Mypy failures with MultiIndex

[jsignell]

What is your issue?

As seen in https://github.com/pydata/xarray/actions/runs/13771308824/job/38510332904?pr=10109 and https://github.com/pydata/xarray/actions/runs/13771399760/job/38510636156?pr=10062

 xarray/core/indexes.py: note: In member "stack" of class "PandasMultiIndex":
xarray/core/indexes.py:1051: error: Argument 2 to "MultiIndex" has incompatible type "list[ndarray[Any, dtype[Any]]]"; expected "Sequence[Sequence[int]]"  [arg-type]
Generated Cobertura report: /home/runner/work/xarray/xarray/mypy_report/cobertura.xml
xarray/core/indexes.py: note: In member "from_variables_maybe_expand" of class "PandasMultiIndex":
xarray/core/indexes.py:1123: error: Argument 2 to "MultiIndex" has incompatible type "list[Iterable[int]]"; expected "Sequence[Sequence[int]]"  [arg-type]
xarray/core/coordinates.py: note: In member "to_index" of class "AbstractCoordinates":
xarray/core/coordinates.py:186: error: Argument 2 to "MultiIndex" has incompatible type "list[ndarray[Any, dtype[Any]]]"; expected "Sequence[Sequence[int]]"  [arg-type]
xarray/core/groupby.py: note: In member "factorize" of class "ComposedGrouper":
xarray/core/groupby.py:530: error: Argument 1 to "from_product" of "MultiIndex" has incompatible type "Generator[ndarray[Any, Any], None, None]"; expected "Sequence[Any]"  [arg-type]
xarray/tests/test_dataset.py: note: In member "test_drop_indexes" of class "TestDataset":
xarray/tests/test_dataset.py:2926: error: List item 0 has incompatible type "list[int]"; expected "tuple[Hashable, ...]"  [list-item]
xarray/tests/test_dataset.py:2926: error: List item 1 has incompatible type "list[int]"; expected "tuple[Hashable, ...]"  [list-item]
xarray/tests/test_dataset.py: note: In member "test_rename_multiindex" of class "TestDataset":
xarray/tests/test_dataset.py:3222: error: List item 0 has incompatible type "list[int]"; expected "tuple[Hashable, ...]"  [list-item]
xarray/tests/test_dataset.py:3222: error: List item 1 has incompatible type "list[int]"; expected "tuple[Hashable, ...]"  [list-item]
Installing missing stub packages:
/home/runner/micromamba/envs/xarray-tests/bin/python -m pip install types-openpyxl


Generated Cobertura report: /home/runner/work/xarray/xarray/mypy_report/cobertura.xml
Found 8 errors in 4 files (checked 177 source files)

[benbovy]

Thanks for the report @jsignell.

The multiindex errors seem to result from pandas-dev/pandas-stubs#1126. I wonder if Sequence defined for some arguments of the MultiIndex constructors isn't too restrictive. This prevents using numpy arrays or iterables which we are using here and which seems valid (see also pandas-dev/pandas-stubs#1158).

[jsignell]

Yeah that makes sense. Maybe it makes sense to pin the stubs to get tests passing.