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# What’s new in 1.3.4 (October 17, 2021)

These are the changes in pandas 1.3.4. See Release notes for a full changelog including other versions of pandas.

## Fixed regressions

- Fixed regression in `DataFrame.convert_dtypes()` incorrectly converts byte strings to strings (GH 43183)

- Fixed regression in `DataFrameGroupBy.agg()` and `SeriesGroupBy.agg()` were failing silently with mixed data types along `axis=1` and `MultiIndex` (GH 43209)

- Fixed regression in `merge()` with integer and `NaN` keys failing with `outer` merge (GH 43550)

- Fixed regression in `DataFrame.corr()` raising `ValueError` with `method="spearman"` on 32-bit platforms (GH 43588)

- Fixed performance regression in `MultiIndex.equals()` (GH 43549)

- Fixed performance regression in `DataFrameGroupBy.first()`, `SeriesGroupBy.first()`, `DataFrameGroupBy.last()`, and `SeriesGroupBy.last()` with `StringDtype` (GH 41596)

- Fixed regression in `Series.cat.reorder_categories()` failing to update the categories on the `Series` (GH 43232)

- Fixed regression in `Series.cat.categories()` setter failing to update the categories on the `Series` (GH 43334)

- Fixed regression in `read_csv()` raising `UnicodeDecodeError` exception when `memory_map=True` (GH 43540)

- Fixed regression in `DataFrame.explode()` raising `AssertionError` when `column` is any scalar which is not a string (GH 43314)

- Fixed regression in `Series.aggregate()` attempting to pass `args` and `kwargs` multiple times to the user supplied `func` in certain cases (GH 43357)

- Fixed regression when iterating over a `DataFrame.groupby.rolling` object causing the resulting DataFrames to have an incorrect index if the input groupings were not sorted (GH 43386)

- Fixed regression in `DataFrame.groupby.rolling.cov()` and `DataFrame.groupby.rolling.corr()` computing incorrect results if the input groupings were not sorted (GH 43386)

## Bug fixes

- Fixed bug in `pandas.DataFrame.groupby.rolling()` and `pandas.api.indexers.FixedForwardWindowIndexer` leading to segfaults and window endpoints being mixed across groups (GH 43267)

- Fixed bug in `DataFrameGroupBy.mean()` and `SeriesGroupBy.mean()` with datetimelike values including `NaT` values returning incorrect results (GH 43132)

- Fixed bug in `Series.aggregate()` not passing the first `args` to the user supplied `func` in certain cases (GH 43357)

- Fixed memory leaks in `Series.rolling.quantile()` and `Series.rolling.median()` (GH 43339)

## Other

- The minimum version of Cython needed to compile pandas is now `0.29.24` (GH 43729)

## Contributors

A total of 17 people contributed patches to this release. People with a “+” by their names contributed a patch for the first time.

- Alexey Györi +

- DSM

- Irv Lustig

- Jeff Reback

- Julien de la Bruère-T +

- Matthew Zeitlin

- MeeseeksMachine

- Pandas Development Team

- Patrick Hoefler

- Richard Shadrach

- Shoham Debnath

- Simon Hawkins

- Thomas Li

- aptalca +

- jbrockmendel

- michal-gh +

- realead