Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Gerald Britton <gerald.britton@gmail.com>
Newsgroups: comp.lang.python
Subject: Learning Descriptors
Date: Sun, 31 Jul 2016 08:33:18 -0400
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Xref: csiph.com comp.lang.python:112134

Today, I was reading RH's Descriptor HowTo Guide at

https://docs.python.org/3/howto/descriptor.html?highlight=3Ddescriptors

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=3DNone):
            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 =3D 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 <:=E2=
=80=91|) ,
but what?