python:抽象超类的实现

在python中，如何去实现一个抽象超类？
看如下代码，实现了一个简单的超类模型。

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @author : cat
# @date   : 2017/6/21.

class SuperClass:
    def method(self):
        print("method in super class.")

    def delegate(self):
        self.action()

    def action(self):
        assert False, 'sub must implement this action'


class Inheritor(SuperClass):
    pass


class Replacer(SuperClass):
    def method(self):
        print("method in replacer")


class Extender(SuperClass):
    def method(self):
        print('method in extender.')
        SuperClass.method(self)
        print('end in method')


class Provider(SuperClass):
    def action(self):
        print("action in provider.")


if __name__ == '__main__':
    for clazz in (Inheritor, Replacer, Extender, Provider):
        print("\t\t" + clazz.__name__ + " ...")
        clazz().method()

    x = Provider()
    x.delegate()

输出如下：
method in replacer
        Extender ...
method in extender.
method in suer class.
end in method
        Provider ...
method in suer class.
action in provider.

Process finished with exit code 0

这种方式实现了一个简单的抽象超类的模型，但是还不是真正的抽象超类。因为抽象，意味着该类不能被实例化。而上述的超类是可以被实例化的。

改进如下：

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @author : cat
# @date   : 2017/6/21.
from abc import ABCMeta, abstractmethod


class SuperClass(metaclass=ABCMeta):
    def method(self):
        print("method in super class.")

    def delegate(self):
        self.action()

    @abstractmethod
    def action(self):
        assert False, 'sub must implement this action'


class Inheritor(SuperClass):
    pass


class Replacer(SuperClass):
    def method(self):
        print("method in replacer")


class Extender(SuperClass):
    def method(self):
        print('method in extender.')
        SuperClass.method(self)
        print('end in method')


class Provider(SuperClass):
    def action(self):
        print("action in provider.")


if __name__ == '__main__':
    for clazz in (Inheritor, Replacer, Extender, Provider):
        pass
        # print("\t\t" + clazz.__name__ + " ...")
        # clazz().method()

    x = Provider()
    x.delegate()
    s = Inheritor()

输出如下：

Traceback (most recent call last):
action in provider.
  File "/Users/cat/PycharmProjects/py01/super-pack/inherit.py", line 49, in 
    s = Inheritor()
TypeError: Can't instantiate abstract class Inheritor with abstract methods action

通过给超类设置metaclass = ABCMeta以及，在需要让子类实现的方法上添加注解@abstractmethod即可实现抽象超类。即：让该类不能被实例化。

该类的子类上可以被实例化的，前提是，重写了超类中被@abstractmethod注解过的方法。

参考资料：《Learning Python》