Fix syntax error in test related to cupy

[hmaarrfk]

I suspect the CIs don't have cupy which meant that this line didn't get hit.

Recreation:

mamba create --name xr_py10 python=3.10 --channel conda-forge --override-channels
mamba activate xr_py10
pip install -e . -vv
pip install pytest
mamba install cupy

pytest xarray/tests/test_array_api.py -x

Fails on my machine.

Happy to provide more info.

See: https://github.com/pydata/xarray/pull/8723/files#r1590298540

• Closes #xxxx
• Tests added
• User visible changes (including notable bug fixes) are documented in whats-new.rst
• New functions/methods are listed in api.rst

[max-sixty]

Nice, thanks!

(good reminder that type checking is useful!)

[keewis]

this is actually valid syntax... except := has a very low priority, which means that we're trying to assign array_type("cupy") and any(...) to array_type_cupy, which does not work because we're making use of it in the generator expression. It would work, however, if we wrapped the := in parentheses:

    elif (array_type_cupy := array_type("cupy")) and any(  # noqa: F841
        isinstance(x, array_type_cupy) for x in scalars_or_arrays  # noqa: F821
    ):

[hmaarrfk]

hmm i see, yeah, I've never used the walrus operator in practice. only read about it.