mypy strict mode

[jorenham]

This configures mypy to run in "strict mode", which according to mypy --help enables the following flags:

--warn-unused-configs, --disallow-any-generics, --disallow-subclassing-any, --disallow-untyped-calls, --disallow-untyped-defs, --disallow-incomplete-defs, --check-untyped-defs, --disallow-untyped-decorators, --warn-redundant-casts, --warn-unused-ignores, --warn-return-any, --no-implicit-reexport, --strict-equality,
--strict-bytes, --extra-checks

Enabling this caused a bunch of typing errors to surface, which are now also fixed.

Most of these are related to bytes/bytearray/memoryview not being assignable to each other. So I used their common denominator, collections.abc.Buffer, or rather its backport from typing_extensions (which is always available if TYPE_CHECKING because typeshed conveniently lies that it's part of the standard library).

[radarhere]

I don't see anything at https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-strict that mentions follow_imports? What was the thinking behind changing this?

[jorenham]

That's right, follow_imports is unrelated to --strict. It's just unnecessary to suppress those import errors.

[radarhere]

The changes here should be re-evaluated after #9414's debate about Python versions is resolved.

[jorenham]

Anything I can do to help with that?

[radarhere]

#9414 (comment)

Is there authoritative guidance on best practices here?

The only thing I can think of is to ask someone at mypy for their official view on whether we need to run mypy against the oldest supported Python, newest Python, or everything in between.

[jorenham]

#9414 (comment)

Is there authoritative guidance on best practices here?

The only thing I can think of is to ask someone at mypy for their official view on whether we need to run mypy against the oldest supported Python, newest Python, or everything in between.

@JukkaL sorry to bother you, but could I redirect this question to you?