Nifty example, but this is why we have integration test suites.

PyPy, jython, ironpython etc all had/have incompatibilities as the language evolves and as they work out the quirks in their respective runtimes.

This isn't compatible with cpython (afaik, none of the other runtimes have ever been COMPLETELY compatible, but this is much further off), but hell, it's pretty awesome.

As an aside, I'd shoot anyone who did that ^^ without a pretty amazing explaination.