DOC: more info for dtype argument of get_dummies in whatsnew

Author: Scorpil

doc/source/whatsnew/v0.22.0.txt

@@ -24,17 +24,27 @@ Other Enhancements
 
 - Better support for :func:`Dataframe.style.to_excel` output with the ``xlsxwriter`` engine. (:issue:`16149`)
 - :func:`pandas.tseries.frequencies.to_offset` now accepts leading '+' signs e.g. '+1h'. (:issue:`18171`)
-- :func:`pandas.get_dummies` now supports ``dtype`` argument, which forces specific dtype for new columns. (:issue:`18330`)
 
-.. code-block:: ipython
+``get_dummies`` now supports ``dtype`` argument
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-   In [1]: df = pd.DataFrame({'a': [1, 2], 'b': [3, 4], 'c': [5, 6]})
-   In [2]: pd.get_dummies(df, columns=['c'], dtype=bool)
+:func:`get_dummies` function now accepts ``dtype`` argument, which forces specific dtype for new columns. When ``dtype`` is not specified or equals to ``None``, new columns will have dtype ``uint8`` (as before), so this change is backwards compatible. (:issue:`18330`)
 
-   Out[1]:
-      a  b    c_5    c_6
-   0  1  3   True  False
-   1  2  4  False   True
+**Previous behavior**:
+
+.. ipython:: python
+
+   df = pd.DataFrame({'a': [1, 2], 'b': [3, 4], 'c': [5, 6]})
+   pd.get_dummies(df, columns=['c'])
+
+**New behavior**:
+
+.. ipython:: python
+
+   df = pd.DataFrame({'a': [1, 2], 'b': [3, 4], 'c': [5, 6]})
+   pd.get_dummies(df, columns=['c'])
+   pd.get_dummies(df, columns=['c'], dtype=bool)
+   pd.get_dummies(df, columns=['c'], dtype=np.float64)
 
 .. _whatsnew_0220.api_breaking: