Fix at/iat indexers to reject list-like keys
#21213
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Resolves rapidsai#20561 In pandas, .at and .iat are scalar-only indexers that reject list-like inputs, unlike .loc and .iloc which accept broader indexing. cuDF was incorrectly allowing list-like indexers for at/iat. Changes: - Add validate_scalar_key() function in indexing_utils.py that validates keys contain only scalar values - Update _SeriesAtIndexer and _SeriesiAtIndexer to validate keys - Update _DataFrameAtIndexer and _DataFrameiAtIndexer to validate keys - Add comprehensive test coverage for at/iat validation Error messages match pandas where possible: - .at raises ValueError with "Invalid call for scalar access" - .iat raises ValueError with "iAt based indexing can only have integer indexers" Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
galipremsagar
approved these changes
Jan 28, 2026
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Description
Closes #20561
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