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# What’s new in 2.3.1 (July 7, 2025)

These are the changes in pandas 2.3.1. See Release notes for a full changelog including other versions of pandas.

## Improvements and fixes for the StringDtype

Most changes in this release are related to `StringDtype` which will become the default string dtype in pandas 3.0. See Upcoming changes in pandas 3.0 for more details.

### Comparisons between different string dtypes

In previous versions, comparing `Series` of different string dtypes (e.g. `pd.StringDtype("pyarrow", na_value=pd.NA)` against `pd.StringDtype("python", na_value=np.nan)`) would result in inconsistent resulting dtype or incorrectly raise (GH 60639). pandas will now use the hierarchy

> object < (python, NaN) < (pyarrow, NaN) < (python, NA) < (pyarrow, NA)

in determining the result dtype when there are different string dtypes compared. Some examples:

- When `pd.StringDtype("pyarrow", na_value=pd.NA)` is compared against any other string dtype, the result will always be `boolean[pyarrow]`.

- When `pd.StringDtype("python", na_value=pd.NA)` is compared against `pd.StringDtype("pyarrow", na_value=np.nan)`, the result will be `boolean`, the NumPy-backed nullable extension array.

- When `pd.StringDtype("python", na_value=pd.NA)` is compared against `pd.StringDtype("python", na_value=np.nan)`, the result will be `boolean`, the NumPy-backed nullable extension array.

### Index set operations ignore empty RangeIndex and object dtype Index

When enabling the `future.infer_string` option, `Index` set operations (like union or intersection) will now ignore the dtype of an empty `RangeIndex` or empty `Index` with `object` dtype when determining the dtype of the resulting Index (GH 60797).

This ensures that combining such empty Index with strings will infer the string dtype correctly, rather than defaulting to `object` dtype. For example:

    >>> pd.options.future.infer_string = True
    >>> df = pd.DataFrame()
    >>> df.columns.dtype
    dtype('int64')               # default RangeIndex for empty columns
    >>> df["a"] = [1, 2, 3]
    >>> df.columns.dtype
    <StringDtype(na_value=nan)>  # new columns use string dtype instead of object dtype

### Bug fixes

- Bug in `DataFrameGroupBy.min()`, `DataFrameGroupBy.max()`, `Resampler.min()`, `Resampler.max()` where all NA values of string dtype would return float instead of string dtype (GH 60810)

- Bug in `DataFrame.join()` incorrectly downcasting object-dtype indexes (GH 61771)

- Bug in `DataFrame.sum()` with `axis=1`, `DataFrameGroupBy.sum()` or `SeriesGroupBy.sum()` with `skipna=True`, and `Resampler.sum()` with all NA values of `StringDtype` resulted in `0` instead of the empty string `""` (GH 60229)

- Fixed bug in `DataFrame.explode()` and `Series.explode()` where methods would fail with `dtype="str"` (GH 61623)

- Fixed bug in unpickling objects pickled in pandas versions pre-2.3.0 that used `StringDtype` (GH 61763)

## Contributors

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