Add whatsnew

Author: howsiwei

doc/source/whatsnew/v1.1.0.rst

@@ -161,6 +161,35 @@ Indexing
 - Bug in :meth:`DatetimeIndex.get_loc` raising ``KeyError`` with converted-integer key instead of the user-passed key (:issue:`31425`)
 - Bug in :meth:`Series.xs` incorrectly returning ``Timestamp`` instead of ``datetime64`` in some object-dtype cases (:issue:`31630`)
 
+Assignment to multiple columns of a DataFrame when some columns do not exist
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Assignment to multiple columns of a :class:`DataFrame` when some of the columns do not exist would previously assign the values to the last column. Now, new columns would be constructed with the right values. (:issue:`13658`)
+
+.. ipython:: python
+
+   df = pd.DataFrame({'a': [0, 1, 2], 'b': [3, 4, 5]})
+   df
+
+*Previous behavior*:
+
+.. code-block:: ipython
+
+   In [3]: df[['a', 'c']] = 1
+   In [4]: df
+   Out[4]:
+      a  b
+   0  1  1
+   1  1  1
+   2  1  1
+
+*New behavior*:
+
+.. ipython:: python
+
+   df[['a', 'c']] = 1
+   df
+
 Missing
 ^^^^^^^