Backport PR #25069: REGR: rename_axis with None should remove axis na…

…me (#25079)
pandas-dev · TomAugspurger · Feb 3, 2019 · Jan 26, 2019 · Jan 26, 2019 · Jan 28, 2019
commit c21d32f48e6b6efc9257e187793a19e81d2ac306
diff --git a/doc/source/whatsnew/v0.24.1.rst b/doc/source/whatsnew/v0.24.1.rst
@@ -25,6 +25,7 @@ Fixed Regressions
 - Fixed regression in :func:`read_sql` when passing certain queries with MySQL/pymysql (:issue:`24988`).
 - Fixed regression in :class:`Index.intersection` incorrectly sorting the values by default (:issue:`24959`).
 - Fixed regression in :func:`merge` when merging an empty ``DataFrame`` with multiple timezone-aware columns on one of the timezone-aware columns (:issue:`25014`).
+- Fixed regression in :meth:`Series.rename_axis` and :meth:`DataFrame.rename_axis` where passing ``None`` failed to remove the axis name (:issue:`25034`)
 
 .. _whatsnew_0241.enhancements:
 

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
@@ -61,6 +61,10 @@
         by : str or list of str
             Name or list of names to sort by""")
 
+# sentinel value to use as kwarg in place of None when None has special meaning
+# and needs to be distinguished from a user explicitly passing None.
+sentinel = object()
+
 
 def _single_replace(self, to_replace, method, inplace, limit):
     """
@@ -290,11 +294,16 @@ def _construct_axes_dict_for_slice(self, axes=None, **kwargs):
         d.update(kwargs)
         return d
 
-    def _construct_axes_from_arguments(self, args, kwargs, require_all=False):
+    def _construct_axes_from_arguments(
+            self, args, kwargs, require_all=False, sentinel=None):
         """Construct and returns axes if supplied in args/kwargs.
 
         If require_all, raise if all axis arguments are not supplied
         return a tuple of (axes, kwargs).
+
+        sentinel specifies the default parameter when an axis is not
+        supplied; useful to distinguish when a user explicitly passes None
+        in scenarios where None has special meaning.
         """
 
         # construct the args
@@ -322,7 +331,7 @@ def _construct_axes_from_arguments(self, args, kwargs, require_all=False):
                         raise TypeError("not enough/duplicate arguments "
                                         "specified!")
 
-        axes = {a: kwargs.pop(a, None) for a in self._AXIS_ORDERS}
+        axes = {a: kwargs.pop(a, sentinel) for a in self._AXIS_ORDERS}
         return axes, kwargs
 
     @classmethod
@@ -1089,7 +1098,7 @@ def rename(self, *args, **kwargs):
 
     @rewrite_axis_style_signature('mapper', [('copy', True),
                                              ('inplace', False)])
-    def rename_axis(self, mapper=None, **kwargs):
+    def rename_axis(self, mapper=sentinel, **kwargs):
         """
         Set the name of the axis for the index or columns.
 
@@ -1218,7 +1227,8 @@ class  name
                cat            4         0
                monkey         2         2
         """
-        axes, kwargs = self._construct_axes_from_arguments((), kwargs)
+        axes, kwargs = self._construct_axes_from_arguments(
+            (), kwargs, sentinel=sentinel)
         copy = kwargs.pop('copy', True)
         inplace = kwargs.pop('inplace', False)
         axis = kwargs.pop('axis', 0)
@@ -1231,7 +1241,7 @@ class  name
 
         inplace = validate_bool_kwarg(inplace, 'inplace')
 
-        if (mapper is not None):
+        if (mapper is not sentinel):
             # Use v0.23 behavior if a scalar or list
             non_mapper = is_scalar(mapper) or (is_list_like(mapper) and not
                                                is_dict_like(mapper))
@@ -1254,7 +1264,7 @@ class  name
 
             for axis in lrange(self._AXIS_LEN):
                 v = axes.get(self._AXIS_NAMES[axis])
-                if v is None:
+                if v is sentinel:
                     continue
                 non_mapper = is_scalar(v) or (is_list_like(v) and not
                                               is_dict_like(v))

diff --git a/pandas/tests/frame/test_alter_axes.py b/pandas/tests/frame/test_alter_axes.py
@@ -600,6 +600,26 @@ def test_rename_axis_mapper(self):
         with pytest.raises(TypeError, match='bogus'):
             df.rename_axis(bogus=None)
 
+    @pytest.mark.parametrize('kwargs, rename_index, rename_columns', [
+        ({'mapper': None, 'axis': 0}, True, False),
+        ({'mapper': None, 'axis': 1}, False, True),
+        ({'index': None}, True, False),
+        ({'columns': None}, False, True),
+        ({'index': None, 'columns': None}, True, True),
+        ({}, False, False)])
+    def test_rename_axis_none(self, kwargs, rename_index, rename_columns):
+        # GH 25034
+        index = Index(list('abc'), name='foo')
+        columns = Index(['col1', 'col2'], name='bar')
+        data = np.arange(6).reshape(3, 2)
+        df = DataFrame(data, index, columns)
+
+        result = df.rename_axis(**kwargs)
+        expected_index = index.rename(None) if rename_index else index
+        expected_columns = columns.rename(None) if rename_columns else columns
+        expected = DataFrame(data, expected_index, expected_columns)
+        tm.assert_frame_equal(result, expected)
+
     def test_rename_multiindex(self):
 
         tuples_index = [('foo1', 'bar1'), ('foo2', 'bar2')]

diff --git a/pandas/tests/series/test_alter_axes.py b/pandas/tests/series/test_alter_axes.py
@@ -258,6 +258,17 @@ def test_rename_axis_inplace(self, datetime_series):
         assert no_return is None
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize('kwargs', [{'mapper': None}, {'index': None}, {}])
+    def test_rename_axis_none(self, kwargs):
+        # GH 25034
+        index = Index(list('abc'), name='foo')
+        df = Series([1, 2, 3], index=index)
+
+        result = df.rename_axis(**kwargs)
+        expected_index = index.rename(None) if kwargs else index
+        expected = Series([1, 2, 3], index=expected_index)
+        tm.assert_series_equal(result, expected)
+
     def test_set_axis_inplace_axes(self, axis_series):
         # GH14636
         ser = Series(np.arange(4), index=[1, 3, 5, 7], dtype='int64')