定义时如何自动注册一个类 [英] How to auto register a class when it's defined

问题描述

当我定义类时，我想要有一个类注册的实例。理想情况下，下面的代码将会成功。

I want to have an instance of class registered when the class is defined. Ideally the code below would do the trick.

registry = {}

def register( cls ):
   registry[cls.__name__] = cls() #problem here
   return cls

@register
class MyClass( Base ):
   def __init__(self):
      super( MyClass, self ).__init__() 

不幸的是代码生成错误 NameError：全局名称'MyClass'未定义。

Unfortunately, this code generates the error NameError: global name 'MyClass' is not defined.

code> #problem here line我试图实例化一个 MyClass ，但是装饰器还没有返回，所以它不存在

What's going on is at the #problem here line I'm trying to instantiate a MyClass but the decorator hasn't returned yet so it doesn't exist.

这是使用元类或某事吗？

Is the someway around this using metaclasses or something?

推荐答案

p>是的，元类可以做到这一点。元类' __ new __ 方法返回类，所以只需在返回之前注册该类。

Yes, meta classes can do this. A meta class' __new__ method returns the class, so just register that class before returning it.

class MetaClass(type):
    def __new__(cls, clsname, bases, attrs):
        newclass = super(MetaClass, cls).__new__(cls, clsname, bases, attrs)
        register(newclass)  # here is your register function
        return newclass

class MyClass(object):
    __metaclass__ = MetaClass

上一个例子适用于Python 2.x。在Python 3.x中， MyClass 的定义略有不同（而$ code> MetaClass 未显示，因为它不变 - 除了 super（MetaClass，cls）可以成为 super（），如果你想）：

The previous example works in Python 2.x. In Python 3.x, the definition of MyClass is slightly different (while MetaClass is not shown because it is unchanged - except that super(MetaClass, cls) can become super() if you want):

#Python 3.x

class MyClass(metaclass=MetaClass):
    pass

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