python二叉树遍历的实现方法

#!/usr/bin/python
# -*- coding: utf-8 -*-

class TreeNode(object):
    def __init__(self,data=0,left=0,right=0):
        self.data = data
        self.left = left
        self.right = right

class BTree(object):
    def __init__(self,root=0):
        self.root = root

    def is_empty(self):
        if self.root is 0:
            return True
        else:
            return False

    def preOrder(self,treenode):
        if treenode is 0:
            return
        print treenode.data
        self.preOrder(treenode.left)
        self.preOrder(treenode.right)

    def inOrder(self,treenode):
        if treenode is 0:
            return
        self.inOrder(treenode.left)
        print treenode.data
        self.inOrder(treenode.right)

    def postOrder(self,treenode):
        if treenode is 0:
            return
        self.postOrder(treenode.left)
        self.postOrder(treenode.right)
        print treenode.data

n1 = TreeNode(data=1)
n2 = TreeNode(2,n1,0)
n3 = TreeNode(3)
n4 = TreeNode(4)
n5 = TreeNode(5,n3,n4)
n6 = TreeNode(6,n2,n5)
n7 = TreeNode(7,n6,0)
n8 = TreeNode(8)
root = TreeNode('root',n7,n8)

bt = BTree(root)
print 'preOrder......'
print bt.preOrder(bt.root)
print 'inOrder......'
print bt.inOrder(bt.root)
print 'postOrder.....'
print bt.postOrder(bt.root)