Design question about pretree classifier

[Julian]

Hello,

I've got a design problem for a classifier. To make it short: it maps
strings on strings.

Some strings have exactly one classification, some none and some more
than one.

There's a method classify(self, word) wich classifies a word. For the
first case there's no problem:

- one classification: return the value (it's a string)

But:

- none classification: return an exception or None? I think None is
better, hence its not an exception that there is no classification but
a defined state. What do you think?
- many classifications: what to do? retun a sequence of strings? raise
an exception and implement another method wich returns than the
classifications? what should I do here?

thanks for your answers!