super() doesn't get superclass

[Ben Finney]

Evan Klitzke <evan at yelp.com> writes:

> On Tue, 2007-09-18 at 14:15 +1000, Ben Finney wrote:
> > Why does the documentation of 'super' say that it returns the
> > superclass when *that's not true*? It doesn't return the
> > superclass, it returns the next class in the MRO, whether that's a
> > superclass or not.
> 
> The next class in the MRO _is_ a superclass. Maybe not the way
> you've defined it in your own code, but certainly of the new class
> you created with MI.

If I define a class hierarchy as follows::

    class A(object): pass
    class B(object): pass
    class C(A): pass
    class D(B): pass

is it true to say that "D is a superclass of A"? No, because they're
entirely unrelated except that they inherit from 'object'. The
superclass of 'A' is 'object'.

How about this:

    class E(C, D): pass

In this instance, the MRO now has D following A; but the superclass of
'A' is still 'object'.

You seem to be saying that now suddenly D *is* a superclass of
A. That's certainly not what users will think of when they think
"superclass" though.

> > Actually, even that's not true. The error message "AttributeError:
> > 'super' object has no attribute 'bazfunc'" makes it clear that
> > 'super' actually returns not the superclass, but a 'super' object,
> > whatever that's supposed to be.
> 
> No, super really does return a class. What makes you think that
> super returns a special sort of object?

    >>> super(A)
    <super: <class 'A'>, NULL>
    >>> super(A).__class__
    <type 'super'>

What I expect, incidentally, is that a function documented as "returns
the superclass of 'type'" would actually return that class (in this
case, the type 'object'), not an object of 'super' type.

> > After reading the rest of the article, I'm amazed that 'super' as
> > currently implemented is in Python at all. I agree with the author
> > that it's useless unless *everyone* uses it for *everything*, and
> > even then it's pretty limited.
> 
> I don't see what the problem is. If you don't use super, then you can
> break the inheritance chain

I don't want to break the inheritance chain. I want the superclass,
not the "next class in the MRO".

Orthogonally to that, I think it's madness to write a function for
"return the next class in the MRO for 'type'" and document it as
"return the superclass of 'type'".

Am I mistaken in thinking that "superclass of foo" is equivalent to
"parent class of foo"? If so, I'd lay heavy odds that I'm not alone in
that thinking.

-- 
 \           "Laugh and the world laughs with you; snore and you sleep |
  `\                                                alone." —anonymous |
_o__)                                                                  |
Ben Finney