在子类中如何装饰继承的方法？ [英] How would one decorate an inherited method in the child class?

问题描述

我不太确定如何在继承的方法上使用装饰器。装饰器通常放在定义之前，但对于继承的函数，定义是在父类而不是子类中给出的。我想避免在子类中重写方法的定义，而只需指定将装饰器放在继承的方法周围。

I'm not quite sure how to use a decorator on an inherited method. Normally decorators are put before the definition but for an inherited function the definition is given in the parent and not the child class. I would like to avoid rewriting the definition of the method in the child class and simply specify to put the decorator around the inherited method.

为了使自己更清楚，这是一个我的意思的工作示例：

To make myself clearer, here is a working example of what I mean:

class Person():
    def __init__(self, age):
        self.age = age

    @classmethod
    def gets_drink(cls, ):
        print "it's time to get a drink!"
        return "A beer"

def dec(some_f):
    def legal_issue(obj,):
        some_f(obj)
        return 'A Coke'
    return legal_issue

class Child(Person):
    def __init__(self, age):
        Person.__init__(self, age=age)

    #in principle i'd like to write
    #@dec
    #self.gets_drink
    #which does not work
    #the only working way I found is by defining the method as a classmethod
    #and write this:

    @dec
    def gets_drink(self, ):
        return Person.gets_drink()

dad = Person(42)
son = Child(12)

print dad.gets_drink()
print son.gets_drink()

此示例中的工作方式有效，但对我来说看起来有点怪异，用调用方法代替了原始方法只能将装饰器放进去。同样，要使此方法起作用，需要将该方法定义为父类中的类方法。

The way it is done in this example works, but it looks somehow weird to me, replacing the method with a call to the original method only to be able to put the decorator. Also, for this to work, the method needs to be defined as a classmethod in the parent class.

我错过了什么吗？有经验的开发人员将如何做到这一点？

Am I missing something? How would experienced developers do this?

任何帮助，见解，评论和免费咖啡都将受到赞赏！

Any help, insights, critical comments and free coffees are much appreciated!

推荐答案

您没有必须在装饰器语法中使用装饰器。这只是可调用的：

You don't have to use a decorator in decorator syntax. It is just a callable:

class Child(Person):
    def __init__(self, age):
        Person.__init__(self, age=age)

    gets_drink = dec(Person.gets_drink.__func__)

这会将装饰器的返回值作为具有相同名称的方法添加到子类中。 __ func __ 属性解开绑定（类）方法，检索原始函数。

This adds the return value of the decorator to the child class as a method with the same name. The __func__ attribute unwraps the bound (class) method, retrieving the original function.

请注意，您的新方法是现在是常规方法，而不是类方法，则必须在 classmethod（）调用中重新包装结果。

Note that your new method is now a regular method, not a classmethod, you'd have to re-wrap the result in a classmethod() call for that.

之所以有效是因为语法

@decorator_expression
def function_definition():
    pass

仅仅是以下方面的语法糖：

is just syntactic sugar for:

def function_definition():
    pass
function_definition = decorator_expression(function_definition)

这篇关于在子类中如何装饰继承的方法？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！