如何隐藏/删除Python继承类中的一些方法？

Question

我想在从class A继承class B class A期间隐藏一些公共方法：

class A(object):
  def someMethodToHide():
    pass

  def someMethodToShow():
    pass

class B(A):
  pass

len(set(dir(A)) - set(dir(B))) == 1

如果可能，如何在python中做到这一点？

Answer 1

塞尔丘克的建议是最好的，但有时重构太麻烦了。

因此，有些事情会导致您的同事像女妖一样尖叫并诅咒您的名字。

它通过使用metaclass hide_meta来添加重载的__getattribute__和__dir__方法。 只需将__metaclass__ = hide_meta和__excluded__ = ["list", "of", "unwanted", "attributes/methods"]设置即可将其应用于所需的类。

class hide_meta(type):
    def __new__(cls, cls_name, cls_bases, cls_dict):
        cls_dict.setdefault("__excluded__", [])
        out_cls = super(hide_meta, cls).__new__(cls, cls_name, cls_bases, cls_dict)

        def __getattribute__(self, name):
            if name in cls_dict["__excluded__"]:
                raise AttributeError(name)
            else:
                return super(out_cls, self).__getattribute__(name)
        out_cls.__getattribute__ = __getattribute__

        def __dir__(self):
            return sorted((set(dir(out_cls)) | set(self.__dict__.keys())) - set(cls_dict["__excluded__"])) 
        out_cls.__dir__ = __dir__

        return out_cls

class A(object):
    def someMethodToHide(self):
        pass

    def someMethodToShow(self):
        pass

class B(A):
    __metaclass__ = hide_meta
    __excluded__  = ["someMethodToHide"]

a = A()
print dir(a)
b = B()
print dir(b)
b.someMethodToShow()
b.someMethodToHide()

Answer 2

这是我的评论的答复形式：您可以从第三类C继承A和B。

class C(object):
  def someMethodToShow():
    pass

class A(C):
  def someMethodToHide():
    pass

class B(C):
  pass

附带说明一下，如果您想要的东西成为可能，它将打破多态性。 这个不会。

Answer 3

您可以创建一个描述符类来模拟“已删除”的属性。 然后，您可以将“待删除”名称指定为该类的实例。

这是一个完整的示例，显示了访问子类及其实例上的该属性时出现的错误/回溯。 通过引发自定义错误，回溯明确表明该属性已被有意“删除”。

In [1]: class DeletedAttributeError(AttributeError): 
   ...:     pass 
   ...:  
   ...:  
   ...: class DeletedAttribute: 
   ...:     def __set_name__(self, owner, name): 
   ...:         self.name = name 
   ...:  
   ...:     def __get__(self, instance, owner): 
   ...:         cls_name = owner.__name__ 
   ...:         accessed_via = f'type object {cls_name!r}' if instance is None else f'{cls_name!r} object' 
   ...:         raise DeletedAttributeError(f'attribute {self.name!r} of {accessed_via} has been deleted') 
   ...:  
   ...:  
   ...: class Foo: 
   ...:     def hide_me(self): 
   ...:         pass 
   ...:  
   ...:  
   ...: class Bar(Foo): 
   ...:     hide_me = DeletedAttribute() 
   ...:                                                                                       

In [2]: Foo.hide_me                                                                           
Out[2]: <function __main__.Foo.hide_me(self)>

In [3]: Bar.hide_me                                                                           
---------------------------------------------------------------------------
DeletedAttributeError                     Traceback (most recent call last)
<ipython-input-3-240c91cc1fc8> in <module>
----> 1 Bar.hide_me

<ipython-input-1-0f699423deb7> in __get__(self, instance, owner)
     10         cls_name = owner.__name__
     11         accessed_via = f'type object {cls_name!r}' if instance is None else f'{cls_name!r} object'
---> 12         raise DeletedAttributeError(f'attribute {self.name!r} of {accessed_via!r} has been deleted')
     13 
     14 

DeletedAttributeError: attribute 'hide_me' of type object 'Bar' has been deleted

In [4]: Bar().hide_me                                                                         
---------------------------------------------------------------------------
DeletedAttributeError                     Traceback (most recent call last)
<ipython-input-4-9653f0da628c> in <module>
----> 1 Bar().hide_me

<ipython-input-1-0f699423deb7> in __get__(self, instance, owner)
     10         cls_name = owner.__name__
     11         accessed_via = f'type object {cls_name!r}' if instance is None else f'{cls_name!r} object'
---> 12         raise DeletedAttributeError(f'attribute {self.name!r} of {accessed_via!r} has been deleted')
     13 
     14 

DeletedAttributeError: attribute 'hide_me' of 'Bar' object has been deleted

上面的代码适用于 Python 3.6+。