这段二叉排序树的创建代码，二叉排序树,代码出自《Program

这段二叉排序树的创建代码，二叉排序树,代码出自《Program

代码出自《Programming Python》4th Edition

class BinaryTree:    def __init__(self):        self.tree = EmptyNode()    def __repr__(self):        return repr(self.tree)    def lookup(self, value):        return self.tree.lookup(value)    def insert(self, value):        self.tree = self.tree.insert(value)class EmptyNode:    def __repr__(self):        return '*'    def lookup(self, value):                      # fail at the bottom        return False    def insert(self, value):        return BinaryNode(self, value, self)      # add new node at bottomclass BinaryNode:    def __init__(self, left, value, right):        self.data, self.left, self.right  =  value, left, right    def lookup(self, value):        if self.data == value:            return True        elif self.data > value:            return self.left.lookup(value)               # look in left        else:            return self.right.lookup(value)              # look in right    def insert(self, value):        if self.data > value:            self.left = self.left.insert(value)          # grow in left        elif self.data < value:            self.right = self.right.insert(value)        # grow in right        return self    def __repr__(self):        return ('( %s, %s, %s )' %                 (repr(self.left), repr(self.data), repr(self.right)))>>>bt = BinaryTree()>>>for i in [3, 1, 9, 2, 7]:>>>    bt.insert(i)>>> bt( ( *, 1, ( *, 2, * ) ), 3, ( ( *, 7, * ), 9, * ) )#该片段来自于http://byrx.net