# 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 (GH43183)

- Fixed regression in `GroupBy.agg()` where it was failing silently with mixed data types along `axis=1` and `MultiIndex` (GH43209)

- Fixed regression in `merge()` with integer and `NaN` keys failing with `outer` merge (GH43550)

- Fixed regression in `DataFrame.corr()` raising `ValueError` with `method="spearman"` on 32-bit platforms (GH43588)

- Fixed performance regression in `MultiIndex.equals()` (GH43549)

- Fixed performance regression in `GroupBy.first()` and `GroupBy.last()` with `StringDtype` (GH41596)

- Fixed regression in `Series.cat.reorder_categories()` failing to update the categories on the `Series` (GH43232)

- Fixed regression in `Series.cat.categories()` setter failing to update the categories on the `Series` (GH43334)

- Fixed regression in `read_csv()` raising `UnicodeDecodeError` exception when `memory_map=True` (GH43540)

- Fixed regression in `DataFrame.explode()` raising `AssertionError` when `column` is any scalar which is not a string (GH43314)

- Fixed regression in `Series.aggregate()` attempting to pass `args` and `kwargs` multiple times to the user supplied `func` in certain cases (GH43357)

- 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 (GH43386)

- Fixed regression in `DataFrame.groupby.rolling.cov()` and `DataFrame.groupby.rolling.corr()` computing incorrect results if the input groupings were not sorted (GH43386)

## Bug fixes

- Fixed bug in `pandas.DataFrame.groupby.rolling()` and `pandas.api.indexers.FixedForwardWindowIndexer` leading to segfaults and window endpoints being mixed across groups (GH43267)

- Fixed bug in `GroupBy.mean()` with datetimelike values including `NaT` values returning incorrect results (GH43132)

- Fixed bug in `Series.aggregate()` not passing the first `args` to the user supplied `func` in certain cases (GH43357)

- Fixed memory leaks in `Series.rolling.quantile()` and `Series.rolling.median()` (GH43339)

## Other

- The minimum version of Cython needed to compile pandas is now `0.29.24` (GH43729)

## Contributors

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