py3: catch StopIteration from next() in generatorset IIUC, letting the StopIteration through would not cause any bugs, but not doing it makes the test-py3-commands.t pass. I have also diligently gone through all uses of next() in our code base. They either: * are not called from a generator * pass a default value to next() * catch StopException * work on infinite iterators * request a fixed number of items that matches the generated number * are about batching in wireproto which I didn't quite follow I'd appreciate if Augie or someone else could take a look at the wireproto batching and convince themselves that the next(batchable) calls there will not raise a StopIteration.