Am I missing something with Python not having interfaces?

[Luis Zarrabeitia]

On Wednesday 07 May 2008 03:19:30 pm Daniel Marcel Eichler wrote:
> Am Dienstag 06 Mai 2008 16:07:01 schrieb Mike Driscoll:
>
> Well, no. It's a litte different. Interfaces force to implement methods.
> Simple inheritance with method-stubs can't garantee that a specific
> method is reimplementat in a sub-class. Interfaces work at
> compile-time, while method-stubs raise at their first call, so in worst
> case, never (when the developer is available).

<Pseudo-java code>
class MyClass implements MyInterfaceWithPassMethod {
     function Pass() {
     }
}
</pseudo-java code>

There you have it, interfaces are not enough to ensure that the implementors 
actually implement the methods. They are useful for warning at compile time 
if there is a missing method, but nothing more. I believe you could achieve a 
very similar warning in python using some kind of Interface metaclass (too 
lazy right now to hack a proof of concept, but it looks doable).

I actually like the Interface concept... as portrayed by zope.Interfaces and 
pyprotocols (not the same thing, but I like them), and the ABCs (these, not 
so much). But Java interfaces are barely a replacement for multiple 
inheritance+abstract methods.

> That's the point. Interfaces garantee that a duck is a duck, an not only
> a chicken that quack.

Not really. (See the NotImplementedExceptions in .NET 1.1 and window forms, 
and/or their TabbedControl/TabPage background color attribute. Can't find 
them now, as I don't have .NET anymore, but I consider that an example of why 
the static typing are... overrated)

-- 
Luis Zarrabeitia (aka Kyrie)
Fac. de Matemática y Computación, UH.
http://profesores.matcom.uh.cu/~kyrie