.. _whatsnew_230:

What's new in 2.3.0 (June 4, 2025)
------------------------------------

These are the changes in pandas 2.3.0. See :ref:`release` for a full changelog
including other versions of pandas.

{{ header }}

.. ---------------------------------------------------------------------------

.. _whatsnew_230.upcoming_changes:

Upcoming changes in pandas 3.0
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

pandas 3.0 will bring two bigger changes to the default behavior of pandas.

Dedicated string data type by default
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Historically, pandas represented string columns with NumPy ``object`` data type.
This representation has numerous problems: it is not specific to strings (any
Python object can be stored in an ``object``-dtype array, not just strings) and
it is often not very efficient (both performance wise and for memory usage).

Starting with the upcoming pandas 3.0 release, a dedicated string data type will
be enabled by default (backed by PyArrow under the hood, if installed, otherwise
falling back to NumPy). This means that pandas will start inferring columns
containing string data as the new ``str`` data type when creating pandas
objects, such as in constructors or IO functions.

Old behavior:

.. code-block:: python

    >>> ser = pd.Series(["a", "b"])
    0    a
    1    b
    dtype: object

New behavior:

.. code-block:: python

    >>> ser = pd.Series(["a", "b"])
    0    a
    1    b
    dtype: str

The string data type that is used in these scenarios will mostly behave as NumPy
object would, including missing value semantics and general operations on these
columns.

However, the introduction of a new default dtype will also have some breaking
consequences to your code (for example when checking for the ``.dtype`` being
object dtype). To allow testing it in advance of the pandas 3.0 release, this
future dtype inference logic can be enabled in pandas 2.3 with:

.. code-block:: python

   pd.options.future.infer_string = True

See the :ref:`string_migration_guide` for more details on the behaviour changes
and how to adapt your code to the new default.

Copy-on-Write
^^^^^^^^^^^^^

The currently optional mode Copy-on-Write will be enabled by default in pandas 3.0. There
won't be an option to retain the legacy behavior.

In summary, the new "copy-on-write" behaviour will bring changes in behavior in
how pandas operates with respect to copies and views.

1. The result of *any* indexing operation (subsetting a DataFrame or Series in any way,
   i.e. including accessing a DataFrame column as a Series) or any method returning a
   new DataFrame or Series, always *behaves as if* it were a copy in terms of user
   API.
2. As a consequence, if you want to modify an object (DataFrame or Series), the only way
   to do this is to directly modify that object itself.

Because every single indexing step now behaves as a copy, this also means that
"chained assignment" (updating a DataFrame with multiple setitem steps) will
stop working. Because this now consistently never works, the
``SettingWithCopyWarning`` will be removed.

The new behavioral semantics are explained in more detail in the
:ref:`user guide about Copy-on-Write <copy_on_write>`.

The new behavior can be enabled since pandas 2.0 with the following option:

.. code-block:: python

   pd.options.mode.copy_on_write = True

Some of the behaviour changes allow a clear deprecation, like the changes in
chained assignment. Other changes are more subtle and thus, the warnings are
hidden behind an option that can be enabled since pandas 2.2:

.. code-block:: python

   pd.options.mode.copy_on_write = "warn"

This mode will warn in many different scenarios that aren't actually relevant to
most queries. We recommend exploring this mode, but it is not necessary to get rid
of all of these warnings. The :ref:`migration guide <copy_on_write.migration_guide>`
explains the upgrade process in more detail.

.. _whatsnew_230.enhancements:

Enhancements
~~~~~~~~~~~~

.. _whatsnew_230.enhancements.other:

Other enhancements
^^^^^^^^^^^^^^^^^^

- The semantics for the ``copy`` keyword in ``__array__`` methods (i.e. called
  when using ``np.array()`` or ``np.asarray()`` on pandas objects) has been
  updated to work correctly with NumPy >= 2 (:issue:`57739`)
- :meth:`Series.str.decode` result now has :class:`StringDtype` when ``future.infer_string`` is True (:issue:`60709`)
- :meth:`~Series.to_hdf` and :meth:`~DataFrame.to_hdf` now round-trip with :class:`StringDtype`  (:issue:`60663`)
- Improved ``repr`` of :class:`.NumpyExtensionArray` to account for NEP51 (:issue:`61085`)
- The :meth:`Series.str.decode` has gained the argument ``dtype`` to control the dtype of the result (:issue:`60940`)
- The :meth:`~Series.cumsum`, :meth:`~Series.cummin`, and :meth:`~Series.cummax` reductions are now implemented for :class:`StringDtype` columns (:issue:`60633`)
- The :meth:`~Series.sum` reduction is now implemented for :class:`StringDtype` columns (:issue:`59853`)

.. ---------------------------------------------------------------------------
.. _whatsnew_230.deprecations:

Deprecations
~~~~~~~~~~~~
- Deprecated allowing non-``bool`` values for ``na`` in :meth:`.str.contains`, :meth:`.str.startswith`, and :meth:`.str.endswith` for dtypes that do not already disallow these (:issue:`59615`)
- Deprecated the ``"pyarrow_numpy"`` storage option for :class:`StringDtype` (:issue:`60152`)
- The deprecation of setting the argument ``include_groups`` to ``True`` in :meth:`DataFrameGroupBy.apply` has been promoted from a ``DeprecationWarning`` to ``FutureWarning``; only ``False`` will be allowed (:issue:`7155`)

.. ---------------------------------------------------------------------------
.. _whatsnew_230.bug_fixes:

Bug fixes
~~~~~~~~~

Numeric
^^^^^^^
- Bug in :meth:`Series.mode` and :meth:`DataFrame.mode` with ``dropna=False`` where not all dtypes would sort in the presence of ``NA`` values (:issue:`60702`)
- Bug in :meth:`Series.round` where a ``TypeError`` would always raise with ``object`` dtype (:issue:`61206`)

Strings
^^^^^^^
- Bug in :meth:`Series.__pos__` and :meth:`DataFrame.__pos__` where an ``Exception`` was not raised for :class:`StringDtype` with ``storage="pyarrow"`` (:issue:`60710`)
- Bug in :meth:`Series.rank` for :class:`StringDtype` with ``storage="pyarrow"`` that incorrectly returned integer results with ``method="average"`` and raised an error if it would truncate results (:issue:`59768`)
- Bug in :meth:`Series.replace` with :class:`StringDtype` when replacing with a non-string value was not upcasting to ``object`` dtype (:issue:`60282`)
- Bug in :meth:`Series.str.center` with :class:`StringDtype` with ``storage="pyarrow"`` not matching the python behavior in corner cases with an odd number of fill characters (:issue:`54792`)
- Bug in :meth:`Series.str.replace` when ``n < 0`` for :class:`StringDtype` with ``storage="pyarrow"`` (:issue:`59628`)
- Bug in :meth:`Series.str.slice` with negative ``step`` with :class:`ArrowDtype` and :class:`StringDtype` with ``storage="pyarrow"`` giving incorrect results (:issue:`59710`)

Indexing
^^^^^^^^
- Bug in :meth:`Index.get_indexer` round-tripping through string dtype when ``infer_string`` is enabled (:issue:`55834`)

I/O
^^^
- Bug in :meth:`DataFrame.to_excel` which stored decimals as strings instead of numbers (:issue:`49598`)

Other
^^^^^
- Fixed usage of ``inspect`` when the optional dependencies ``pyarrow`` or ``jinja2``
  are not installed (:issue:`60196`)
-

.. ---------------------------------------------------------------------------
.. _whatsnew_230.contributors:

Contributors
~~~~~~~~~~~~

.. contributors:: v2.2.3..v2.3.0
