[Python-3000] Fixing super anyone?

Jim Jewett jimjjewett at gmail.com
Tue Apr 24 01:42:21 CEST 2007

On 4/23/07, Michele Cella <michele.cella at gmail.com> wrote:

> ... having a super keyword with methods attached ... doesn't feel right

Agreed.  The goal is to *fix* super, not to make it a keyword.  Making
it a keyword might -- or might not -- be the way to do that.  A
keyword with attributes is probably not the right answer.

For What Its Worth, the longer I think about this, the more convinced
I am that the right answer is to keep it an object.  The problem is
that it has to grow even more magical than it already is, unless we
break a lot of backwards compatibility.

If we're willing to put up with the magic, then it would work to make
super syntactic sugar for

    super(__this_class__, self)

At the moment, I can't see anything wrong with this, but I have a
feeling I'm missing something about how the super object should behave
on its own.  Is there a good way (other than "being inside a method"?)
to distinguish between:

    super.__str__()     # I want to call the super-class' str method


    super.__str__()     # I want to call str(super)

> The only other option that comes to my mind is using a special attribute
> in the instance itself (like __class__, __dict__, ...):

>         self.__super__.mymethod(arg)

__class__ and __dict__ are (sort of) ordinary attributes -- they point
to a specific object.  super would probably need to be an active

    class A: ...
    class B1(A): ...
    class C1(B1): ...
    class B2(A): ...
    class C2(B1): ...

    class D(C1, C2): ...
    class E(D): ...

When an instance of E is created, the super call may well be made in
D, so you don't know the instance's class when compiling the code.

When methods in B1 make a super call for "normal" instances of C1,
they go straight to class A.  But if the instance is really an
instance of E, then they first have to loop back through C2 and C1.
So when compiling the class, you don't know which class will be next
in the mro.

So you can't do it from the class -- but you also can't do it only
from the instance.  For an instance of E, super(C1, self) and
super(B2, self) should go to different next-classes.

So you need both the instance's own true class, and the class where
the current method was defined -- but even that isn't quite enough.
You can't quite say "next in the instance's mro", because if the
method happens to be something that C2 doesn't override, then super(D,
self) should go straight to C1 -- but it still needs to look at C2 for
other methods.


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