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# What’s new in 1.2.3 (March 02, 2021)

These are the changes in pandas 1.2.3. See Release notes for a full changelog including other versions of pandas.

## Fixed regressions

- Fixed regression in `to_excel()` raising `KeyError` when giving duplicate columns with `columns` attribute (GH 39695)

- Fixed regression in nullable integer unary ops propagating mask on assignment (GH 39943)

- Fixed regression in `DataFrame.__setitem__()` not aligning `DataFrame` on right-hand side for boolean indexer (GH 39931)

- Fixed regression in `to_json()` failing to use `compression` with URL-like paths that are internally opened in binary mode or with user-provided file objects that are opened in binary mode (GH 39985)

- Fixed regression in `Series.sort_index()` and `DataFrame.sort_index()`, which exited with an ungraceful error when having kwarg `ascending=None` passed. Passing `ascending=None` is still considered invalid, and the improved error message suggests a proper usage (`ascending` must be a boolean or a list-like of boolean) (GH 39434)

- Fixed regression in `DataFrame.transform()` and `Series.transform()` giving incorrect column labels when passed a dictionary with a mix of list and non-list values (GH 40018)

## Contributors

A total of 14 people contributed patches to this release. People with a “+” by their names contributed a patch for the first time.

- Daniel Saxton

- Dylan Percy +

- Jody Klymak +

- Maxim Ivanov

- MeeseeksMachine

- Pandas Development Team

- Richard Shadrach

- Rohit Gupta +

- Simon Hawkins

- Torsten Wörtwein

- jbrockmendel

- morrme +

- partev

- patrick