python-树形结构和遍历

#!/usr/bin/python
 
class TreeNode(object):
    def __init__(self,data = 0,left = None,right = None):
        self.data = data
        self.left = left
        self.right = right
 
class Bitree(object):
    def __init__(self,root=None):
        self.root = root
 
    def is_empty(self):
        if self.root is None:
            return True
        else:
            return False
 
    def preOrder(self,treenode):
        if treenode is None:
            return
 
        print(treenode.data)
        self.preOrder(treenode.left)
        self.preOrder(treenode.right)
 
    def inOrder(self,treenode):
 
        if treenode is None:
            return
 
        self.inOrder(treenode.left)
        print(treenode.data)
        self.inOrder(treenode.right)
 
    def postOrder(self,treenode):
 
        if treenode is None:
            return
 
        self.postOrder(treenode.left)
        self.postOrder(treenode.right)
        print(treenode.data)
 
 
 
n1 = TreeNode(1)
n2 = TreeNode(2,n1)
n3 = TreeNode(3)
n4 = TreeNode(4)
n5 = TreeNode(5,n3,n4)
n6 = TreeNode(6,n2,n5)
n7 = TreeNode(7,n6)
n8 = TreeNode(8)
root = TreeNode('root',n7,n8)
 
bt = Bitree(root)
print ('preOrder......')
print (bt.preOrder(bt.root))
print ('inOrder......')
print (bt.inOrder(bt.root))
print ('postOrder.....')
print (bt.postOrder(bt.root))