输入一个数字，求每一位相加之和

题目描述：

# In this kata, you must create a digital root function.
#
# A digital root is the recursive sum of all the digits in a number. 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. 
This is only applicable to the natural numbers.


我的解答：

def sum_digits(n):
    if n < 10:
        return n
    else:
        return sum_digits(n // 10) + sum_digits(n % 10)

def digital_root(n):
    if n < 10:
        return n
    else:
        n = (n // 10) + (n % 10)
        return digital_root(n)

def sum_digits(n):
    if n < 10:
        return n
    else:
        return sum_digits(sum(map(int, str(n))))