从Python的子类中删除属性

Question

有什么方法可以从父类中存在的子类中删除属性？

在下面的例子中

class A(object):

    foo = 1

    bar = 2

class B(A):

    pass

# <desired code here>

b = B()

assert hasattr(b, 'bar') == False

我们可以编写任何代码来使断言通过吗？

Answer 1

是的，使用描述符的魔力。请参阅我的博客文章。精简版：class nosubclasses(object):&nbsp; &nbsp; def __init__(self, f, cls):&nbsp; &nbsp; &nbsp; &nbsp; self.f = f&nbsp; &nbsp; &nbsp; &nbsp; self.cls = cls&nbsp; &nbsp; def __get__(self, obj, type=None):&nbsp; &nbsp; &nbsp; &nbsp; if type == self.cls:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if hasattr(self.f, '__get__'):&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return self.f.__get__(obj, type)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return self.f&nbsp; &nbsp; &nbsp; &nbsp; raise AttributeError例子：In [2]: class MyClass(object):&nbsp; &nbsp;...:&nbsp; &nbsp; &nbsp;x = 1&nbsp; &nbsp;...:In [3]: MyClass.x = nosubclasses(MyClass.x, MyClass)In [4]: class MySubclass(MyClass):&nbsp; &nbsp;...:&nbsp; &nbsp; &nbsp;pass&nbsp; &nbsp;...:In [5]: MyClass.xOut[5]: 1In [6]: MyClass().xOut[6]: 1In [80]: MySubclass.x---------------------------------------------------------------------------AttributeError&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Traceback (most recent call last)<ipython-input-80-2b2f456dd101> in <module>()----> 1 MySubclass.x<ipython-input-51-7fe1b5063367> in __get__(self, obj, type)&nbsp; &nbsp; &nbsp; 8&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;return self.f.__get__(obj, type)&nbsp; &nbsp; &nbsp; 9&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;return self.f---> 10&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;raise AttributeErrorAttributeError:In [81]: MySubclass().x---------------------------------------------------------------------------AttributeError&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Traceback (most recent call last)<ipython-input-81-93764eeb9948> in <module>()----> 1 MySubclass().x<ipython-input-51-7fe1b5063367> in __get__(self, obj, type)&nbsp; &nbsp; &nbsp; 8&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;return self.f.__get__(obj, type)&nbsp; &nbsp; &nbsp; 9&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;return self.f---> 10&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;raise AttributeErrorAttributeError:但是，正如评论者@delnan指出的那样，这违反了Liskov可替换性原则。我的博客文章中的动机是有根据的，因为该属性未描述对象本身。但总的来说，这首先破坏了能够进行子类化的整个目的，而这实际上就是拥有类的全部要点。顺便说一下，我的答案和@jamylak的区别在于，在@jamylak的答案中，每个子类都删除了属性。如果您制作了class C(A)，它仍将具有bar属性。在我的回答中，类本身（实际上是属性）不允许子类具有该属性，因此，一口气，所有子类都没有该属性。