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

Author: iabhi4

doc/source/whatsnew/v3.0.0.rst

@@ -886,6 +886,7 @@ 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/frame.py

@@ -7188,7 +7188,7 @@ def sort_values(
             if key is not None:
                 # error: Incompatible types in assignment (expression has type
                 # "Series", variable has type "ndarray")
-                k = Series(k, name=by[0])  # type: ignore[assignment]
+                k = Series(k, name=by[0])
 
             if isinstance(ascending, (tuple, list)):
                 ascending = ascending[0]

pandas/core/generic.py

@@ -1757,7 +1757,9 @@ def _get_label_or_level_values(self, key: Level, axis: AxisInt = 0) -> ArrayLike
             (ax for ax in range(self._AXIS_LEN) if ax != axis), None
         )
 
-        if self._is_label_reference(key, axis=axis):
+        if axis == 0 and key in self.columns:
+            values = self[key]._values
+        elif self._is_label_reference(key, axis=axis):
             self._check_label_or_level_ambiguity(key, axis=axis)
             if first_other_axes is None:
                 raise ValueError("axis matched all axes")

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):