Question about accessing class-attributes.

[Michele Simionato]

Alex Martelli <aleax at aleax.it> wrote in message news:<XFhsa.30684$3M4.874686 at news1.tin.it>...

> <snip various objections not related to what I am trying to say>

> I don't see any pedagogical utility in claiming there is one
> distinguished superclass.  The super will quite happily be a
> proxy to methods in other and completely unrelated classes if
> the methods don't happen to exist directly in the one and
> only one you want to present as "THE" superclass.  Therefore,
> it seems to me that said hypothetical class attribute would
> only breed confusion and resulting errors.
> 
> 
> Alex

Clearly, we are having some misunderstanding ( I don't know at
which level). I do think the concept of superclass (even in a multiple
inheritance situation) is well defined, useful and not confusing at all. 
Let me try to explain.

Consider your example:
 
class A(object): a = 23 
class B(object): a = 45 
class C(A, B): a = 67 

which is the typical diamond diagram:


                           object
                          /      \
                          A       B
                           \     /
                              C

Now we want to explain to the newbie what super(A, C).a returns.

To this aim, we look at the MRO of C, which is the list [C,A,B,object].
Then, we define the superclass of A with respect to the MRO of C, 
as the class following A in the list [C,A,B,object]. In this case the
superclass is B. Then we say to the newbie that super(A,C).a is *ideally*
equivalent to B.a and therefore it returns 45.

If super had a __superclass__ attribute I could say to the newbie

super(A,C).a <=> super(A,C).__superclass__.a <=> B.a 

Of course, the equivalence would not be exact in subtle cases,
i.e. when B does not have an 'a' attribute, nor it inherits it,
but it has (or inherits) a __getattr__ defining 'a' (as Bjorn 
pointed out)
Still in the typical case there would be equivalence. 

I made my point clear, now ? At least, this is the way I followed
to teach to myself how super works.

Ciao,

                                                    Michele