[Python-3000] PEP 3100 Comments

[Guido van Rossum]

On 5/10/06, Phillip J. Eby <pje at telecommunity.com> wrote:
> Many people (including Guido, IIRC) have pointed out the severe limitations
> of your proposal, but you keep ignoring them.  As far as I can tell, it is
> you who has proposed to break Python's type system by eliminating
> attribute-based duck typing and replace it with inheritance markers.

I'm beginning to wonder if it isn't teh case that nobody here
understands Bill's proposal, and somehow in the heat of the argument
Bill hasn't been able to describe it adequately. In particular I
question my own understanding because I don't see how you *can* remove
duck typing from Python -- at least not without adding required type
declarations everywhere.

The crux of the matter seems to be how to add behavior *after* you
already have an instance of a class -- or, equivalently (?), how to
add behavior to a class when you have no control over the code that
creates instances of it.

Can you enlighten us, Bill?

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