589. N-ary Tree Preorder Traversal - LeetCode

class Node:
    def __init__(self, val=None, children=None):
        self.val = val
        self.children = children


class Solution:
    def preorder(self, root):
        return (
            (root.val,) + sum((self.preorder(x) for x in root.children), ())
            if root
            else ()
        )