BUG : Fix Excel header NaN duplication with merged MultiIndex columns in to_excel #62576
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justine202429 force-pushed the bugfix-Issue62340 branch from 6703b44 to a5784f5 Compare 
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Alvaro-Kothe suggested changes Oct 19, 2025
Comment on lines +1597 to +1600
| with ExcelWriter("test.xlsx", engine="openpyxl") as writer: | ||
| df.to_excel(writer, sheet_name="Sheet1", merge_cells=merge_cells) | ||
| | ||
| reader = ExcelFile("test.xlsx") |
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Don't read and write to CWD, either use a temporary file, or use an in-memory buffer.
| DummyClass.assert_called_and_reset() | ||
| | ||
| @td.skip_if_no("openpyxl") | ||
| def test_to_excel_multiindex_nan_in_columns(self, merge_cells): |
Comment on lines +1601 to +1605
| result = pd.read_excel(reader, index_col=0, header=[0, 1]) | ||
| | ||
| original_values = df.to_numpy() | ||
| result_values = result.to_numpy() | ||
| tm.assert_numpy_array_equal(original_values, result_values) |
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Create an expected DataFrame and use tm.assert_frame_equal
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doc/source/whatsnew/vX.X.X.rstfile if fixing a bug or adding a new feature.