programming unlimited "categories" in python ?

[Terry Reedy]

"Stephen" <shriek at gmx.co.uk> wrote in message
news:97ae44ee.0110230529.5c33dd83 at posting.google.com...
> > > I'm developing a catalog application (storing its data in a
> > > relational database), where catalog entries are categorized
> > > by one or more categories/subcategories.

>From the above and your example catagories, I mistakenly assumed that
you wanted to store relational data in your relational database, and
described how to do that.  Instead, it seems, you want to simulate a
dynamically adjustable hierarchical database using an RDBM as the data
manager behind the scenes.

> > >  It would be nice to have "unlimited" levels of subcategories
...
> Thank you for the advice, Terry.  Sorry if I'm being obstinate,
> but I think the problem is a little less simplistic than it first
> appears.

Definitely (and wanting a solution to your actual problem, now better
explaned, is not really being obstinate).

> Let's look at the everyday addressbook in Act! or Outlook ?

I'm not familiar with either, or any similar programs.  My closest
point of reference is the Windows registry.  Otherwise, my experience
is 'limited' to static schema (from users viewpoint) relational
databases.

> How would you create unlimited levels of categorisation
> and unlimited numbers of subcategories ?

Interesting question.  To say much more, I'd need more specification.
Such as, do you want to do search and selection with the RDBM (mostly
off the disk) or with Python (possibly in memory)?  If with the RDBM,
I think my original comment stands:  if you want to efficiently (and
scalably) search and retrieve on any level of the hierachy, then you
mush explicitly store each level with each item.  An alternative would
be an expandable tree index structure written, in this case, in
Python.

Terry J. Reedy