ABC和@abstractmethod

Last Updated: 2023-04-30 09:00:12 Sunday

-- TOC --

在Python定义类似C++的interface（即纯虚类），需要使用ABC这个base class，以及@abstractmethod装饰器。

继承自ABC的类，就成了不能实例化的虚类，在class里面定义接口，用@abstractmethod装饰。再继续向下继承的类，就必须要实现所有基类中用@abstractmethod装饰的接口，否则代码会抛出异常。

举个例子：

from abc import ABC, abstractmethod


class xyz(ABC):

    @abstractmethod
    def show(self):
        """"""

    @abstractmethod
    def how(self):
        print('unknown...')

    def what(self):
        print('wtf...')


class X(xyz):

    def show(self):
        print('i am x...')

    def how(self):
        print('good...')


class Y(xyz):

    def show(self):
        print('i am y...')

    def how(self):
        super().how()


x = X()
x.show()
x.how()
x.what()
y = Y()
y.show()
y.how()
y.what()
# z = xyz()  # error

用@abstractmethod装饰的接口，不一定需要写body，用pass或docstring占位都OK。也可以写个body，如上how接口。

继承了ABC的xyz还可以实现concrete interface，继承后使用，如上的what接口。

xyz继承自ABC，class X和class Y继承自xyz，X和Y必须要实现show和how这两个抽象接口。Y的how接口的实现方式，采用了调用super，也OK，这就是给抽象接口写body的意义所在吧。

最后，xyz不可以实例化。

To understand the abstract class and method better, let us take an example. Suppose we have a few classes related to different items in a bookstore. Now our classes are books, stationery, and magazines. All these products are dealt with separately, so all of these classes must have a method named sale that could return the amount achieved by selling these items. So to ensure that each of these classes has a sale method, we will make an abstract class named bookstore with an abstract method Sale and will derive all the other three classes from it. Until we have made a method Sale in each of the derived classes, we would not be able to make its object, or the compiler will report an error.

用抽象类的接口定义，规范继承类必须要实现的接口。

-- EOF --

-- MORE --