fix(python): DataFrame descending sorting by single list element (pol…

…a-rs#19233)

py-polars/polars/lazyframe/frame.py

@@ -1369,7 +1369,12 @@ def sort(
         └──────┴─────┴─────┘
         """
         # Fast path for sorting by a single existing column
-        if isinstance(by, str) and not more_by:
+        if (
+            isinstance(by, str)
+            and not more_by
+            and isinstance(descending, bool)
+            and isinstance(nulls_last, bool)
+        ):
             return self._from_pyldf(
                 self._ldf.sort(
                     by, descending, nulls_last, maintain_order, multithreaded

py-polars/tests/unit/dataframe/test_df.py

@@ -303,10 +303,9 @@ def test_dataframe_membership_operator() -> None:
 
 def test_sort() -> None:
     df = pl.DataFrame({"a": [2, 1, 3], "b": [1, 2, 3]})
-    assert_frame_equal(df.sort("a"), pl.DataFrame({"a": [1, 2, 3], "b": [2, 1, 3]}))
-    assert_frame_equal(
-        df.sort(["a", "b"]), pl.DataFrame({"a": [1, 2, 3], "b": [2, 1, 3]})
-    )
+    expected = pl.DataFrame({"a": [1, 2, 3], "b": [2, 1, 3]})
+    assert_frame_equal(df.sort("a"), expected)
+    assert_frame_equal(df.sort(["a", "b"]), expected)
 
 
 def test_sort_multi_output_exprs_01() -> None: