[Python-3000] Iterators for dict keys, values, and items == annoying :)

[Adam DePrince]

On Thu, 2006-03-30 at 12:05 +1200, Greg Ewing wrote:
> Adam DePrince wrote:
> 
> > SetView implements:
> >    .__contains__
> >    .add
> >    .discard  
> >    .__len__
> 
> But what would there be to inherit from the mixin?
> Each view class will have entirely its own implementation
> of these, depending on the details of the base object.
> Inheritance in Python is *entirely* about implementation
> inheritance, not interface inheritance.
> 
> > By allowing dict.keys() to announce "I'm a SetView"
> 
> If you mean to make it possible for code to do
> 
>    if isinstance(something, SetView):
>      ...
> 
> that's another thing that Python tries to stay away
> from as much as possible.
> 
> If what you're proposing is purely a conceptual
> classification, I still think it's far too
> elaborate. Anyone reading such a specification is
> going to have their eyes glaze over within a few
> milliseconds.

Only if they examine Python from the perspective of Python ... from a
C-api perspective there are certain advantages to lumping things into
interfaces, and in the C-API there is no inheritance.  

The manifestation of these interfaces would be in the naming
convention ... __len__ would become part of the View (note the PEP
changed since the above SetView implementation description) interface
and called PyView_len.  

I'm trying to address both perspectives here; the user is free to toss
these interfaces and code just knowing what methods to provide trusting
that everything will quack right.   

> 
> --
> Greg
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