这个python“ for”复合语句如何工作？

Question

我看到了a problem on leetcode的以下解决方案：

class Solution:
    def levelOrder(self, root):
        """
        :type root: Node
        :rtype: List[List[int]]
        """

        if root is None:
            return []

        q, res = [root], []
        q1 = []
        while q:
            res.append([node.val for node in q])
            q = [child for node in q for child in node.children]

        return res

[child for node in q for child in node.children]如何工作？将child放在for循环语句之前意味着什么？

Answer 1

这是一个嵌套列表理解。

volume:

等效于：

q = [child for node in q for child in node.children]