Peter Otten <__pete...@web.de> wrote: > Duncan Booth wrote: > >> The descriptor protocol only works when a value is being accessed or set >> on an instance and there is no instance attribute of that name so the >> value is fetched from the underlying class. > > Unlike normal class attributes a descriptor is not shaded by an instance > attribute: > >>>> class A(object): > ... def set_x(self, value): self.__dict__["x"] = value/2.0 > ... def get_x(self): return self.__dict__["x"] * 2.0 > ... x = property(get_x, set_x) > ... >>>> a = A() >>>> a.x = 42 >>>> a.__dict__["x"] > 21.0 >>>> a.x > 42.0 >>>> A.x = "something completely different" >>>> a.x > 21.0 >
True, and in fact that's why your suggestion of using two descriptors, one at each level works. Thanks for pointing out my mistake. -- Duncan Booth http://kupuguy.blogspot.com -- http://mail.python.org/mailman/listinfo/python-list
