what is wrong with my Sum of Digits recursive function?

Question

def digital_root(n):
    if n > 0:
        a.append(n%10)
        if n/10 > 0:
            digital_root(n/10)
        else:
            if len(a) > 1:
                b = a
                a.clear()
                z = 0
                for i in range(len(b)):
                    z += b[i]
                digital_root(z)
            else:
                return a[0]

why it returns None?

task is: Given n, take the sum of the digits of n. If that value has more than one digit, continue reducing in this way until a single-digit number is produced. The input will be a non-negative integer.

You need to return the result of the recursive calls. Otherwise, the base-case returns the answer to the previous call, then the result is never propagated past there. — Carcigenicate, Sep 24 '22 at 14:41
Also, not your main question, but note that this: `b = a` makes `b` and `a` the same list (it doesn't make a copy), and then `a.clear()` will wipe that list both variables are looking at. — Carcigenicate, Sep 24 '22 at 14:45

score 0 · Answer 1 · answered Sep 24 '22 at 14:41

0

You got None because you seem to miss return statements when you call digital_root(). Should be:

    return digital_root(n/10)

and

    return digital_root(z)

answered Sep 24 '22 at 14:41

lnstadrum

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what is wrong with my Sum of Digits recursive function?

1 Answers1