Python：可以在构建类型时调用

Python：可以在构建类型时调用__subclasses __（），而不是自定义对象(Python: can call __subclasses__() on build in types, not on custom object) class Test: pass print(Test.__subclasses__())

收益：

AttributeError: class Test has no attribute '__subclasses__'

和

print(int.__subclasses__())

收益：

[<type 'bool'>]

为什么我不能在自定义对象上调用子类 （）？

这种构建方法不适用于自定义类型，是吗？

每个类都保留一个对其直接子类的弱引用列表。 该方法返回所有这些仍然存在的引用的列表。 例：

class Test: pass print(Test.__subclasses__())

returns:

AttributeError: class Test has no attribute '__subclasses__'

And

print(int.__subclasses__())

returns:

[<type 'bool'>]

Why can't I call subclasses() on my custom object?

This build in methods aren't reserver for custom types, are they?

Each class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. Example:

最满意答案

你需要这样做： -

class Foo(object): pass # This works perfectly fine now. print(Foo.__subclasses__())

上面的类是一个“新风格”的类，因为它继承了对象类。 新式类提供了许多“旧式”类没有的额外框架。 新样式类的一个特定属性是能够使用子类方法确定类的子类 。

You will need to do this:-

class Foo(object): pass # This works perfectly fine now. print(Foo.__subclasses__())

The class above is a "new-style" class because it inherits from the object class. New-style classes provide a lot of extra framework that "old-style" classes do not have. One particular attribute of a new-style class is to be able to determine the subclasses of the class with the subclasses method.