Recursion returning None type? [duplicate]

Question

I wrote a program which finds the super digit of a problem, IE: 9876 = 9+8+7+6 = 30 = 3+0 = super digit = 3 This works fine whenever the program doesn't call on itself, but in the case above, I will get a final integer value of 3, and it will print as such, but when I go to return it, it returns None. Im wondering why this might be the case?

here is the code:

def super_digit(n):
    sup_Digit = 0
    intArray = [int(i) for i in str(n)]
    for i in range(len(intArray)):
        sup_Digit += intArray[i]
    if sup_Digit and sup_Digit < 10:
        return int(sup_Digit)
    else:
        super_digit(sup_Digit)

and here is my test case:

from unittest import TestCase

tc = TestCase()

tc.assertEqual(super_digit(5), 5)
tc.assertEqual(super_digit(30), 3)
tc.assertEqual(super_digit(9876), 3)
tc.assertEqual(super_digit(11111111111111), 5)
tc.assertEqual(super_digit(12345678901234567890), 9)

Answer 1

You forgot the return statement:

def super_digit(n):
    sup_Digit = 0
    intArray = [int(i) for i in str(n)]
    for i in range(len(intArray)):
        sup_Digit += intArray[i]
    if sup_Digit and sup_Digit < 10:
        return int(sup_Digit)
    else:
        return super_digit(sup_Digit)