如何实现这个二叉树的访问者模式？

# 二叉树节点类
class TreeNode:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None

    def accept(self, visitor):
        visitor.visit(self)

# 访问者接口
class Visitor:
    def visit(self, node):
        pass

# 具体的访问者类
class PrintVisitor(Visitor):
    def visit(self, node):
        print(node.value)

# 二叉树类
class BinaryTree:
    def __init__(self, root):
        self.root = root

    def traverse(self, visitor):
        self._traverse(self.root, visitor)

    def _traverse(self, node, visitor):
        if node is not None:
            node.accept(visitor)
            self._traverse(node.left, visitor)
            self._traverse(node.right, visitor)

# 创建二叉树
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)

# 创建访问者对象
visitor = PrintVisitor()

# 遍历二叉树并执行访问者操作
tree = BinaryTree(root)
tree.traverse(visitor)