STINNER Victor> Do you need the original traceback? Why not only raising 
the exception?

If the exception was captured in one stack, and is being re-raised in 
another. It would be more useful to see the two stacks appended instead 
of just the place where it was re-raised (or the place where it was 
raised initially, which is what a string would get you - not to mention 
the inability to catch it).