I mean I think python's module's are kind of stupid, but even as someone who literally doesn't every use python's module system, my very first thought here was "I bet strict mode is requiring explicit exports in __all__"

And indeed[0] that's the case. It makes perfect sense that the abstract machine of typed python does not allow everything that the abstract machine of untyped python does, and java would error on trying to use a private class or method just the same.

[0]: https://mypy.readthedocs.io/en/latest/command_line.html#cmdo...