[Bug] ModuleNotFoundError with xarray >= v2025.03.0

[jskrzypek]

Xarray's v2025.03.0 release last week seems to have included a breaking change that results in cf_xarray erroring out on import.

After I updated our dependencies today, xarray got bumped from v2025.01.2 to v2025.03.0, and I starting seeing this error in my stack trace:

my/code/common/io.py:16: in <module>
    from cf_xarray import decode_compress_to_multi_index, encode_multi_index_as_compress
.venv/lib/python3.11/site-packages/cf_xarray/__init__.py:2: in <module>
    from .accessor import CFAccessor  # noqa
.venv/lib/python3.11/site-packages/cf_xarray/accessor.py:27: in <module>
    from xarray.core.arithmetic import SupportsArithmetic
E   ModuleNotFoundError: No module named 'xarray.core.arithmetic'

When I pin the constraint for xarray to xarray >= 2023.10.1, < 2025.3.0 I no longer see this issue, so I have a good workaround, just wanted to make sure to report in case you have the appetite to fix the issue or other followers encounter the same problem.

You can see the problematic file move in question here (xarray/core/arithmetic.py → xarray/computation/arithmetic.py). There may be others.

[aulemahal]

I think this was closed by #563. The latest cf-xarray (v0.10.4) should work with the latest xarray!.

[dcherian]

Yes, sorry about that! That particular one was a useless import, but there are others that needed to be fixed.w