[Tutor] Inheritance, superclass, ‘super’

[Ben Finney]

Alan Gauld <alan.gauld at btinternet.com> writes:

> On 01/07/15 03:48, Ben Finney wrote:
> > Alan Gauld <alan.gauld at btinternet.com> writes:
> >
> >> Whilst I agree with the general use of super I'm not sure what
> >> the MRO resolution has to do with this case?
> >
> > When accessing the superclass, the MRO is always relevant
>
> Can you explain that?
> If I access a class explicitly

As explained on other posts: You're not getting “the superclass” if you
do that. Knowing what the superclass is requires run-time determination
of the MRO.

> If MyList is included in a MI lattice that doesn't change the fact
> that MyList inherits directly from list.

Correct. The distinction being drawn here is between “the class from
which MyList directly inherits” versus “the superclass of this class”.
They are not the same, in multiple inheritance.

To refer to the direct parent class, yes it's simple enough to hard-code
that. But that's not the same thing as accessing the superclass, which
must be determined at run-time.

> That depends on what you mean by break it., MI should allow the
> inheriting class to specify which, if any, of its direct superclasses
> methods are invoked.

That “should” is contrary to Python's collaborative multiple inheritance
model. Instead, multiple inheritance in Python entails that any class
should allow the methods of the same name, in all superclasses of this
one, to execute in the sequence determined by ‘super’.

So, if you want behaviour as you describe there, you want something that
Python's mutliple inheritance explicitly won't give you.

-- 
 \        “Intellectual property is to the 21st century what the slave |
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_o__)                                                                  |
Ben Finney