.. _whatsnew_121:

What's new in 1.2.1 (January 20, 2021)
--------------------------------------

These are the changes in pandas 1.2.1. See :ref:`release` for a full changelog
including other versions of pandas.

{{ header }}

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

.. _whatsnew_121.regressions:

Fixed regressions
~~~~~~~~~~~~~~~~~
- Fixed regression in :meth:`~DataFrame.to_csv` that created corrupted zip files when there were more rows than ``chunksize`` (:issue:`38714`)
- Fixed regression in :meth:`~DataFrame.to_csv` opening ``codecs.StreamReaderWriter`` in binary mode instead of in text mode (:issue:`39247`)
- Fixed regression in :meth:`read_csv` and other read functions were the encoding error policy (``errors``) did not default to ``"replace"`` when no encoding was specified (:issue:`38989`)
- Fixed regression in :func:`read_excel` with non-rawbyte file handles (:issue:`38788`)
- Fixed regression in :meth:`DataFrame.to_stata` not removing the created file when an error occurred (:issue:`39202`)
- Fixed regression in ``DataFrame.__setitem__`` raising ``ValueError`` when expanding :class:`DataFrame` and new column is from type ``"0 - name"`` (:issue:`39010`)
- Fixed regression in setting with :meth:`DataFrame.loc`  raising ``ValueError`` when :class:`DataFrame` has unsorted :class:`MultiIndex` columns and indexer is a scalar (:issue:`38601`)
- Fixed regression in setting with :meth:`DataFrame.loc` raising ``KeyError`` with :class:`MultiIndex` and list-like columns indexer enlarging :class:`DataFrame` (:issue:`39147`)
- Fixed regression in :meth:`~DataFrame.groupby()` with :class:`Categorical` grouping column not showing unused categories for ``grouped.indices`` (:issue:`38642`)
- Fixed regression in :meth:`.DataFrameGroupBy.sem` and :meth:`.SeriesGroupBy.sem` where the presence of non-numeric columns would cause an error instead of being dropped (:issue:`38774`)
- Fixed regression in :meth:`.DataFrameGroupBy.diff` raising for ``int8`` and ``int16`` columns (:issue:`39050`)
- Fixed regression in :meth:`DataFrame.groupby` when aggregating an ``ExtensionDType`` that could fail for non-numeric values (:issue:`38980`)
- Fixed regression in :meth:`.Rolling.skew` and :meth:`.Rolling.kurt` modifying the object inplace (:issue:`38908`)
- Fixed regression in :meth:`DataFrame.any` and :meth:`DataFrame.all` not returning a result for tz-aware ``datetime64`` columns (:issue:`38723`)
- Fixed regression in :meth:`DataFrame.apply` with ``axis=1`` using str accessor in apply function (:issue:`38979`)
- Fixed regression in :meth:`DataFrame.replace` raising ``ValueError`` when :class:`DataFrame` has dtype ``bytes`` (:issue:`38900`)
- Fixed regression in :meth:`Series.fillna` that raised ``RecursionError`` with ``datetime64[ns, UTC]`` dtype (:issue:`38851`)
- Fixed regression in comparisons between ``NaT`` and ``datetime.date`` objects incorrectly returning ``True`` (:issue:`39151`)
- Fixed regression in calling NumPy :func:`~numpy.ufunc.accumulate` ufuncs on DataFrames, e.g. ``np.maximum.accumulate(df)`` (:issue:`39259`)
- Fixed regression in repr of float-like strings of an ``object`` dtype having trailing 0's truncated after the decimal (:issue:`38708`)
- Fixed regression that raised ``AttributeError`` with PyArrow versions [0.16.0, 1.0.0) (:issue:`38801`)
- Fixed regression in :func:`pandas.testing.assert_frame_equal` raising ``TypeError`` with ``check_like=True`` when :class:`Index` or columns have mixed dtype (:issue:`39168`)

We have reverted a commit that resulted in several plotting related regressions in pandas 1.2.0 (:issue:`38969`, :issue:`38736`, :issue:`38865`, :issue:`38947` and :issue:`39126`).
As a result, bugs reported as fixed in pandas 1.2.0 related to inconsistent tick labeling in bar plots are again present (:issue:`26186` and :issue:`11465`)

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

.. _whatsnew_121.ufunc_deprecation:

Calling NumPy ufuncs on non-aligned DataFrames
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Before pandas 1.2.0, calling a NumPy ufunc on non-aligned DataFrames (or
DataFrame / Series combination) would ignore the indices, only match
the inputs by shape, and use the index/columns of the first DataFrame for
the result:

.. code-block:: ipython

    In [1]: df1 = pd.DataFrame({"a": [1, 2], "b": [3, 4]}, index=[0, 1])
    In [2]: df2 = pd.DataFrame({"a": [1, 2], "b": [3, 4]}, index=[1, 2])
    In [3]: df1
    Out[3]:
       a  b
    0  1  3
    1  2  4
    In [4]: df2
    Out[4]:
       a  b
    1  1  3
    2  2  4

    In [5]: np.add(df1, df2)
    Out[5]:
       a  b
    0  2  6
    1  4  8

This contrasts with how other pandas operations work, which first align
the inputs:

.. code-block:: ipython

    In [6]: df1 + df2
    Out[6]:
         a    b
    0  NaN  NaN
    1  3.0  7.0
    2  NaN  NaN

In pandas 1.2.0, we refactored how NumPy ufuncs are called on DataFrames, and
this started to align the inputs first (:issue:`39184`), as happens in other
pandas operations and as it happens for ufuncs called on Series objects.

For pandas 1.2.1, we restored the previous behaviour to avoid a breaking
change, but the above example of ``np.add(df1, df2)`` with non-aligned inputs
will now to raise a warning, and a future pandas 2.0 release will start
aligning the inputs first (:issue:`39184`). Calling a NumPy ufunc on Series
objects (eg ``np.add(s1, s2)``) already aligns and continues to do so.

To avoid the warning and keep the current behaviour of ignoring the indices,
convert one of the arguments to a NumPy array:

.. code-block:: ipython

    In [7]: np.add(df1, np.asarray(df2))
    Out[7]:
       a  b
    0  2  6
    1  4  8

To obtain the future behaviour and silence the warning, you can align manually
before passing the arguments to the ufunc:

.. code-block:: ipython

    In [8]: df1, df2 = df1.align(df2)
    In [9]: np.add(df1, df2)
    Out[9]:
         a    b
    0  NaN  NaN
    1  3.0  7.0
    2  NaN  NaN

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

.. _whatsnew_121.bug_fixes:

Bug fixes
~~~~~~~~~

