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.. _whatsnew_0210:
v0.21.0 (???)
-------------
This is a major release from 0.20.x and includes a number of API changes, deprecations, new features,
enhancements, and performance improvements along with a large number of bug fixes. We recommend that all
users upgrade to this version.
Highlights include:
Check the :ref:`API Changes <whatsnew_0210.api_breaking>` and :ref:`deprecations <whatsnew_0210.deprecations>` before updating.
.. contents:: What's new in v0.21.0
:local:
:backlinks: none
.. _whatsnew_0210.enhancements:
New features
~~~~~~~~~~~~
- Support for `PEP 519 -- Adding a file system path protocol
<https://www.python.org/dev/peps/pep-0519/>`_ on most readers and writers (:issue:`13823`)
- Added ``__fspath__`` method to :class:`~pandas.HDFStore`, :class:`~pandas.ExcelFile`,
and :class:`~pandas.ExcelWriter` to work properly with the file system path protocol (:issue:`13823`)
.. _whatsnew_0210.enhancements.other:
Other Enhancements
^^^^^^^^^^^^^^^^^^
- The ``validate`` argument for :func:`merge` function now checks whether a merge is one-to-one, one-to-many, many-to-one, or many-to-many. If a merge is found to not be an example of specified merge type, an exception of type ``MergeError`` will be raised. For more, see :ref:`here <merging.validation>` (:issue:`16270`)
- ``Series.to_dict()`` and ``DataFrame.to_dict()`` now support an ``into`` keyword which allows you to specify the ``collections.Mapping`` subclass that you would like returned. The default is ``dict``, which is backwards compatible. (:issue:`16122`)
- ``RangeIndex.append`` now returns a ``RangeIndex`` object when possible (:issue:`16212`)
- ``Series.rename_axis()`` and ``DataFrame.rename_axis()`` with ``inplace=True`` now return ``None`` while renaming the axis inplace. (:issue:`15704`)
- :func:`to_pickle` has gained a ``protocol`` parameter (:issue:`16252`). By default, this parameter is set to `HIGHEST_PROTOCOL <https://docs.python.org/3/library/pickle.html#data-stream-format>`__
- :func:`api.types.infer_dtype` now infers decimals. (:issue:`15690`)
- :func:`read_feather` has gained the ``nthreads`` parameter for multi-threaded operations (:issue:`16359`)
- :func:`DataFrame.clip()` and :func:`Series.clip()` have gained an ``inplace`` argument. (:issue:`15388`)
- :func:`crosstab` has gained a ``margins_name`` parameter to define the name of the row / column that will contain the totals when ``margins=True``. (:issue:`15972`)
- :func:`Dataframe.select_dtypes` now accepts scalar values for include/exclude as well as list-like. (:issue:`16855`)
.. _whatsnew_0210.api_breaking:
Backwards incompatible API changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Improved error handling during item assignment in pd.eval
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. _whatsnew_0210.api_breaking.pandas_eval:
:func:`eval` will now raise a ``ValueError`` when item assignment malfunctions, or
inplace operations are specified, but there is no item assignment in the expression (:issue:`16732`)
.. ipython:: python
arr = np.array([1, 2, 3])
Previously, if you attempted the following expression, you would get a not very helpful error message:
.. code-block:: ipython
In [3]: pd.eval("a = 1 + 2", target=arr, inplace=True)
...
IndexError: only integers, slices (`:`), ellipsis (`...`), numpy.newaxis (`None`)
and integer or boolean arrays are valid indices
This is a very long way of saying numpy arrays don't support string-item indexing. With this
change, the error message is now this:
.. code-block:: python
In [3]: pd.eval("a = 1 + 2", target=arr, inplace=True)
...
ValueError: Cannot assign expression output to target
It also used to be possible to evaluate expressions inplace, even if there was no item assignment:
.. code-block:: ipython
In [4]: pd.eval("1 + 2", target=arr, inplace=True)
Out[4]: 3
However, this input does not make much sense because the output is not being assigned to
the target. Now, a ``ValueError`` will be raised when such an input is passed in:
.. code-block:: ipython
In [4]: pd.eval("1 + 2", target=arr, inplace=True)
...
