I can have a poke at the __future__ import tonight, but my main concern is memory management - I'm not sufficiently familiar with the exception handling calls to be sure that I'm neither leaking nor over-freeing anything. There's also a secondary concern that the tracebacks aren't quite right at the moment, possibly caused by a muck-up in the exception chaining.

>>> def f(): raise StopIteration
>>> def g(): yield f()
>>> next(g())
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: generator raised StopIteration

There's no indication of which function/line caused the exception, which would be _extremely_ helpful. If someone else can look into that at some point, I'd appreciate the assistance.