Python 自定义二叉树结构

class BinaryTree:
    def __init__(self,value):
        self._left=None
        self._right=None
        self._data=value
 
    def insertLeftChild(self,value):        #创建左子树
        if self._left:
            print('left child tree already exists.')
        else:
            self._left=BinaryTree(value)
            return self._left
 
    def insertRightChild(self,value):          #创建右子树
        if self._right:
            print('right child tree already exists.')
        else:
            self._right=BinaryTree(value)
            return self._right
 
    def show(self):
        print(self._data)
 
    def preOrder(self):       #前序遍历（根左右）
        print(self._data)
        if self._left:
            self._left.preOrder()
        if self._right:
            self._right.preOrder()
 
    def postOrder(self):               #后序遍历（左右根）
        if self._left:
            self._left.postOrder()
        if self._right:
            self._right.postOrder()
        print(self._data)
 
    def inOrder(self):             #中序遍历（左根右）
        if self._left:
            self._left.inOrder()
        print(self._data)
        if self._right:
            self._right.inOrder()
 
if __name__=='__main__':
    print('Please use me as a module.')