v0.24.0.txt

.. _whatsnew_0240:

v0.24.0
-------

.. _whatsnew_0240.enhancements:

New features
~~~~~~~~~~~~

- ``ExcelWriter`` now accepts ``mode`` as a keyword argument, enabling append to existing workbooks when using the ``openpyxl`` engine (:issue:`3441`)

.. _whatsnew_0240.enhancements.other:

.. _whatsnew_0240.enhancements.extension_array_operators

``ExtensionArray`` operator support
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

A ``Series`` based on ``ExtensionArray`` now supports arithmetic and comparison
operators.  There are two approaches for providing operator support for an ExtensionArray:

1. Define each of the operators on your ExtensionArray subclass. 
2. Use an operator implementation from pandas that depends on operators that are already defined
   on the underlying elements (scalars) of the ExtensionArray.

To use the first approach where you define your own implementation of the operators,
you define each operator such as `__add__`, __le__`, etc. on your ExtensionArray
subclass.

For the second approach, which is appropriate if your ExtensionArray contains 
elements that already have the operators
defined on a per-element basis, pandas provides a mixin,
:class:`ExtensionScalarOpsMixin` that you can use to
define the operators on your ExtensionArray subclass.
If developing an ``ExtensionArray`` subclass, for example ``MyExtensionArray``,
simply include ``ExtensionScalarOpsMixin`` as a parent class of ``MyExtensionArray``
and then call the methods :meth:`~MyExtensionArray._add_arithmetic_ops` and/or
:meth:`~MyExtensionArray._add_comparison_ops` to hook the operators into 
your ``MyExtensionArray`` class, as follows:

.. code-block:: python

    class MyExtensionArray(ExtensionArray, ExtensionScalarOpsMixin):
        pass
    
    MyExtensionArray._add_arithmetic_ops()
    MyExtensionArray._add_comparison_ops()

See the :ref:`ExtensionArray Operator Support
<extending.extension.operator>` documentation section for details on both 
ways of adding operator support.

Other Enhancements
^^^^^^^^^^^^^^^^^^
- :func:`to_datetime` now supports the ``%Z`` and ``%z`` directive when passed into ``format`` (:issue:`13486`)
- :func:`Series.mode` and :func:`DataFrame.mode` now support the ``dropna`` parameter which can be used to specify whether NaN/NaT values should be considered (:issue:`17534`)
- :func:`to_csv` now supports ``compression`` keyword when a file handle is passed. (:issue:`21227`)
- :meth:`Index.droplevel` is now implemented also for flat indexes, for compatibility with MultiIndex (:issue:`21115`)


.. _whatsnew_0240.api_breaking:


Backwards incompatible API changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. _whatsnew_0240.api.datetimelike.normalize:

Tick DateOffset Normalize Restrictions
--------------------------------------

Creating a ``Tick`` object (:class:``Day``, :class:``Hour``, :class:``Minute``,
:class:``Second``, :class:``Milli``, :class:``Micro``, :class:``Nano``) with
`normalize=True` is no longer supported.  This prevents unexpected behavior
where addition could fail to be monotone or associative.  (:issue:`21427`)

.. ipython:: python

    ts = pd.Timestamp('2018-06-11 18:01:14')
    ts
    tic = pd.offsets.Hour(n=2, normalize=True)
    tic

Previous Behavior:

.. code-block:: ipython

    In [4]: ts + tic
    Out [4]: Timestamp('2018-06-11 00:00:00')

    In [5]: ts + tic + tic + tic == ts + (tic + tic + tic)
    Out [5]: False

Current Behavior:

.. ipython:: python

    tic = pd.offsets.Hour(n=2)
    ts + tic + tic + tic == ts + (tic + tic + tic)


.. _whatsnew_0240.api.datetimelike:

Datetimelike API Changes
^^^^^^^^^^^^^^^^^^^^^^^^

- For :class:`DatetimeIndex` and :class:`TimedeltaIndex` with non-``None`` ``freq`` attribute, addition or subtraction of integer-dtyped array or ``Index`` will return an object of the same class (:issue:`19959`)
- :class:`DateOffset` objects are now immutable. Attempting to alter one of these will now raise ``AttributeError`` (:issue:`21341`)

.. _whatsnew_0240.api.other:

Other API Changes
^^^^^^^^^^^^^^^^^

.. _whatsnew_0240.api.other.incompatibilities:

Series and Index Data-Dtype Incompatibilities
---------------------------------------------

``Series`` and ``Index`` constructors now raise when the
data is incompatible with a passed ``dtype=`` (:issue:`15832`)

Previous Behavior:

.. code-block:: ipython

    In [4]: pd.Series([-1], dtype="uint64")
    Out [4]:
    0    18446744073709551615
    dtype: uint64

Current Behavior:

.. code-block:: ipython

    In [4]: pd.Series([-1], dtype="uint64")
    Out [4]:
    ...
    OverflowError: Trying to coerce negative values to unsigned integers

- :class:`DatetimeIndex` now accepts :class:`Int64Index` arguments as epoch timestamps (:issue:`20997`)
-
-

.. _whatsnew_0240.deprecations:

Deprecations
~~~~~~~~~~~~

