BUG: Fix sorting by column named None in DataFrame.sort_values (GH#61512) (pandas-dev#61517)

BUG: Allow sorting by column named None in DataFrame.sort_values (GH#61512)

Author: iabhi4

doc/source/whatsnew/v3.0.0.rst

@@ -891,6 +891,7 @@ Other
 - Bug in :meth:`DataFrame.query` which raised an exception when querying integer column names using backticks. (:issue:`60494`)
 - Bug in :meth:`DataFrame.shift` where passing a ``freq`` on a DataFrame with no columns did not shift the index correctly. (:issue:`60102`)
 - Bug in :meth:`DataFrame.sort_index` when passing ``axis="columns"`` and ``ignore_index=True`` and ``ascending=False`` not returning a :class:`RangeIndex` columns (:issue:`57293`)
+- Bug in :meth:`DataFrame.sort_values` where sorting by a column explicitly named ``None`` raised a ``KeyError`` instead of sorting by the column as expected. (:issue:`61512`)
 - Bug in :meth:`DataFrame.transform` that was returning the wrong order unless the index was monotonically increasing. (:issue:`57069`)
 - Bug in :meth:`DataFrame.where` where using a non-bool type array in the function would return a ``ValueError`` instead of a ``TypeError`` (:issue:`56330`)
 - Bug in :meth:`Index.sort_values` when passing a key function that turns values into tuples, e.g. ``key=natsort.natsort_key``, would raise ``TypeError`` (:issue:`56081`)

pandas/core/generic.py

@@ -1645,11 +1645,7 @@ def _is_label_reference(self, key: Level, axis: Axis = 0) -> bool:
         axis_int = self._get_axis_number(axis)
         other_axes = (ax for ax in range(self._AXIS_LEN) if ax != axis_int)
 
-        return (
-            key is not None
-            and is_hashable(key)
-            and any(key in self.axes[ax] for ax in other_axes)
-        )
+        return is_hashable(key) and any(key in self.axes[ax] for ax in other_axes)
 
     @final
     def _is_label_or_level_reference(self, key: Level, axis: AxisInt = 0) -> bool:

pandas/tests/frame/methods/test_sort_values.py

@@ -630,6 +630,13 @@ def test_sort_values_no_op_reset_index(self):
         expected = DataFrame({"A": [10, 20], "B": [1, 5]})
         tm.assert_frame_equal(result, expected)
 
+    def test_sort_by_column_named_none(self):
+        # GH#61512
+        df = DataFrame([[3, 1], [2, 2]], columns=[None, "C1"])
+        result = df.sort_values(by=None)
+        expected = DataFrame([[2, 2], [3, 1]], columns=[None, "C1"], index=[1, 0])
+        tm.assert_frame_equal(result, expected)
+
 
 class TestDataFrameSortKey:  # test key sorting (issue 27237)
     def test_sort_values_inplace_key(self, sort_by_key):