ValueError: Cannot operate inplace if there is no assignment
- Support has been dropped for Python 3.4 (:issue:`15251`)
- The Categorical constructor no longer accepts a scalar for the ``categories`` keyword. (:issue:`16022`)
- Accessing a non-existent attribute on a closed :class:`HDFStore` will now
raise an ``AttributeError`` rather than a ``ClosedFileError`` (:issue:`16301`)
- :func:`read_csv` now treats ``'null'`` strings as missing values by default (:issue:`16471`)
- :func:`read_csv` now treats ``'n/a'`` strings as missing values by default (:issue:`16078`)
- :class:`pandas.HDFStore`'s string representation is now faster and less detailed. For the previous behavior, use ``pandas.HDFStore.info()``. (:issue:`16503`).
- Compression defaults in HDF stores now follow pytable standards. Default is no compression and if ``complib`` is missing and ``complevel`` > 0 ``zlib`` is used (:issue:`15943`)
- ``Index.get_indexer_non_unique()`` now returns a ndarray indexer rather than an ``Index``; this is consistent with ``Index.get_indexer()`` (:issue:`16819`)
.. _whatsnew_0210.api:
Other API Changes
^^^^^^^^^^^^^^^^^
- Moved definition of ``MergeError`` to the ``pandas.errors`` module.
.. _whatsnew_0210.deprecations:
Deprecations
~~~~~~~~~~~~
- :func:`read_excel()` has deprecated ``sheetname`` in favor of ``sheet_name`` for consistency with ``.to_excel()`` (:issue:`10559`).
.. _whatsnew_0210.prior_deprecations:
Removal of prior version deprecations/changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- :func:`read_excel()` has dropped the ``has_index_names`` parameter (:issue:`10967`)
- The ``pd.options.display.mpl_style`` configuration has been dropped (:issue:`12190`)
- ``Index`` has dropped the ``.sym_diff()`` method in favor of ``.symmetric_difference()`` (:issue:`12591`)
- ``Categorical`` has dropped the ``.order()`` and ``.sort()`` methods in favor of ``.sort_values()`` (:issue:`12882`)
- :func:`eval` and :method:`DataFrame.eval` have changed the default of ``inplace`` from ``None`` to ``False`` (:issue:`11149`)
- The function ``get_offset_name`` has been dropped in favor of the ``.freqstr`` attribute for an offset (:issue:`11834`)
.. _whatsnew_0210.performance:
Performance Improvements
~~~~~~~~~~~~~~~~~~~~~~~~
.. _whatsnew_0210.bug_fixes:
Bug Fixes
~~~~~~~~~
- Fixes regression in 0.20, :func:`Series.aggregate` and :func:`DataFrame.aggregate` allow dictionaries as return values again (:issue:`16741`)
Conversion
^^^^^^^^^^
Indexing
^^^^^^^^
- When called with a null slice (e.g. ``df.iloc[:]``), the ``.iloc`` and ``.loc`` indexers return a shallow copy of the original object. Previously they returned the original object. (:issue:`13873`).
- When called on an unsorted ``MultiIndex``, the ``loc`` indexer now will raise ``UnsortedIndexError`` only if proper slicing is used on non-sorted levels (:issue:`16734`).
I/O
^^^
- Bug in :func:`read_csv` in which non integer values for the header argument generated an unhelpful / unrelated error message (:issue:`16338`)
Plotting
^^^^^^^^
Groupby/Resample/Rolling
^^^^^^^^^^^^^^^^^^^^^^^^
- Bug in ``DataFrame.resample().size()`` where an empty ``DataFrame`` did not return a ``Series`` (:issue:`14962`)
- Bug in ``infer_freq`` causing indices with 2-day gaps during the working week to be wrongly inferred as business daily (:issue:`16624`)
- Bug in ``.rolling.quantile()`` which incorrectly used different defaults than :func:`Series.quantile()` and :func:`DataFrame.quantile()` (:issue:`9413`, :issue:`16211`)
Sparse
^^^^^^
Reshaping
^^^^^^^^^
Numeric
^^^^^^^
- Bug in ``.clip()`` with ``axis=1`` and a list-like for ``threshold`` is passed; previously this raised ``ValueError`` (:issue:`15390`)
Categorical
^^^^^^^^^^^
- Bug in ``:func:Series.isin()`` when called with a categorical (:issue`16639`)
Other
^^^^^
- Bug in :func:`eval` where the ``inplace`` parameter was being incorrectly handled (:issue:`16732`)