I would propose using "hasattr" to check for the existence of awake, respond, and sleep, and removing the assert statement. The RuntimeError that results could have a much better error message than the assert would give us, anyhow.
But I'm curious on Chuck's take on removing the assert statement. I somehow have a feeling that he has an opinion on this, maybe because it was discussed before? - Geoff > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] > Sent: Monday, April 08, 2002 3:31 PM > To: [EMAIL PROTECTED] > Subject: Re: [Webware-discuss] Allowing delegation in servlets > > > On Mon, Apr 08, 2002 at 02:43:37PM -0400, Geoffrey Talvola wrote: > > > My first attempt failed because line 183 of ServletFactory is: > > > > > > assert issubclass(theClass, Servlet) > > > > > > Anyway, I'd like to argue for the removal of the assertion in > > > ServletFactory, since it is denying use of a very powerful, > > > and arguably > > > better technique than inheritance. In any case, assertions > > > can be optimized > > > away in .pyo files, so that the presence of the assertion > > > statement is of > > > questionable value... > > > > I think the assertion is there to help out the Webware user > who forgets to > > have their servlet inherit from Servlet. I assume that > mistake happens > > relatively frequently. I know I've done it once or twice. > Without the > > assertion (which pinpoints the problem pretty clearly), > presumably you would > > wind up with a traceback somewhere else in the guts of > Appliction.py that > > would be less obvious to track down, especially for a casual user. > > > > Now you've identified a legitimate use for a servlet not > derived from > > Servlet. So you want to remove the assertion, but that > would hurt casual > > Webware users hwo might forget the base class. So maybe > there should be an > > option "AllowServletsNotDerivedFromServlet" that defaults > to 0, but you can > > just flip the switch and it skips the assertion? I would > imagine this to be > > documented as "for experts". > > If a servlet must always subclass Servlet, or at least we pretend to > require that for the default case, the exception should be > changed from > AssertionError to something else. AssertionError mean "I" made an > error. Other exceptions mean "you" made an error. > > But perhaps we need to rethink what are the requirements for servlets. > At minimum, awake/respond/sleep methods. This sounds like an > interface. > Since Python doesn't have interfaces (yet), we've been using > "must be a > subclass of Servlet" as a substitute. > > The simplest way to avoid the issubclass test and yet not introduce an > esoteric option like AllowServletsNotDerivedFromServlet would be to > test explicitly for the required features: > > if not hasattr(theClass, 'respond'): raise RuntimeError(...) > > try: > theClass.respond > except AttributeError: > raise RuntimeError(...) > > if not hasattr(theClass, 'respond') or \ > type(theClass.respond) != types.MethodType: > raise RuntimeError(...) > > requiredMethods = 'awake', 'respond', 'sleep' > for methMame in requiredMethods: > try: > meth = getattr(theClass, methName) > if type(meth) != types.MethodType: > raise RuntimeError("not a method...") > except AttributeError: > raise RuntimeError("method doesn't exist...") > > > -- > -Mike (Iron) Orr, [EMAIL PROTECTED] (if mail problems: [EMAIL PROTECTED]) > http://iron.cx/ English * Esperanto * Russkiy * > Deutsch * Espan~ol > > _______________________________________________ > Webware-discuss mailing list > [EMAIL PROTECTED] > https://lists.sourceforge.net/lists/listinfo/webware-discuss > _______________________________________________ Webware-discuss mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/webware-discuss
