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# What’s new in 1.4.2 (April 2, 2022)

These are the changes in pandas 1.4.2. See Release notes for a full changelog including other versions of pandas.

## Fixed regressions

- Fixed regression in `DataFrame.drop()` and `Series.drop()` when `Index` had extension dtype and duplicates (GH 45860)

- Fixed regression in `read_csv()` killing python process when invalid file input was given for `engine="c"` (GH 45957)

- Fixed memory performance regression in `Series.fillna()` when called on a `DataFrame` column with `inplace=True` (GH 46149)

- Provided an alternative solution for passing custom Excel formats in `Styler.to_excel()`, which was a regression based on stricter CSS validation. Examples available in the documentation for `Styler.format()` (GH 46152)

- Fixed regression in `DataFrame.replace()` when a replacement value was also a target for replacement (GH 46306)

- Fixed regression in `DataFrame.replace()` when the replacement value was explicitly `None` when passed in a dictionary to `to_replace` (GH 45601, GH 45836)

- Fixed regression when setting values with `DataFrame.loc()` losing `MultiIndex` names if `DataFrame` was empty before (GH 46317)

- Fixed regression when rendering boolean datatype columns with `Styler()` (GH 46384)

- Fixed regression in `Groupby.rolling()` with a frequency window that would raise a `ValueError` even if the datetimes within each group were monotonic (GH 46061)

## Bug fixes

- Fix some cases for subclasses that define their `_constructor` properties as general callables (GH 46018)

- Fixed “longtable” formatting in `Styler.to_latex()` when `column_format` is given in extended format (GH 46037)

- Fixed incorrect rendering in `Styler.format()` with `hyperlinks="html"` when the url contains a colon or other special characters (GH 46389)

- Improved error message in `Rolling` when `window` is a frequency and `NaT` is in the rolling axis (GH 46087)

## Contributors

A total of 15 people contributed patches to this release. People with a “+” by their names contributed a patch for the first time.

- Daniel Schmidt

- JHM Darbyshire

- Jonas Haag

- Jordan Hicks +

- Joris Van den Bossche

- Kian Eliasi +

- Luke Manley

- Marco Edward Gorelli

- Matthew Roeschke

- MeeseeksMachine

- Pandas Development Team

- Patrick Hoefler

- Richard Shadrach

- Simon Hawkins

- jbrockmendel