Python 代理模式讲解和代码示例

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)

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.