Pie-thon has Exception objects. We'll need such beasts too. So:
1) How do we "translate" Python classes? Properties only? Or
    full ParrotClass objects?
2) We'll need to classify our exceptions somehow so that we can model an
exception class hierarchy. We'll also need to catch specific exceptions
properly so that:

   # from b1.py - pseudo code
   try:
     n = self.P0(n+1)   # recursive
   except RuntimeError:
     # pass
   return n

can catch specific exceptions.

Comments welcome.
leo