【编程思想】【设计模式】【行为模式Behavioral】访问者模式Visitor

最新推荐文章于 2025-03-05 13:31:24 发布

转载最新推荐文章于 2025-03-05 13:31:24 发布 · 56 阅读

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原文链接：http://www.cnblogs.com/demonzk/p/9035681.html

本文通过Python代码示例介绍了一种设计模式——访客模式。该模式将算法从对象结构中分离出来，允许为对象结构定义新的操作而无需修改对象结构本身。文中详细解释了如何实现这一设计模式，并提供了具体的运行输出。

Python版

https://github.com/faif/python-patterns/blob/master/behavioral/visitor.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
http://peter-hoffmann.com/2010/extrinsic-visitor-pattern-python-inheritance.html

*TL;DR80
Separates an algorithm from an object structure on which it operates.
"""


class Node(object):
    pass


class A(Node):
    pass


class B(Node):
    pass


class C(A, B):
    pass


class Visitor(object):

    def visit(self, node, *args, **kwargs):
        meth = None
        for cls in node.__class__.__mro__:
            meth_name = 'visit_' + cls.__name__
            meth = getattr(self, meth_name, None)
            if meth:
                break

        if not meth:
            meth = self.generic_visit
        return meth(node, *args, **kwargs)

    def generic_visit(self, node, *args, **kwargs):
        print('generic_visit ' + node.__class__.__name__)

    def visit_B(self, node, *args, **kwargs):
        print('visit_B ' + node.__class__.__name__)


a = A()
b = B()
c = C()
visitor = Visitor()
visitor.visit(a)
visitor.visit(b)
visitor.visit(c)

### OUTPUT ###
# generic_visit A
# visit_B B
# visit_B C