pypy Exception games

pypy_exc.py

>>>> class MyException(Exception):
....    def pr(self):
....       print 'hi'
>>>> __builtins__.FutureWarning = MyException
>>>> try:
....    raise FutureWarning
.... except FutureWarning as fw:
....    fw.pr()
....
hi
>>>> __builtins__.KeyError = MyException
>>>> try:
....    {}['nope']
.... except KeyError as ke:
....    ke.pr()
....
Traceback (most recent call last):
  File "<console>", line 2, in <module>
KeyError: 'nope'

# FutureWarning was caught because I threw it in Python, 
# but KeyError wasn't because it was thrown in RPython. :/