... under what circumstances is this ever None?

Yeah arguable. In the other PR they were discussing about this because it may not exist at all which cannot be expressed. Or can it?

Actually looking closer, sometimes this can be at least a _NamespacePath (which is a MutableSequence).

Oh ok. Like option to list[str] | MutableSequence?
I coulnd't find _NamespacePath tho.

Thanks for reviewing! 🙏

We don't have a way to express "__path__ may be missing", but I don't think it's a problem in practice:

• __file__ is missing in obscure corner cases. It would be good if the type checker warned about not checking that.
• __path__ is missing usually (specifically, for imported .py files). If you know anything at all about __path__, you are probably aware of this, or you will find out by doing some very basic testing, without checking corner cases.

Diff from mypy_primer, showing the effect of this PR on open source code:

core (https://github.com/home-assistant/core.git)
+ homeassistant/loader.py:298: error: unused "type: ignore" comment

edgedb (https://github.com/edgedb/edgedb.git)
+ edb/schema/std.py:41: error: unused "type: ignore" comment
+ edb/schema/std.py:42: error: unused "type: ignore" comment
+ edb/schema/std.py:43: error: unused "type: ignore" comment
+ edb/schema/std.py:44: error: unused "type: ignore" comment

a pleasure 🙇‍♀️