This commit implements PEP479 which disallows raising StopIteration inside a generator to signal that it should be finished. Instead, the generator should simply return when it is complete. See https://www.python.org/dev/peps/pep-0479/ for details.
From now on, all new tests must use underscore. Addresses issue #727.
Scott Shawcroft
Damien George
Rami Ali