[Python-3000] Generic function PEP won't make it in time

[Guido van Rossum]

On 4/26/07, Bill Janssen <janssen at parc.com> wrote:
[Guido]
> > But it makes sense in some cases to insist that someone who goes
> > through the trouble of inheriting from an ABC gets an error if they
> > forget to implement one of the methods that are deemed 'essential' to
> > that ABC.
>
> This is the problem with abstract methods.  What should happen is that
> the default method (the one defined in the ABC class) gets called.
> Otherwise you're back in the morass of Java types, without effective
> mixin capability.  In Python, we need to be able to define an abstract
> class with real implementation methods -- a class that both defines an
> interface, and provides an implementation.  That means that anyone
> providing a subclass need only implement the methods that they
> override.
>
> Now, we can still have a way of marking the methods of an ABC as being
> "not implemented", which would in fact force the subclass designer to
> implement them.  But this concept should be carefully separated from
> the concept of "this method is part of the interface defined by this
> class".

Yeah. I like @abstractmethod to mean "not implemented" (except perhaps
as an end point for cooperative super calls). For the latter concept,
I propose that all methods present in an apparent ABC are considered
part of the interface, unless their name starts with a single
underscore (the latter should be considered implementation details, or
perhaps definitional details).

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)