From 4f34ed1e262411edc7711601eec10f8f5b540ac0 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 28 Jan 2021 23:42:58 +0700
Subject: [PATCH 01/12] TST: add failing tests

---
 pandas/tests/frame/methods/test_sort_index.py  | 16 ++++++++++++++++
 pandas/tests/series/methods/test_sort_index.py | 14 ++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/pandas/tests/frame/methods/test_sort_index.py b/pandas/tests/frame/methods/test_sort_index.py
index 221296bfd6d76..0ee50979ab0da 100644
--- a/pandas/tests/frame/methods/test_sort_index.py
+++ b/pandas/tests/frame/methods/test_sort_index.py
@@ -761,6 +761,22 @@ def test_sort_index_with_categories(self, categories):
         )
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "ascending",
+        [
+            None,
+            (True, None),
+            (False, 'True'),
+        ],
+    )
+    def test_sort_index_ascending_bad_value_raises(self, ascending):
+        df = DataFrame(np.arange(64))
+        length = len(df.index)
+        df.index = [(i - length / 2) % length for i in range(length)]
+        match = "ascending must be either a bool or a sequence of bools"
+        with pytest.raises(ValueError, match=match):
+            df.sort_index(axis=0, ascending=ascending, na_position="first")
+
 
 class TestDataFrameSortIndexKey:
     def test_sort_multi_index_key(self):
diff --git a/pandas/tests/series/methods/test_sort_index.py b/pandas/tests/series/methods/test_sort_index.py
index ccaa8a797e312..565186c8fe5d7 100644
--- a/pandas/tests/series/methods/test_sort_index.py
+++ b/pandas/tests/series/methods/test_sort_index.py
@@ -198,6 +198,20 @@ def test_sort_index_ascending_list(self):
         expected = ser.iloc[[0, 4, 1, 5, 2, 6, 3, 7]]
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "ascending",
+        [
+            None,
+            (True, None),
+            (False, 'True'),
+        ],
+    )
+    def test_sort_index_ascending_bad_value_raises(self, ascending):
+        ser = Series(range(10), index=[0, 3, 2, 1, 4, 5, 7, 6, 8, 9])
+        match = "ascending must be either a bool or a sequence of bools"
+        with pytest.raises(ValueError, match=match):
+            ser.sort_index(ascending=ascending)
+
 
 class TestSeriesSortIndexKey:
     def test_sort_index_multiindex_key(self):

From 8e40cacb1a5e52911310a0cfac520556b20ca5bf Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 28 Jan 2021 23:43:17 +0700
Subject: [PATCH 02/12] BUG: add ascending kwarg validation

---
 pandas/core/generic.py | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 96b35f1aaab9c..97766c2a276e5 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -4533,6 +4533,8 @@ def sort_index(
 
         inplace = validate_bool_kwarg(inplace, "inplace")
         axis = self._get_axis_number(axis)
+        ascending = validate_ascending(ascending)
+
         target = self._get_axis(axis)
 
         indexer = get_indexer_indexer(
@@ -11772,3 +11774,25 @@ def _doc_params(cls):
     The required number of valid values to perform the operation. If fewer than
     ``min_count`` non-NA values are present the result will be NA.
 """
+
+
+def validate_ascending(
+    ascending: Union[bool, Sequence[bool]],
+) -> Union[bool, Sequence[bool]]:
+    """Validate ``ascending`` kwargs for ``sort_index`` method."""
+    if not isinstance(ascending, (list, tuple)):
+        _check_ascending_element(ascending)
+        return ascending
+
+    for item in ascending:
+        _check_ascending_element(item)
+    return ascending
+
+
+def _check_ascending_element(value):
+    """Ensure that each item in ``ascending`` kwarg is either bool or int."""
+    if (
+        value is None
+        or not isinstance(value, (bool, int))
+    ):
+        raise ValueError("ascending must be either a bool or a sequence of bools")

From 513e0c5cccf5b88afa2f636f273941d2b197d7be Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Fri, 29 Jan 2021 00:19:13 +0700
Subject: [PATCH 03/12] LINT: black

