interfaces sketch

interfaces.py

from zope.interface import implements, Interface

class ILimitedProfile(Interface):
    """
    Marker interface for basic profile functionality.
    """
    def doLimited():
        pass

class IFullProfile(ILimitedProfile):
    """
    Marker interface for full profile functionality.
    """
    def doFull():
        pass


class LimitedUser:
    implements(ILimitedProfile)

    def doLimited(self):
        return 'limited :('


class FullUser(LimitedUser):
    implements(IFullProfile)

    def doFull(self):
        return 'full!'


def doSomething(user):
    if IFullProfile.providedBy(user):
        return user.doFull()
    # they both implement ILimitedProfile as FullUser inherits the
    # implementation.
    return user.doLimited()

if __name__ == '__main__':
    print doSomething(LimitedUser())
    print doSomething(FullUser())