Explore adding static typing

[di]

We should determine a way that we can gradually add static typing (and ensure that we're able to assert that it is correct in CI) without introducing a single massive PR.

[fizyk]

mypy has configuration options that would allow doing that gradually

https://mypy.readthedocs.io/en/stable/config_file.html

We could either include paths that got converted or exclude those that do not (this would require all new ones to already be typed)

[miketheman]

I'm interested in this kind of work.

A few questions/decisions arise at this juncture:

• Is mypy considered a lint tool, or a testing tool? (for requirements inclusion) I think lint - from the mypy docs:

  As mypy is a static analyzer, or a lint-like tool, ...

• Is there a particular entry point or an area of focus? We can also follow the recommended path
• Where do we want to configure mypy? I'm partial to pyproject.toml, but that's not currently mounted to the developer container - should we mount that as well?

[di]

Is mypy considered a lint tool, or a testing tool? (for requirements inclusion)

I think this belongs with our linters.

Is there a particular entry point or an area of focus? We can also follow the recommended path

There are some existing types that @fizyk did that could be a good starting point. Other good starting points would be our more critical codepaths.

Where do we want to configure mypy? I'm partial to pyproject.toml, but that's not currently mounted to the developer container - should we mount that as well?

Using pyproject.toml is preferable, and this should already be getting included in the dev container, as there's configuration for other linters and pytest in there as well

[miketheman]

I think this can be closed now, as we have a mechanism for adding more types as gradually as we want to now.