BUG: clearer HDFStore error for min_itemsize on MultiIndex columns (GH-12154)#65602
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jbrockmendel wants to merge 2 commits into
Open
BUG: clearer HDFStore error for min_itemsize on MultiIndex columns (GH-12154)#65602jbrockmendel wants to merge 2 commits into
jbrockmendel wants to merge 2 commits into
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…H#12154)
Per-column min_itemsize is unsupported with MultiIndex columns because
data_columns themselves are unsupported on that axis. Previously the
user hit one of two opaque errors ("not an axis or data_column" for a
level-0 key, "cannot have non-object label DataIndexableCol" for a tuple
key). Surface the actual constraint up front in validate_data_columns
and point users at the min_itemsize={'values': N} workaround.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
min_itemsizeis fundamentally unsupported for DataFrames withMultiIndexcolumns becausedata_columnsare unsupported on that axis. Today the constraint is hit accidentally and emits one of two opaque errors:min_itemsize={1: 20}→"min_itemsize has the key [1] which is not an axis or data_column"min_itemsize={(1, 'a'): 20}→"cannot have non-object label DataIndexableCol"validate_data_columnsand point users at the workingmin_itemsize={'values': N}form.closes #12154
Test plan
test_append_min_itemsize_multiindex_columnscovering the level-0-key form, the tuple-key form, and the'values'round-trip.pandas/tests/io/pytables/test_append.pypasses locally.🤖 Generated with Claude Code