将类属性反向映射到Python中的类 [英] Reverse mapping class attributes to classes in Python

问题描述

我在Python中有一些代码，其中将有一堆类，每个类都有一个属性_internal_attribute.我希望能够生成这些属性到原始类的映射.本质上，我希望能够做到这一点:

I have some code in Python where I'll have a bunch of classes, each of which will have an attribute _internal_attribute. I would like to be able to generate a mapping of those attributes to the original class. Essentially I would like to be able to do this:

class A(object):
    _internal_attribute = 'A attribute'
class B(object):
    _internal_attribute = 'B attribute'

a_instance = magic_reverse_mapping['A attribute']()
b_instance = magic_reverse_mapping['B attribute']()

我在这里缺少的是如何生成magic_reverse_mapping字典.我有一种直觉，认为让一个元类生成A和B是解决此问题的正确方法.看起来正确吗?

What I'm missing here is how to generate magic_reverse_mapping dict. I have a gut feeling that having a metaclass generate A and B is the correct way to go about this; does that seem right?

推荐答案

您可以使用元类在magic_reverse_mapping中自动注册您的类:

You can use a meta class to automatically register your classes in magic_reverse_mapping:

magic_reverse_mapping = {}

class MagicRegister(type):
   def __new__(meta, name, bases, dict):
      cls = type.__new__(meta, name, bases, dict)
      magic_reverse_mapping[dict['_internal_attribute']] = cls
      return cls

class A(object):
    __metaclass__ = MagicRegister
    _internal_attribute = 'A attribute'

afoo = magic_reverse_mapping['A attribute']()

或者，您可以在类上使用装饰器进行注册.我认为这更具可读性，更容易理解:

Alternatively you can use a decorator on your classes to register them. I think this is more readable and easier to understand:

magic_reverse_mapping = {}

def magic_register(cls):
   magic_reverse_mapping[cls._internal_attribute] = cls
   return cls

@magic_register
class A(object):
    _internal_attribute = 'A attribute'

afoo = magic_reverse_mapping['A attribute']()

或者您甚至可以手工完成.不使用任何魔法就没那么多工作了:

Or you could even do it by hand. It's not that much more work without using any magic:

reverse_mapping = {}

class A(object):
    _internal_attribute = 'A attribute'

reverse_mapping[A._internal_attribute] = A

看看不同的变体，我认为装饰器版本将是最令人愉悦的.

Looking at the different variants I think the decorator version would be the most pleasant to use.

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