[mod_python] 'foo.psp is not a file' 404

When a nonsense filename is entered instead of a valid template,
PSP spits out this exception:

ValueError: /local/path/foo.psp is not a file

I would like to make this return a 404 error instead. Is there an easier
way of doing it besides making my own handler, calling PSP manually, and
catching the exception?

I am using 3.1.3. (A jurassic version, I know. I got it from debian
stable packages, to try to make life easier on my webhost.)

Cheers everyone.

Greg