> A use case here is in a stack trace or a debugger where an error
> occured. For example does this come from an egg? And if so, which one? 
> 
> Perhaps I have missed something in PEP 302, or perhaps this is defined
> elsewhere. Please elucidate.

Please understand that the bug tracker is not a place to ask questions,
or get help. If you make a bug report, *ALWAYS* follow this pattern:

1. this is what I did
2. this is what happened
3. this is what I would have expected instead

If you want to get help in doing something that you don't know how to
do, or need elucidation, use python-list@python.org. If you are
proposing a new feature, and want to discuss the design of it, use
python-dev@python.org; you might be told to write a PEP if the feature
is more complex.

I'm going to close this report as invalid.