How to define a class that can create instances of computed type/class?

[Pierre Rouleau]

Ian Bicking wrote:

>
> 
> You could also use new-style classes with a meta-class or with the
> __new__ method.  But I don't think you'll find them functionally
> different from the code you have now and it won't be worth the effort.
>

Is meta-class functionality robust?  Has it been used heavility.  It 
seems interesting and I wonder if it would'nt be better in case i wanted 
to derive a new class from it from outside the module.