python - RECURSIVE function that will sum digits of input

Question

Trying to write a piece of code that will sum the digits of a number. Also I should add that I want the program to keep summing the digits until the sum is only 1 digit.

For example, if you start with 1969, it should first add 1+9+6+9 to get 25. Since the value 25 has more than a single digit, it should repeat the operation to obtain 7 as a final answer.

Was just wondering how I could pull this off and possibly make it recursive as well. This is what I have so far

def sum_digits3(n):
     r = 0
     while n:
         r, n = r + n % 10, n // 10
     return r   

Answer 1

Convert back and forth between strings and ints, make use of sum().

>>> def foo(n):
    n = str(n)
    if len(n) == 1:
        return int(n)
    return foo(sum(int(c) for c in n))

>>> foo(1969)
7
>>> 

---

def foo(n):
    n = str(n)
    if len(n) == 1:
        return int(n)
    return foo(sum(int(c) for c in n))