Type annotations missing for `assert_never`?

[bluenote10]

According to tracking issue python/mypy#5818, assert_never was introduced in typing_extensions version 4.1.0. At runtime, this clearly seems to work, which I can verify via:

python -c "from typing_extensions import assert_never"

However if I type check the code with mypy it complains at the line of the import:

error: Module "typing_extensions" has no attribute "assert_never"

I'm not sure if this an issue with typing_extensions or mypy though.

In any case, assert_never is supposed to have runtime behavior (to raise an assertion), i.e., it is not something that is supposed to be hidden behind a TYPE_ASSERTION barrier.

[AlexWaygood]

This should work fine if you upgrade to mypy 0.950 :)

[AlexWaygood]

The issue is that mypy uses typing_extensions.pyi in typeshed for typing_extensions, so if something is missing from the typeshed stub for typing_extensions, mypy doesn't know about it, even if it exists at runtime. Mypy <=0.942 uses an out-of-date version of the typeshed stub.

[bluenote10]

Indeed, works fine with mypy 0.950, thanks and sorry for the noise!

[AlexWaygood]

Indeed, works fine with mypy 0.950, thanks and sorry for the noise!

No worries!