CIRCLE WITH A DOT

@bmispelon That would result in the same original behavior, since `__all__` controls the import behavior of `*` but not of individual variables (though I think I have seen projects that allow you to turn that kind of thing into an error via name mangling or some other hack under the hood).

@bmispelon I *think* what's happening is basically sleight of hand (though I guessed wrong at first and would not advise that people use this behavior because it can confuse us). `a.A` gets reassigned when it imports `b.A` (via `b.*`).

Autoformatting these imports would cause an error, and obviously we want these files structured this way, so setting `__all__ = []` in `b.py` is the correct fix here.