> >>>> "TP" == Tim Peters <tim_one@[...].com> writes:

    TP>  As we discussed on the egroups version of this, if interfaces
    TP>  allow supplying impementation, then

    |     from InterfaceSupport import deferred
    |     class Stack(Interface):
    |         def push(self, thing): deferred()
    |         etc

    TP>  would make everyone who *claims* to implement Stack pick up
    TP>  the (presumably error-raising) Stack.push "deferred()"
    TP>  implementation if they don't supply their own (or inherit some
    TP>  other) real implementation of push.

That definitely does the trick, assuming we add something like a
NotImplementedError to the core and perhaps even a builtin function
deferred() that just raises the exception.  Half of me wants something 
a little more magical (and thus less dependent on the author to play
the right game)... okay make that 1/4 of me.. no 1/8... urg.

-Barry