Question

我有一个定义了几个空方法的基类。我想强制/强制在子类中定义这些方法，并在初始化时使它崩溃，以防它们被覆盖。

例如：

class Shape:
    def __init__(self, name):
        self.name = name
    def number_of_edges(self):
        pass  # method HAS TO be overloaded in subclass

class Triangle(Shape):
    def __init__(self, name):
        super(Triangle, self).__init__()

    def number_of_edges(self):
        return 3

似乎Python方式是提出NotImplementedError：

def number_of_edges(self):
    raise(NotImplementedError)

但是，在类实例化期间提前崩溃并检测缺少实现可能是有益的。为什么这不是默认值，可以这样做吗？

Answer 1

使用abc module创建一个抽象基类。

import abc

class Shape(object):
    __metaclass__ = abc.ABCMeta

    def __init__(self, name):
        self.name = name

    @abc.abstractmethod
    def number_of_edges(self):
        pass

使用@abc.abstractmethod decorator修饰的任何方法都会触发TypeError例外：

>>> import abc
>>> class Shape(object):
...     __metaclass__ = abc.ABCMeta
...     def __init__(self, name):
...         self.name = name
...     @abc.abstractmethod
...     def number_of_edges(self):
...         pass
...
>>>  
>>> class Triangle(Shape):
...     pass
... 
>>> Triangle('t3')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Can't instantiate abstract class Triangle with abstract methods number_of_edges
>>> class Triangle(Shape):
...     def number_of_edges(self):
...         return 3
... 
>>> Triangle('t3')
<__main__.Triangle object at 0x105f3b8d0>

Answer 2

您可以使用Abstract Base Class;

import abc
class Shape:
    __metaclass__ = abc.ABCMeta   

    def __init__(self, name):
        self.name = name

    @abc.abstractmethod
    def number_of_edges(self):
        pass  # method HAS TO be overloaded in subclass

现在，如果Triangle类没有覆盖number_of_edges方法，它将引发异常。

Python基类，它在实例化时强制使用抽象方法定义

2 个答案: