[Types-sig] QueryProtocol

[Michel Pelletier]

On Sat, 24 Mar 2001, Clark C. Evans wrote:

> Further, I still do not have a PEP number.  Either I have
> not asked correctly, am being stupid, have pissed someone
> off, or am proposing something that has already been
> rejected.  In any case, what do I do?

I suspect of the four possibilites, the first is the most likely.  Did you
read PEP 1?

> PEP: XXX
> Title: Protocol Checking and Adaptation
> Version: $Revision$
> Author: Clark Evans
> Python-Version: 2.2
> Status: Draft
> Type: Standards Track
> Created: 21-Mar-2001
> Updated: 23-Mar-2001
>
> Relationship to Python Interfaces [1] by Michel Pelletier
>
>     The relationship to this proposal to Michels proposal could
>     also be complementary.  If approved, the first two paragraphs
>     of the built-in adapt function could be changed as follows:
>
>         # first check to see if object has the exact protocol
>     >   if type(protocol) is types.InterfaceType and \
>     >       instance(obj,protocol): return obj
>         if type(obj) is types.InstanceType and \
>            obj.__class__ is protocol: return obj
>         if type(obj) is protocol: return obj
>
>         # procedure to execute on success
>         def succeed(retval,obj,protocol,can_wrap):
>     >       if type(protocol) is types.InterfaceType:
>     >           if not instance(retval,protocol):
>     >               raise "Bad __adapt__ or __prodapt__!"
>             if can_wrap: return retval
>             return obj

Actually, you would say:

  if implements(obj, protocol): return obj

An object that implements an interface is not an instance of that
interface, so 'instance' would fail (did you mean 'isinstance'?).

-Michel