Bug: KeyError rather than TypeError in LocStream for python >=3.12

[billsacks]

Discussed in https://github.com/orgs/esmf-org/discussions/313

^{Originally posted by xylar October 27, 2024}

Requirements

• Reviewed ESMPy Documentation
• Searched GitHub Discussions

Affiliation(s)

LANL

ESMF Version

v8.7.0 (and earlier)

Issue

I'm trying to build ESMPy 8.7.0 on conda-forge:
conda-forge/esmpy-feedstock#85
In the tests, I am seeing a KeyError:

___________________________ TestLocStream.test_slice ___________________________

self = <esmpy.test.test_api.test_locstream.TestLocStream testMethod=test_slice>

    @pytest.mark.skipif(pet_count()!=1, reason="test must be run in serial")
    def test_slice(self):
        locstream = LocStream(5, name="Test LocStream")
    
>       locstream2 = locstream[0:2]

src/esmpy/test/test_api/test_locstream.py:95: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = LocStream:
    name = 'Test LocStream' 
    lower_bounds = array([0], dtype=int32) 
    upper_bounds = array([5], dtype=int32) 
    keys = dict_items([]) 

slc = slice(0, 2, None)

    def __getitem__(self, slc):
        # initialize slc_ls
        slc_ls = slc
    
        # check that this is actually a slicing operation and not just regular item retrieval
        if not isinstance(slc, str):
            # parallel slicing is not yet enabled (collective operation)
            if pet_count() > 1:
                raise SerialMethod
            # re-initialize slc_ls
            slc_ls = get_formatted_slice(slc, self.rank)
    
        # slice at will
        try:
>           ret = super(LocStream, self).__getitem__(slc_ls)
E           KeyError: slice(0, 2, None)

src/esmpy/api/locstream.py:130: KeyError

The cause of this is that slice() objects are hashable in Python >=3.12, whereas they were not in Python <3.12, and raised a TypeError. I believe the fix would be to change the try/catch to:

       # slice at will
       if not isinstance(slc_ls, slice):
           ret = super(LocStream, self).__getitem__(slc_ls)
       else:
           # as of Python 3.12, slice objects are hashable so don't
           # raise a TypeError
           ret = self.copy()
...

This at least seems to have allowed all tests to pass.

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