使用示例：尽管代理模式在绝大多数 Python 程序中并不常见， 但它在一些特殊情况下仍然非常方便。 当你希望在无需修改客户代码的前提下于已有类的对象上增加额外行为时， 该模式是无可替代的。
识别方法：代理模式会将所有实际工作委派给一些其他对象。 除非代理是某个服务的子类， 否则每个代理方法最后都应该引用一个服务对象。
概念示例
本例说明了代理设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
main.py: 概念示例
from abc import ABC, abstractmethodclass Subject(ABC): """ The Subject interface declares common operations for both RealSubject and the Proxy. As long as the client works with RealSubject using this interface, you'll be able to pass it a proxy instead of a real subject. """ @abstractmethod def request(self) -> None: passclass RealSubject(Subject): """ The RealSubject contains some core business logic. Usually, RealSubjects are capable of doing some useful work which may also be very slow or sensitive - e.g. correcting input data. A Proxy can solve these issues without any changes to the RealSubject's code. """ def request(self) -> None: print("RealSubject: Handling request.")class Proxy(Subject): """ The Proxy has an interface identical to the RealSubject. """ def __init__(self, real_subject: RealSubject) -> None: self._real_subject = real_subject def request(self) -> None: """ The most common applications of the Proxy pattern are lazy loading, caching, controlling the access, logging, etc. A Proxy can perform one of these things and then, depending on the result, pass the execution to the same method in a linked RealSubject object. """ if self.check_access(): self._real_subject.request() self.log_access() def check_access(self) -> bool: print("Proxy: Checking access prior to firing a real request.") return True def log_access(self) -> None: print("Proxy: Logging the time of request.", end="")def client_code(subject: Subject) -> None: """ The client code is supposed to work with all objects (both subjects and proxies) via the Subject interface in order to support both real subjects and proxies. In real life, however, clients mostly work with their real subjects directly. In this case, to implement the pattern more easily, you can extend your proxy from the real subject's class. """ # ... subject.request() # ...if __name__ == "__main__": print("Client: Executing the client code with a real subject:") real_subject = RealSubject() client_code(real_subject) print("") print("Client: Executing the same client code with a proxy:") proxy = Proxy(real_subject) client_code(proxy)
Output.txt: 执行结果
Client: Executing the client code with a real subject: RealSubject: Handling request. Client: Executing the same client code with a proxy: Proxy: Checking access prior to firing a real request. RealSubject: Handling request. Proxy: Logging the time of request.
