python二叉树写法

1. class TreeNode(object):
2. def __init__(self， left=None， right=None， data=None):
3. self.data = data
4. self.left = left
5. self.right = right
6. def preorder(root): #前序遍历
7. if root is None: 
8. return
9. else: 
10. print root.data
11. preorder(root.left)
12. preorder(root.right)
13.
14. def inorder(root): #中序遍历
15. if root is None: 
16.  return
17. else: 
18.  inorder(root.left)
19. print root.data
20. inorder(root.right)
21.
22. def postorder(root): # 后序遍历
23. if root is None: 
24. return 
25. postorder(root.left)
26. postorder(root.right)
27. print root.data