Simple Python Solution
\nclass Solution:\n    def digitSum(self, s: str, k: int) -> str:\n        while len(s) > k:\n            strList = [s[i:i+k] for i in range(0, len(s), k)]\n   
```\nclass Solution:\n    def digitSum(self, s: str, k: int) -> str:\n        while len(s) > k:\n            strList = [s[i:i+k] for i in range(0, len(s), k)]\n            \n            for idx, _s in enumerate(strList):\n                strList[idx] = self.getSum(_s)\n            s = "".join(strList)\n        return s\n    \n    def getSum(self, s: str) -> str:\n        return str(sum(map(int, list(s))))\n```
['Python']