You're right. The [changelog] for Python 3.7 states: > [bpo-32670]: Enforce [PEP 479] for all code. This means that manually raising a StopIteration exception

You're right. The [changelog] for Python 3.7 states: > [bpo-32670]: Enforce [PEP 479] for all code. This means that manually raising a StopIteration exception from a generator is prohibited for all code, regardless of whether ‘from __future__ import generator_stop’ was used or not. [changelog]: https://docs.python.org/3.7/whatsnew/changelog.html#id115 https://docs.python.org/3.7/whatsnew/changelog.html#id115 [bpo-32670]: https://bugs.python.org/issue32670 https://bugs.python.org/issue32670 [PEP 479]: https://www.python.org/dev/peps/pep-0479/ https://www.python.org/dev/peps/pep-0479/