exceptions beyond errors?

[e y suzuki]

i'm curious to know about ways that one could use exceptions
in python programs aside from just detecting errors.  so far
i' have read that they can be useful when a large amount of 
processing may need to be discarded, such as with branch-
and-bound and parsing algorithms.

are there additional non-error-detection cases where exceptions
are useful?

thanks in advance,
-eys