Inheritance confusion

[Hook]

Thanks to everyone who replied. Kay and Mark put me on the right track 
immediately. Ben is quite right - the fragment that I posted couldn't 
have given that error, but I didn't want to post the whole thing - 
perhaps wrongly, I thought it wouldn't help clarify what I thought the 
problem was. And that was the real issue - I had managed to convince 
myself that I had a naming problem in one of my own modules somewhere.

If anyone is interested in the background, I'm a long time Perl 
programmer trying to learn Python by converting a small set of standard, 
locally developed Perl libraries. It's an edifying experience, and I can 
understand why some colleagues like Python so much.

Again, thanks for the help, it's appreciated.

Hook