deprecate positional args in sort_index

Author: MarcoGorelli

doc/source/whatsnew/v1.3.0.rst

@@ -647,6 +647,7 @@ Deprecations
 - Deprecated setting :attr:`Categorical._codes`, create a new :class:`Categorical` with the desired codes instead (:issue:`40606`)
 - Deprecated behavior of :meth:`DatetimeIndex.union` with mixed timezones; in a future version both will be cast to UTC instead of object dtype (:issue:`39328`)
 - Deprecated using ``usecols`` with out of bounds indices for ``read_csv`` with ``engine="c"`` (:issue:`25623`)
+- Deprecated passing arguments as positional in :meth:`DataFrame.sort_index` and :meth:`Series.sort_index` (:issue:`41485`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/frame.py

@@ -77,6 +77,7 @@
     Appender,
     Substitution,
     deprecate_kwarg,
+    deprecate_nonkeyword_arguments,
     doc,
     rewrite_axis_style_signature,
 )
@@ -6262,6 +6263,7 @@ def sort_values(  # type: ignore[override]
         else:
             return result.__finalize__(self, method="sort_values")
 
+    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self"])
     def sort_index(
         self,
         axis: Axis = 0,

pandas/core/series.py

@@ -51,6 +51,7 @@
 from pandas.util._decorators import (
     Appender,
     Substitution,
+    deprecate_nonkeyword_arguments,
     doc,
 )
 from pandas.util._validators import (
@@ -3434,6 +3435,7 @@ def sort_values(
         else:
             return result.__finalize__(self, method="sort_values")
 
+    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self"])
     def sort_index(
         self,
         axis=0,

pandas/tests/frame/methods/test_sort_index.py

@@ -867,3 +867,13 @@ def test_sort_index_multiindex_sparse_column(self):
         result = expected.sort_index(level=0)
 
         tm.assert_frame_equal(result, expected)
+
+    def test_sort_index_pos_args_deprecation(self):
+        # https://github.com/pandas-dev/pandas/issues/41485
+        df = DataFrame({"a": [1, 2, 3]})
+        msg = (
+            r"Starting with Pandas version 2\.0 all arguments of sort_index "
+            r"except for the argument 'self' will be keyword-only"
+        )
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            df.sort_index(1)

pandas/tests/indexing/test_loc.py

@@ -1352,9 +1352,9 @@ def test_loc_setitem_unsorted_multiindex_columns(self, key):
         expected = DataFrame([[0, 2, 0], [0, 5, 0]], columns=mi)
         tm.assert_frame_equal(obj, expected)
 
-        df = df.sort_index(1)
+        df = df.sort_index(axis=1)
         df.loc[:, key] = np.zeros((2, 2), dtype=int)
-        expected = expected.sort_index(1)
+        expected = expected.sort_index(axis=1)
         tm.assert_frame_equal(df, expected)
 
     def test_loc_setitem_uint_drop(self, any_int_dtype):

pandas/tests/series/methods/test_sort_index.py

@@ -320,3 +320,13 @@ def test_sort_values_key_type(self):
         result = s.sort_index(key=lambda x: x.month_name())
         expected = s.iloc[[2, 1, 0]]
         tm.assert_series_equal(result, expected)
+
+    def test_sort_index_pos_args_deprecation(self):
+        # https://github.com/pandas-dev/pandas/issues/41485
+        ser = Series([1, 2, 3])
+        msg = (
+            r"Starting with Pandas version 2\.0 all arguments of sort_index "
+            r"except for the argument 'self' will be keyword-only"
+        )
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            ser.sort_index(0)