Originally posted on Advogato on March 22, 2004:

Fun with Python

A. M. Kuchling, in rec.arts.int-fiction, just showed me a really neat Python trick which he attributed to Michael Hudson. But first, some background:

I use a special-purpose language called Inform to write interactive fiction. It’s sort of a hybrid between standard class-based and prototype-based OO languages - there’s a shorthand to create a single object and add properties and methods to it, but if you want to create a bunch of identical objects you still need to create a class for them. It’s very handy for world modelling. Most of the specialized IF languages use the same scheme.

I’ve been thinking for a while about using a standard language - Python or Ruby, by preference - since every IF language has annoyances and weirdnesses. This involves writing a standard library for world-modelling, which is a big job. There are already a few for Python, but they’re really cumbersome compared to the Inform standard library, because creating a new object with a few specialized behaviours always involves both a new class and a new object.

Behold - prototyped Python (direct from amk’s post)! Now we get to see how well the whitespace survives it’s trip through HTML and back:

Wow. The answer to that is “not at all”. The <pre> tag appears to do precisely nothing.

Instead, the code is on my Wiki page at work. To summarize: it lets you say “class SpecialRoom(Room)” and get both a class SpecialRoom and an instance (also conveniently named SpecialRoom) automatically.

This still has a few weirdnesses. Unlike a true prototype-based language, there are still classes and objects, so you can’t directly say “issubclass(SpecialRoom, Room)” - you need to “issubclass(SpecialRoom.__class__, Room.__class__)”. I’ll need to experiment and read up some more to find out exactly how the class and the instance differ, and decide how to make it more seamless (or even if it’s worth it). This also can’t handle dynamically creating objects, which can be handled by adding a clone() method:

 def clone(self): class anon(self): pass return anon 

Except I’m not sure exactly where to put this. I tried initializing it in Prototype.__new__, which works fine but apparently isn’t correct - that’s what Prototype.__init__ is for, except it’s not actually getting called in the above code.

Still, this is lots of fun! Massive new project, here I come…

Commentary: The massive new project never materialized. I updated the wiki link to go directly to the relevant page, where you can see why - it’s a big disorganized mess of “here’s one way to do it” and “here’s another way to do it”. It was an interesting subject, though, and Python’s gotten a bunch of new features since then (decorators came out just after the original post) so I should really get back to that. It would be nice to pull it all together into a complete solution.