programming unlimited "categories" in python ?

[Stephen]

> This is a classic SQL problem, which most often manifests itself in
> bill-of-materials processing in which parts are components of other parts,
> and so on down to many levels. One reference to solutions can be found
> towards the end of
> 
>      http://www.dbmsmag.com/9603d06.html
> 
> It's one of those problems that has an "obvious" solution, which is very
> non-obvious until you see it.

Excellent Steve. This is precisely what I was looking for.
(circa 1996 too - knew this had to have a standard/classic solution)

Stephen.