Simple | Python 3 |  24 ms, faster than 97.61%
\nclass Solution:\n    def reverseStr(self, s: str, k: int) -> str:\n        r = \'\'\n        for i in range(0, len(s), k*2):\n            r += s[i:i+k][::-1] 
```\nclass Solution:\n    def reverseStr(self, s: str, k: int) -> str:\n        r = \'\'\n        for i in range(0, len(s), k*2):\n            r += s[i:i+k][::-1] + s[i+k:i+k+k]\n        return r\n```\nOneliner\n```\nclass Solution:\n    def reverseStr(self, s: str, k: int) -> str:\n        return \'\'.join(s[i:i+k][::-1] + s[i+k:i+k*2] for i in range(0, len(s), k*2))\n```
['Python', 'Python3']