给定一个非负整数num,重复的加每一位，直到最后只剩一位

gistfile1.txt

def add(*args):
    from functools import reduce
    sum = reduce(lambda x,y:x+y, args)
    return sum

def sum(fn, num):
    while True:
        if num < 9:
            return num
        
        num = fn(*[int(i) for i in str(num)])

sum(add, 102)