python - 如何在类级别正确使用装饰器？

Question

我有一个消息总线，一个类订阅了消息总线的很多方法，例如:

class BookingService(object):
    def start(self):
        self.msg_bus.login(self.user, self.password)
        self.msg_bus.subscribe('/broadcast/aliveResponse', self.handleAliveResponse)
        self.msg_bus.subscribe('/broadcast/musicInfoUpdated', self.handleMusicInfo)
        self.msg_bus.subscribe('/broadcast/radioOnline', self.handleRadioOnline)
        self.msg_bus.subscribe('/broadcast/radioOffline', self.handleRadioOffline)
        self.msg_bus.subscribe('/broadcast/online', self.handleBroadcastOnline)
        self.msg_bus.subscribe('/proxy/aliveResponse', self.handleEvent)
        self.msg_bus.subscribe('/proxy/online', self.handleProxyOnline)
        self.msg_bus.subscribe('/proxy/radioReady', self.handleEvent)
        self.msg_bus.subscribe('/proxy/radioUpdate', self.handleEvent)
        self.msg_bus.subscribe('/proxy/radioClosed', self.handleEvent)
        self.msg_bus.subscribe('/message_bus/detached', self.handleDetached)
        self.msg_bus.run()

它有效，但很难理解每个方法的消息路径是什么，我想要的是使用装饰器来订阅消息总线，它看起来像这样

class BookingService(object):

    @subscribe('/broadcast/aliveResponse')
    @subscribe('/broadcast/onLine')
    def handleEvent(self, dest, data):
        print dest, data

    @subscribe('/proxy/aliveResponse')
    def handleAnotherEvent(self, dest, data):
        print dest, data

但是这里有一些难点要解决，首先msg_bus属性是属于instance的，也就是属于self的。我无法在类里面获得 self.msg_bus。为了解决这个问题，我可以这样写:

class BookingService(object):

    subscribations = []
    def subscribe(dest):
        """Decorator for subscribing function to destination

        """
        def callee(func):
            subscribations.append((dest, func))
            return func
        return callee

    def subscribe_all(self):
        for dest, func in self.subscribations:
            self.msg_bus.subscribe(dest, func)

    @subscribe('/broadcast/aliveResponse')
    def handleEvent(self, dest, data):
        print dest, data

    def start(self):
        self.subscribe_all()

我尝试将订阅收集到 BookingService.subscribations 中，稍后在 subscribe_all 中将它们添加到 msg_bus，但问题来了。我遇到了一个错误

subscribations.append((dest, func))
NameError: global name 'subscribations' is not defined

subscribes好像不在subscribe函数的范围内，请问如何解决？

Answer 1

与其将其放入实例的列表中，不如将其放入函数或类的列表中。

class BookingService(object):

    def subscribe(dest):
        """Decorator for subscribing function to destination

        """
        def callee(func):
            if not hasattr(func, 'subscriptions'):
                func.subscriptions = []
            func.subscriptions.append((dest, func))
            return func
        return callee

    def subscribe_all(self):
        for classmember in dir(self):
            for dest, func in getattr(getattr(self, classmember), 'subscriptions', []):
                self.msg_bus.subscribe(dest, func)

    @subscribe('/broadcast/aliveResponse')
    def handleEvent(self, dest, data):
        print dest, data

    def start(self):
        self.subscribe_all()

然而，您可能仍然遇到未绑定(bind)方法的问题；注意“ self ”的含义。

您可能还想将“subscribe”移到类定义之外，或将其重命名为“_subscribe”，或使其适应被调用为 self.subscribe()(此时 self.subscribe() 会起作用，但不是你期望的那样)