- Bug in :meth:`read_csv` with ``float_precision="high"`` caused segfault or wrong parsing of long exponent strings. This resulted in a regression in some cases as the default for ``float_precision`` was changed in pandas 1.2.0 (:issue:`38753`)
- Bug in :func:`read_csv` not closing an opened file handle when a ``csv.Error`` or ``UnicodeDecodeError`` occurred while initializing (:issue:`39024`)
- Bug in :func:`pandas.testing.assert_index_equal` raising ``TypeError`` with ``check_order=False`` when :class:`Index` has mixed dtype (:issue:`39168`)

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

.. _whatsnew_121.other:

Other
~~~~~

- The deprecated attributes ``_AXIS_NAMES`` and ``_AXIS_NUMBERS`` of :class:`DataFrame` and :class:`Series` will no longer show up in ``dir`` or ``inspect.getmembers`` calls (:issue:`38740`)
- Bumped minimum fastparquet version to 0.4.0 to avoid ``AttributeError`` from numba (:issue:`38344`)
- Bumped minimum pymysql version to 0.8.1 to avoid test failures (:issue:`38344`)
- Fixed build failure on MacOS 11 in Python 3.9.1 (:issue:`38766`)
- Added reference to backwards incompatible ``check_freq`` arg of :func:`testing.assert_frame_equal` and :func:`testing.assert_series_equal` in :ref:`pandas 1.1.0 what's new <whatsnew_110.api_breaking.testing.check_freq>` (:issue:`34050`)

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

.. _whatsnew_121.contributors:

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

.. contributors:: v1.2.0..v1.2.1
