Configuration options for mypy

[alexdewar]

As discussed in the meeting, there are various options that one can enable in mypy. The options can be added to a section in pyproject.toml like so:

[tool.mypy]
ignore_missing_imports = true
disallow_untyped_calls = true
disallow_untyped_defs = true
disallow_incomplete_defs = true

Those options are ones that I'm using for another project and they may not all suit you. The one that I'd strongly recommend is ignore_missing_imports = true. It stops mypy from giving errors when types for external libraries are unknown (as is very commonly the case!). The other options essentially just make type annotations mandatory everywhere -- otherwise mypy will only check that annotations are correct, not whether they are present.

[jacobcook1995]

Don't know if this is the right place for this (if not I can make a different discussion point), but if we decide to turn off the requirement of docstrings for testing functions the way we did it in a different project was to add

per-file-ignores =
    test/test_*.py: D103

under the [flake8] heading of the setup.cfg file. I think if we want to turn off docstrings at the top of testing scripts as well we would also have to add D100 in there.

[alexdewar]

That's useful but I think you're right that this isn't the right place for it 😉. You could open a new discussion or it could be a new issue.

[jacobcook1995]

Turning on the ignore_missing_imports feels pretty essential to me. With the other options I can see the value in us forcing ourselves to always provide type hints. I guess if we turn those options on it's probably important to do so before a significant amount of code has been committed to the repo, because otherwise whoever turns the option on might get flooded with mypy errors?

[alexdewar]

Agreed. I use ignore_missing_imports for my projects.

[davidorme]

I agree with forcing us to provide type hints.

On ignore_missing_imports , one issue is that some packages missing typing imports have stubs providing typing via typeshed, so for example although requests might be untyped, we should make use of types_requests. Does ignore_missing_imports basically hide having to make that decision and leave us with typing we could check but are not? If we leave it turned off, then we either add the types stub to the dev requirements or have to manually # type: ignore, making it explicit?

[alexdewar]

I think mypy is aware of typeshed. You can install the missing type stub packages with the --install-types option.

[davidorme]

The docs here are not clear on whether using ignore_missing_imports = true then suppresses warnings about missing stubs. That page does say that globally ignoring is a choice of last resort and there is a mechanism to configure mypy to globally ignore specific packages.

For now, I'm tempted to leave off the global setting and be more picky to begin with. We can relax it if needed later.