在Python中删除二叉树节点。为什么是self != parent.left还是parent.right？

class TreeNode:
    def __init__(self, val=0, left=None, right=None, parent=None):
        self.val = val
        self.left = left
        self.right = right
        self.parent = parent

def delete_node(node):
    parent = node.parent

    if parent is None:
        # 如果要删除的节点是根节点，则直接将根节点置为None
        node = None
    elif node == parent.left:
        # 如果要删除的节点是父节点的左子节点
        parent.left = None
    elif node == parent.right:
        # 如果要删除的节点是父节点的右子节点
        parent.right = None

    # 其他删除操作，例如释放节点内存等

# 示例用法
root = TreeNode(1)
left_child = TreeNode(2, parent=root)
right_child = TreeNode(3, parent=root)
root.left = left_child
root.right = right_child

delete_node(left_child)