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

def init(self,root):

self.root = root
# 判空
def is_empty(self):
    if self.root is None:
        return True
    return False

#  先序遍历
def pre_order(self,tree_node):
    print tree_node.data
    if tree_node.left is not None:
        self.pre_order(tree_node.left)
    if tree_node.right is not None:
        self.pre_order(tree_node.right)

# 中序遍历
def in_order(self,tree_node):

    if tree_node.left is not None:
        self.in_order(tree_node.left)
    print tree_node.data
    if tree_node.right is not None:
        self.in_order(tree_node.right)

# 后序遍历
def post_order(self,tree_node):
    if tree_node.left is not None:
        self.post_order(tree_node.left)
    if tree_node.right is not None:
        self.post_order(tree_node.right)
    print tree_node.data
tree_d = TreeNode(left=None,right=None,data='D')

tree_e = TreeNode(left=None,data='E')

tree_f = TreeNode(left=None,data='F')

tree_b = TreeNode(left=tree_d,right=tree_e,data='B')

tree_c = TreeNode(left=tree_f,data='C')

tree_a = TreeNode(left=tree_b,right=tree_c,data='A')

下面是测试代码

btree = BTree(tree_a)
print btree.is_empty()
btree.pre_order(btree.root)
btree.in_order(btree.root)
btree.post_order(btree.root)