__subclassess __（）函数不存在

Question

我想获取班级中的班级列表。根据这个答案How to find all the subclasses of a class given its name?，我应该可以使用cls.__subclasses__，但是此功能不存在。

我尝试了问题How to find all the subclasses of a class given its name?

的答案

class X:
  class my_subclass:
    pass

x=X()
x.__subclassess__()

# This reports AttributeError 'X' has no attribute '__subclasses__'

我希望得到一个字典对象之类的东西。但是我只收到一条错误消息AttributeError 'X' has no attribute '__subclasses__'。

Answer 1

您做错了三件事。

1）那不是您创建子类的方式。

子类不是类 inside 中的类，而是一个单独的类，您可以从父类/基类定义 inherits 。参见Python: How do I make a subclass from a superclass?

class Cake():
    pass

# a subclass of Cake
class Crepe(Cake):
    pass

# a subclass of Cake
class Pound(Cake):
    pass

2）您必须在父类名称而不是实例上调用__subclasses__。

an_instance_of_crepe=Crepe()

an_instance_of_crepe.__subclasses__()
# This will result in "AttributeError: 'Crepe' object has no attribute '__subclasses__'"
# This is what you are getting

Cake.__subclasses__()
# This will work, and printing out the result will give
# [<class '__main__.Crepe'>, <class '__main__.Pound'>]

3）为__subclasses__（末尾为1个“ s ”）

Answer 2

方法的名称是

__subclasses__

您写道：

__subclassess__

看到多余的“ s”吗？