class A(object):
   def __init__(self, val):
       self._val = val

   @property
   def val(self):
       return self._val

   @val.setter
   def val(self, value):
       self._val = value

class B(A):
    def __init__(self, val):
        super(B, self).__init__(val)

class B(A)
    def __init__(self, val):
        super(B, self).__init__(val)

    @val.setter(self, value):
        raise ValueError("cannot set value on B")

NameError: name 'val' is not defined

class B(A):
    def __init__(self, val):
        super(B, self).__init__(val)

    @property
    def val(self):
        return self._val

     @val.setter
     def val(self, value):
         raise AttributeError("cannot set val of B")