check mypy at the end of some CI runs?

[mathause]

We currently run mypy in the pre-commit hooks CI. However, this is done in an environment where no dependencies are installed. Therefore we missed the errors that pop up when running mypy with numpy 1.20 installed. (Please correct my if I misunderstood this). Should we add a new step to our CI and run mypy?

I think we should at least add this to ubuntu-latest py3.8. For more complete checks we could also go for ubuntu-latest py37-min-all-deps and upstream-dev.

[keewis]

Therefore we missed the errors that pop up when running mypy with numpy 1.20 installed.

that's true, mypy won't be able to check for changes in the type hints of dependencies if it is run by pre-commit. However, I don't think we should add mypy steps to our CI. Instead, I would prefer new jobs (not sure how many, though).

[mathause]

However, I don't think we should add mypy steps to our CI. Instead, I would prefer new jobs (not sure how many, though).

Works for me. I am also fine only testing in the ubuntu-latest py3.8 environment. I suggested ubuntu-latest py37-min-all-deps because we may now need to special-case depending on the numpy version.

xarray/xarray/core/npcompat.py

Lines 82 to 85 in 0b8ec0c

	if LooseVersion(np.__version__) >= "1.20": # type: ignore
	from numpy.typing import DTypeLike
	else:
	DTypeLike = Union[np.dtype, str] # type: ignore