Okay so I take back my first proposal of restoring the filters in the test suite, which would bring us back to <https://bugs.python.org/issue18383#msg232451>.

Also, my second proposal of setting a flag doesn’t look so easy either. The “_warnings” C module caches the filters list in a static variable between module reloads, so it is not so easy to keep a flag recording whether the “warnings” Python module needs to initialize it. I started on a patch, but discovered I would have to make uncomfortable changes to the C module.

So unless anyone has any better ideas, I think Alex’s patch is as good and practical enough. And yes Victor’s change does fix the other half of the problem.