- :meth:`DataFrame.to_stata`, :meth:`read_stata`, :class:`StataReader` and :class:`StataWriter` have deprecated the ``encoding`` argument.  The encoding of a Stata dta file is determined by the file type and cannot be changed (:issue:`21244`).
-
-

.. _whatsnew_0240.prior_deprecations:

Removal of prior version deprecations/changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- The ``LongPanel`` and ``WidePanel`` classes have been removed (:issue:`10892`)
-
-
-

.. _whatsnew_0240.performance:

Performance Improvements
~~~~~~~~~~~~~~~~~~~~~~~~

- Improved performance of :func:`Series.describe` in case of numeric dtpyes (:issue:`21274`)
- Improved performance of :func:`pandas.core.groupby.GroupBy.rank` when dealing with tied rankings (:issue:`21237`)
-

.. _whatsnew_0240.docs:

Documentation Changes
~~~~~~~~~~~~~~~~~~~~~

- Added sphinx spelling extension, updated documentation on how to use the spell check (:issue:`21079`)
-
-

.. _whatsnew_0240.bug_fixes:

Bug Fixes
~~~~~~~~~

Categorical
^^^^^^^^^^^

-
-
-

Datetimelike
^^^^^^^^^^^^

- Fixed bug where two :class:`DateOffset` objects with different ``normalize`` attributes could evaluate as equal (:issue:`21404`)
- Bug in :class:`Index` with ``datetime64[ns, tz]`` dtype that did not localize integer data correctly (:issue:`20964`)
-

Timedelta
^^^^^^^^^

-
-
-

Timezones
^^^^^^^^^

-
-
-

Offsets
^^^^^^^

-
-

Numeric
^^^^^^^

-
-
-

Strings
^^^^^^^

-
-
-

Indexing
^^^^^^^^

- The traceback from a ``KeyError`` when asking ``.loc`` for a single missing label is now shorter and more clear (:issue:`21557`)
-
-

MultiIndex
^^^^^^^^^^

-
-
-

I/O
^^^

-
-
-

Plotting
^^^^^^^^

-
-
-

Groupby/Resample/Rolling
^^^^^^^^^^^^^^^^^^^^^^^^

-
-
-

Sparse
^^^^^^

-
-
-

Reshaping
^^^^^^^^^

-
-
-

ExtensionArray
^^^^^^^^^^^^^^

- :meth:`Series.combine()` works correctly with :class:`~pandas.api.extensions.ExtensionArray` inside of :class:`Series` (:issue:`20825`)
- :meth:`Series.combine()` with scalar argument now works for any function type (:issue:`21248`)
-
-

Other
^^^^^

- :meth: `~pandas.io.formats.style.Styler.background_gradient` now takes a ``text_color_threshold`` parameter to automatically lighten the text color based on the luminance of the background color. This improves readability with dark background colors without the need to limit the background colormap range. (:issue:`21258`)
-
-
-