Python 3 (30ms) | Perfect Pythonic Recursive One-Liner | Easy to Understand
\nclass Solution:\n    def preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:\n        if root is None:\n            return []\n        return [roo
```\nclass Solution:\n    def preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:\n        if root is None:\n            return []\n        return [root.val] + self.preorderTraversal(root.left) + self.preorderTraversal(root.right)\n\n```
['Recursion', 'Binary Tree', 'Python', 'Python3']