Python:复杂的迭代

Question

我见过这段代码，它会迭代类的某些成员(如果存在)。值得注意的是，在二叉树中，迭代子节点直到没有更多的子节点。

二叉树定义为..

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

他们已经这样迭代了:

# type root : TreeNode
def iterateTree(self, root):
    level_list = [root]

    while level_list:

        for item in level_list:
             print(item.val)

        # This iterable seems really complicated for me to understand how they came up with this
        level_list = [child for node in level_list for child in (node.left, node.right) if child]

我不确定他们是如何想出那条线来迭代左右节点的，我不会当场想出这一点...我将如何剖析这条线？

Answer 1

阅读如下:

for node in level_list:
    for child in (node.left, node.right):
        if child:
            child