在装饰器类内部，访问包含装饰方法的类的实例 [英] Inside a decorator-class, access instance of the class which contains the decorated method

问题描述

我有以下装饰器，该装饰器在用 @saveconfig 装饰的方法被调用后保存配置文件：

I have the following decorator, which saves a configuration file after a method decorated with @saveconfig is called:

class saveconfig(object):
    def __init__(self, f):
        self.f = f

    def __call__(self, *args):
        self.f(object, *args)
        # Here i want to access "cfg" defined in pbtools
        print "Saving configuration"

我在下面的类中使用此装饰器。调用方法 createkvm 之后，配置对象 self.cfg 应该保存在装饰器中：

I'm using this decorator inside the following class. After the method createkvm is called, the configuration object self.cfg should be saved inside the decorator:

class pbtools()
    def __init__(self):
        self.configfile = open("pbt.properties", 'r+')
        # This variable should be available inside my decorator
        self.cfg = ConfigObj(infile = self.configfile)

    @saveconfig
    def createkvm(self):
        print "creating kvm"

我的问题是我需要访问装饰器 saveconfig 中的对象变量 self.cfg 。第一种幼稚的方法是向装饰器添加一个参数，该装饰器保存对象，例如 @saveconfig（self），但这是行不通的。

My problem is that i need to access the object variable self.cfg inside the decorator saveconfig. A first naive approach was to add a parameter to the decorator which holds the object, like @saveconfig(self), but this doesn't work.

如何访问装饰器内部方法主机的对象变量？我是否必须在同一类中定义装饰器才能访问？

How can I access object variables of the method host inside the decorator? Do i have to define the decorator inside the same class to get access?

推荐答案

您必须让装饰器类表现为描述符以能够访问实例：

You have to make your decorator class behave as a descriptor to be able to access the instance:

class saveconfig(object):
    def __init__(self, f):
        self.f = f

    def __get__(self, instance, owner):
        def wrapper(*args):
            print "Saving configuration"
            print instance.cfg
            return self.f(instance, *args)
        return wrapper

您的代码将对象作为第一个参数传递给 self.f （），它应应该传递 pbtools 实例。

Your code passes object as first parameter to self.f(), where it should pass the pbtools instance.

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