强制子类覆盖父类的方法 [英] Force child class to override parent's methods

问题描述

假设我有一个带有未实现方法的基类，如下所示:

Suppose I have a base class with unimplemented methods as follows:

class Polygon():
    def __init__(self):
        pass

    def perimeter(self):
        pass

    def area(self):
        pass

现在，假设我的一位同事使用 Polygon 类创建一个子类，如下所示:

Now, let's say one of my colleagues uses the Polygon class to create a subclass as follows:

import math

class Circle(Polygon):
    def __init__(self, radius):
        self.radius = radius

    def perimeter(self):
        return 2 * math.pi * self.radius

(H/Sh)e 忘记实现 area() 方法.

(H/Sh)e has forgotten to implement the area() method.

如何强制子类实现父类的area()方法?

How can I force the subclass to implement the parent's area() method?

推荐答案

这可能是你的父类:

class Polygon():

    def __init__(self):
        raise NotImplementedError

    def perimeter(self):
        raise NotImplementedError

    def area(self):
        raise NotImplementedError

虽然问题只会在运行时被发现，但当子类的一个实例试图调用这些方法之一时.

although the problem will be spotted at runtime only, when one of the instances of the child classes tries to call one of these methods.

另一个版本是使用 abc.abstractmethod.

a different version is to use abc.abstractmethod.

from abc import ABC, abstractmethod
import math


class Polygon(ABC):

    @abstractmethod
    def __init__(self):
        pass

    @abstractmethod
    def perimeter(self):
        pass

    @abstractmethod
    def area(self):
        pass

class Circle(Polygon):
    def __init__(self, radius):
        self.radius = radius

    def perimeter(self):
        return 2 * math.pi * self.radius

#    def area(self):
#        return math.pi * self.radius**2


c = Circle(9.0)
# TypeError: Can't instantiate abstract class Circle
#            with abstract methods area

如果没有实现所有方法，您将无法实例化 Circle.

you will not be able to instantiate a Circle without it having all the methods implemented.

这是python 3 语法；在 python 2 你需要

this is the python 3 syntax; in python 2 you'd need to

class Polygon(object):
    __metaclass__ = ABCMeta

---

还要注意，对于二进制特殊函数 __eq__(), __lt__(), __add__(), ... 最好返回 NotImplemented 而不是引发 NotImplementedError.

这篇关于强制子类覆盖父类的方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！