[Python-Dev] PEP 318 - posting draft

[Bob Ippolito]

On Mar 24, 2004, at 10:59 AM, Skip Montanaro wrote:

>     Bob> For example, ZopeX3 interfaces and PyProtocols interfaces 
> both use
>     Bob> sys._getframe() introspection to add a temporary metaclass so 
> that
>     Bob> they can ...
>
>     Guido> But the use cases are certainly very *different* than those 
> for
>     Guido> function/method decorators, and should be spelled out 
> separately.
>
>     Guido> For example, I'd like to see you show in much more detail 
> how
>     Guido> class decorators could be used to replace those Zope3 hacks.
>
> Bob, if you can come up with an example or two that won't consume 
> infinite
> space, I'd be happy to add it/them to the Examples section of the PEP.

def provides(*interfaces):
     """
     An actual, working, implementation of provides for
     the current implementation of PyProtocols.  Not
     particularly important for the PEP text.
     """
     def provides(typ):
         declareImplementation(typ, instancesProvide=interfaces)
         return typ
     return provides

class IBar(Interface):
     """Declare something about IBar here"""

class Foo(object) [provides(IBar)]:
	"""Implement something here..."""

No stack introspection, no forced superclass or metaclasses, no 
side-effects on subclasses, etc.  Foo is entirely unchanged by this 
operation (in PyProtocols at least).

-bob