New to coding. Here is my naive recursive approach:

```
class Solution(object):
def addDigits(self, num):
"""
:type num: int
:rtype: int
"""
sum=0
while num>=10:
sum+=num%10
num=num//10
sum+=num
if sum<10:
return sum
else:
return self.addDigits(sum)
```

Comments are welcome!