It doesn't bother me that Python programmers can write unportable code, what with consenting adults and all that. Further the implementation of PEP 3151 in 3.3 allows specific exceptions to be caught, e.g. FileNotFoundError.  I can't see anybody allowing the exception number being changed to the symbolic string or even omitted completely, so I'd recommend this is closed unless there's an extremely good reason not to do so.