)

    else:    
        return (count)

counter = 0    
number = int(input("Enter Number: "))
add_pers = additive_persistence(number, counter)
print("Additive Persistence of number {}, is: {}".format(number, add_pers))

Because you are not _returning_ the result here: `additive_persistence(num, count)` — mshsayem, Oct 21 '17 at 09:57
I take it you're using recursion here because it's part of an assignment because it's a lot simpler not doing so :) — Jon Clements, Oct 21 '17 at 10:02
@Adarsh just saying that recursion isn't necessary and not the easiest of ways to actually solve this - it'd be far more readable, understandable and less error-prone written iteratively... — Jon Clements, Oct 21 '17 at 10:08
Thanks for your input @JonClements, will try to rewrite the code without using recursion :) — Adarsh Namdev, Oct 21 '17 at 10:12

score 3 · Answer 1 · answered Oct 21 '17 at 09:57

3

You have failed to recurse properly.

  return additive_persistence(num, count)

answered Oct 21 '17 at 09:57

Ignacio Vazquez-Abrams

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score 0 · Accepted Answer · answered Oct 21 '17 at 09:58

0

You need to call your function and return its value in a recursive function:

   while num_copy:
        sumer = sumer + (num_copy % 10)
        num_copy = num_copy // 10
    count += 1
    print(sumer, count)      # just to check the calculation is right!
    if sumer > 9:
        num = sumer
        return additive_persistence(num, count)

answered Oct 21 '17 at 09:58

Chen A.

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3
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Thanks for correcting the code.. its working now! I understood the fact that I should be returning some value too when I am calling the function again inside it! – Adarsh Namdev Oct 21 '17 at 10:10
Yep, that's how it works. This is called recursive function, since you call the same function from inside of it. – Chen A. Oct 21 '17 at 10:11

Function is returning 'None' while computing the 'Additive Persistence' of a Number

2 Answers2