On Sun, Jul 31, 2016 at 6:33 AM, Gerald Britton <gerald.brit...@gmail.com> wrote: > Today, I was reading RH's Descriptor HowTo Guide at > > https://docs.python.org/3/howto/descriptor.html?highlight=descriptors > > I just really want to fully "get" this. > > So I put together a little test from scratch. Looks like this: > > class The: > class Answer: > def __get__(self, obj, type=None): > return 42 > >>>> The.Answer > <class '__main__.The.Answer'> >>>> > > but, I expected to see 42. > > So, digging deeper I read: > > For classes, the machinery is in type.__getattribute__() which transforms > B.x into B.__dict__['x'].__get__(None, B). In pure Python, it looks like: > > def __getattribute__(self, key): > "Emulate type_getattro() in Objects/typeobject.c" > v = object.__getattribute__(self, key) > if hasattr(v, '__get__'): > return v.__get__(None, self) > return v > > OK, so I copied this function, then ran it and got: > >>>> __getattribute__(The, 'Answer') > 42 > > So, what I don't get is why the "B.x into B.__dict__['x'].__get__(None, B)" > part doesn't work in my case. > > I'm sure I'm missing something here (that`s usually the case for me <:‑|) , > but what?
Obviously that __getattribute__ is not exactly like the real one. The real one looks up __get__ as a *method* of B.__dict__['x'], which requires that B.__dict__['x'] be an instance of some class that defines __get__, not the class itself. Try this: py> class Answer: ... def __get__(self, obj, type): ... return 42 ... py> class The: ... Answer = Answer() ... py> The.Answer 42 -- https://mail.python.org/mailman/listinfo/python-list
