继承自装饰类 [英] Inheriting from decorated classes

问题描述

我正在尝试用另一个类来装饰一个类。我也想继承装饰类，但是我遇到了一些错误。这是我的代码：

I'm trying to decorate a class with another class. I also want to inherit from the decorated class, but I get some errors. Here's my code:

class Decorator:
    def __init__(self, decorated):
        pass

@Decorator
class Foo:
    pass

class Goo(Foo):
    pass

我尝试从 Foo 进行子类化时得到的错误是：

The error I get when I try to subclass from Foo is this:

回溯（最近一次呼叫最后一次）：

   文件test.py，第9行，在< br>
       class Goo（Foo）：

TypeError：__ init __（）需要2个位置参数（给定4个）

Traceback (most recent call last):
   File "test.py", line 9, in
      class Goo(Foo):
TypeError: __init__() takes exactly 2 positional arguments (4 given)

通过向装饰器添加另一个初始化函数 ...

def __init__(self, *args):
    for arg in args:
        print(arg)

...我得到以下输出：

... I get the following output:

< class'__main __。Foo'>

Goo

（< __ main __。装饰器对象位于0x010073B0>，）< br>
{'__module__'：'_ _ main __'}

<class '__main__.Foo'>
Goo
(<__main__.Decorator object at 0x010073B0>,)
{'__module__': '__main__'}

这些参数是什么以及我应该如何在里面使用它们装饰者？

What are those parameters and how should I be using them inside Decorator?

推荐答案

我会尽力回答什么是那些参数问题。此代码：

I'll try to answer the "what are those parameters" question. This code:

@Decorator
class Foo:
    pass

相当于：

class Foo:
    pass
Foo = Decorator(Foo)

这意味着 Foo 最终成为装饰器类的实例而不是类。

This means that Foo ends up being an instance of the Decorator class instead of being a class.

当您尝试将此实例用作类的基础（ Goo ）时，Python必须确定一个元类，将用于创建新类。在这种情况下，它将使用 Foo .__ class __ 等于装饰器。然后它将使用（name，bases，dict）参数调用元类，并期望它返回一个新类。

When you try to use this instance as a base of a class (Goo), Python will have to determine a metaclass that will be used to create the new class. In this case it will use Foo.__class__ which equals to Decorator. Then it will call the metaclass with (name, bases, dict) arguments and expect it to return a new class.

这是你在装饰器.__ init __ 中结束这些参数的方法。

This is how you end up with these arguments in Decorator.__init__.

关于这一点的更多信息可以找到这里：
http://www.python.org/download/releases/2.2 .3 / descrintro / #metaclasses
（特别是当执行类声明时......部分）

More about this can be found here: http://www.python.org/download/releases/2.2.3/descrintro/#metaclasses (particularly the "When a class statement is executed..." part)

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