# 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 (GH39695)

- Fixed regression in nullable integer unary ops propagating mask on assignment (GH39943)

- Fixed regression in `DataFrame.__setitem__()` not aligning `DataFrame` on right-hand side for boolean indexer (GH39931)

- 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 (GH39985)

- 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) (GH39434)

- 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 (GH40018)

## Contributors

For contributors, please see /usr/share/doc/contributors_list.txt or https://github.com/pandas-dev/pandas/graphs/contributors