python 把二叉樹打印成多行

'''
題目描述
從上到下按層打印二叉樹，同一層結點從左至右輸出。每一層輸出一行。

思路：
二叉樹的層序遍歷

'''
# -*- coding:utf-8 -*-
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None
class Solution:
    # 返回二維列表[[1,2],[4,5]]
    def Print(self, pRoot):
        # write code here
        if pRoot is None:
            return []
        if pRoot.left is None and pRoot.right is None:
            return [[pRoot.val]]
        stack=[pRoot]
        output=[]
        while(stack):
            temp=[]
            for i in range(len(stack)):
                out_node=stack.pop(0)
                temp.append(out_node.val)
                if out_node.left is not None:
                    stack.append(out_node.left)
                if out_node.right is not None:
                    stack.append(out_node.right)
            output.append(temp)
        return output
if __name__=='__main__':
    here=TreeNode(8)
    here.left=TreeNode(6)
    here.right=TreeNode(10)
    here.left.left=TreeNode(5)
    here.left.right = TreeNode(7)
    here.right.left = TreeNode(9)
    here.right.right = TreeNode(11)
    print(Solution().Print(here))
    #[[8], [6, 10], [5, 7, 9, 11]]