In computer programming, the proxy pattern is a software design pattern. A proxy, in its most general form, is a class functioning as an interface to something else. The proxy could interface to anything: a network connection, a large object in memory, a file, or some other resource that is expensive or impossible to duplicate.

def hello():
    print 'hi, i am hello'

def proxy():
    print 'prepare....'
    hello()
    print 'finish....'

if __name__ == '__main__':
    proxy()

prepare....
hi, i am hello
finish....

class AbstractSubject(object):

    def __init__(self):
        pass

    def request(self):
        pass

class RealSubject(AbstractSubject):

    def __init__(self):
        pass
    def request(self):
        print 'hi, i am RealSubject'

class ProxySubject(AbstractSubject):

    def __init__(self):
        self.__rs = RealSubject()

    def request(self):
        self.__beforeRequest()
        self.__rs.request()
        self.__afterRequest()

    def __beforeRequest(self):
        print 'prepare....'

    def __afterRequest(self):
        print 'finish....'

if __name__ == '__main__':
    subject = ProxySubject()
    subject.request()

def __init__(self):
    self.__rs = None

def request(self, *args, **kwargs):
    if self.__rs == None:
        self.__rs = RealSubject(*args, **kwargs)
    self.__beforeRequest()
    self.__rs.request()
    self.__afterRequest()