BUG: DataFrame.loc setitem with list-like value on single-column EA DataFrame#65241
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mroeschke merged 2 commits intopandas-dev:mainfrom Apr 21, 2026
Merged
BUG: DataFrame.loc setitem with list-like value on single-column EA DataFrame#65241mroeschke merged 2 commits intopandas-dev:mainfrom
mroeschke merged 2 commits intopandas-dev:mainfrom
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…ataFrame (pandas-dev#44103) Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
mroeschke
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Apr 20, 2026
| def test_loc_setitem_single_column_listlike_value(self): | ||
| # GH#44103 | ||
| df = DataFrame({"a": [None, "two"]}, index=[0, 1], dtype="string") | ||
| df.loc[0, ["a"]] = ["one"] |
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Do we have tests with assignment across multiple columns e.g. ["a", "b"]] = ["1", "2"]?
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updated with a new test
mroeschke
reviewed
Apr 20, 2026
| and len(indexer) == 2 | ||
| and is_integer(indexer[0]) | ||
| and not is_integer(indexer[1]) | ||
| and is_list_like(value) |
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Do we need to check that len(values) == len(indexer) - 1?
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i think that is already handled within the split path
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Thanks @jbrockmendel |
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…h-origin * upstream/main: (31 commits) DOC:Missing r in your (pandas-dev#65323) DOC: fix grammar in the .dt accessor section (pandas-dev#65325) REGR: restore rank() for ExtensionArrays with custom values for sorting (pandas-dev#64976) BUG: MultiIndex.get_loc returns scalar for unique key in non-unique index (pandas-dev#65234) BUG/TST: add test for _cast_pointwise_result robustness + fix some cases (pandas-dev#65318) BUG: fix .loc with tuple key on MultiIndex with IntervalIndex level (pandas-dev#65239) BUG: permit building from source with mingw (pandas-dev#64849) BUG: DataFrame.loc setitem with list-like value on single-column EA DataFrame (pandas-dev#65241) PERF: preserve block memory layout in Block.copy (GH#60469) (pandas-dev#65302) PERF: short-circuit sort_index(level=...) on monotonic non-MultiIndex (pandas-dev#65279) BUG: fix FloatingArray.astype(str) crash with distinguish_nan_and_na=True (pandas-dev#65038) BUG: fix to_timedelta ignoring unit for mixed round/non-round floats (pandas-dev#65170) BUG: DataFrame.loc preserves original index name when key is an Index (pandas-dev#65229) REF: continue moving freq management off DatetimeArray/TimedeltaArray (GH#24566) (pandas-dev#65285) REF: remove redundant BaseMaskedArray.map override (pandas-dev#65297) Bump github/codeql-action from 4.35.1 to 4.35.2 (pandas-dev#65310) Bump actions/setup-node from 6.3.0 to 6.4.0 (pandas-dev#65309) BUG: Fix formatters applied to wrong columns in truncated DataFrame.to_string (GH#35410) (pandas-dev#65288) PERF: optimize block consolidation (pandas-dev#64574) CLN: Replace no_default signature with False for allow_duplicates in insert and reset_index (pandas-dev#65146) ...
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Summary
df.loc[row, [col]] = [val]raisingValueErroron single-column DataFrames with ExtensionArray dtypes (e.g.string,Int64)_setitem_single_blocknow processes column-by-column when the indexer selects a scalar row and array-like columns with a list-like value, matching the split-path behaviorcloses #44103
Test plan
test_loc_setitem_single_column_listlike_value— sets with a plain listtest_loc_setitem_single_column_ea_value— sets with apd.array🤖 Generated with Claude Code