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Fix nightly with pd.DataFrame.rename calling for MultiIndex.fillna #1449

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Oct 25, 2025
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Fix nightly with pd.DataFrame.rename calling for MultiIndex.fillna #1449

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Fix nightly with pd.DataFrame.rename calling for MultiIndex.fillna
loicdiridollou Oct 24, 2025
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loicdiridollou Oct 24, 2025
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7 changes: 6 additions & 1 deletion tests/test_frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2550,11 +2550,16 @@ def test_types_rename() -> None:
# Apparently all of these calls are accepted by pandas
check(assert_type(df.rename(columns={None: "b"}), pd.DataFrame), pd.DataFrame)
check(assert_type(df.rename(columns={"": "b"}), pd.DataFrame), pd.DataFrame)
check(assert_type(df.rename(columns={(2, 1): "b"}), pd.DataFrame), pd.DataFrame)
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Could you change the stub files and invalidate this usage?

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That would actually break, the issue is at run time when you try to rename a dataframe with an Index when the mapper is designed for a multiindex. Since we do not have the capacity to differenciate 'dataframe with index' and 'dataframe with multiindex' you can't force that behavior in the stubs. Do you see what I mean?

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One possible solution would be to only allow rename(column=d), where d is a dictionary containing tuples as keys and values of equal length, so that columns={(2, 1): "b"} will be forbidden.

However I couldn't work out how to implement this. For now, I'll leave it as it is.

check(
assert_type(df.rename(columns=lambda s: s.upper()), pd.DataFrame), pd.DataFrame
)

df_multiindex = pd.DataFrame(columns=[("a", 1), ("a", 2)])
check(
assert_type(df_multiindex.rename(columns={(1, 2): ("b", "a")}), pd.DataFrame),
pd.DataFrame,
)


def test_types_rename_axis() -> None:
df = pd.DataFrame({"col_name": [1, 2, 3]})
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