keras/src/trainers/data_adapters/array_slicing.py/ScipySparseSliceable/__init__
class ScipySparseSliceable:    def __init__(self, array):
        # The COO representation is not indexable / sliceable and does not lend
        # itself to it. Use the CSR representation instead, which is sliceable.
        super().__init__(array.tocsr())