list index()

[zzbbaadd at aol.com]

>
> How could it not be an exception, in the plain English sense of the
> word? Most certainly you're asking for the index because you want to do
> something with the index. If the item is not found, you have no index,
> so that's a special case that must be handled separately. There is no
> logical difference between handling that special case in an except
> clause versus handling it with an if-branch.

In my case of have done os.listdir() on two directories. I want to see
what files are in directory A that are not in directory B.
I have used exceptions in other languages and only do so on logic that
should never happen. In this case it is known that some of the files
will not be in both lists. I just want to know which ones.