---
 pandas/core/generic.py                         | 5 +----
 pandas/tests/frame/methods/test_sort_index.py  | 2 +-
 pandas/tests/series/methods/test_sort_index.py | 2 +-
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 97766c2a276e5..16e515f4f1b5a 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11791,8 +11791,5 @@ def validate_ascending(
 
 def _check_ascending_element(value):
     """Ensure that each item in ``ascending`` kwarg is either bool or int."""
-    if (
-        value is None
-        or not isinstance(value, (bool, int))
-    ):
+    if value is None or not isinstance(value, (bool, int)):
         raise ValueError("ascending must be either a bool or a sequence of bools")
diff --git a/pandas/tests/frame/methods/test_sort_index.py b/pandas/tests/frame/methods/test_sort_index.py
index 0ee50979ab0da..fb37727a3e023 100644
--- a/pandas/tests/frame/methods/test_sort_index.py
+++ b/pandas/tests/frame/methods/test_sort_index.py
@@ -766,7 +766,7 @@ def test_sort_index_with_categories(self, categories):
         [
             None,
             (True, None),
-            (False, 'True'),
+            (False, "True"),
         ],
     )
     def test_sort_index_ascending_bad_value_raises(self, ascending):
diff --git a/pandas/tests/series/methods/test_sort_index.py b/pandas/tests/series/methods/test_sort_index.py
index 565186c8fe5d7..7d7b32f96839b 100644
--- a/pandas/tests/series/methods/test_sort_index.py
+++ b/pandas/tests/series/methods/test_sort_index.py
@@ -203,7 +203,7 @@ def test_sort_index_ascending_list(self):
         [
             None,
             (True, None),
-            (False, 'True'),
+            (False, "True"),
         ],
     )
     def test_sort_index_ascending_bad_value_raises(self, ascending):

From dd2d191c29085c592957f8ede1a58ef10a26723d Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Fri, 29 Jan 2021 15:43:45 +0700
Subject: [PATCH 04/12] REF: add kwargs none_allowed and int_allowed

---
 pandas/core/generic.py                        | 18 +++-------
 pandas/tests/frame/methods/test_sort_index.py |  2 +-
 .../tests/series/methods/test_sort_index.py   |  2 +-
 pandas/util/_validators.py                    | 36 +++++++++++++++++--
 4 files changed, 39 insertions(+), 19 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 16e515f4f1b5a..778db90fe6232 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11776,20 +11776,10 @@ def _doc_params(cls):
 """
 
 
-def validate_ascending(
-    ascending: Union[bool, Sequence[bool]],
-) -> Union[bool, Sequence[bool]]:
+def validate_ascending(ascending):
     """Validate ``ascending`` kwargs for ``sort_index`` method."""
+    kwargs = {"none_allowed": False, "int_allowed": True}
     if not isinstance(ascending, (list, tuple)):
-        _check_ascending_element(ascending)
-        return ascending
+        return validate_bool_kwarg(ascending, "ascending", **kwargs)
 
-    for item in ascending:
-        _check_ascending_element(item)
-    return ascending
-
-
-def _check_ascending_element(value):
-    """Ensure that each item in ``ascending`` kwarg is either bool or int."""
-    if value is None or not isinstance(value, (bool, int)):
-        raise ValueError("ascending must be either a bool or a sequence of bools")
+    return [validate_bool_kwarg(item, "ascending", **kwargs) for item in ascending]
diff --git a/pandas/tests/frame/methods/test_sort_index.py b/pandas/tests/frame/methods/test_sort_index.py
index fb37727a3e023..849aae1d1e940 100644
--- a/pandas/tests/frame/methods/test_sort_index.py
+++ b/pandas/tests/frame/methods/test_sort_index.py
@@ -773,7 +773,7 @@ def test_sort_index_ascending_bad_value_raises(self, ascending):
         df = DataFrame(np.arange(64))
         length = len(df.index)
         df.index = [(i - length / 2) % length for i in range(length)]
-        match = "ascending must be either a bool or a sequence of bools"
+        match = 'For argument "ascending" expected type bool'
         with pytest.raises(ValueError, match=match):
             df.sort_index(axis=0, ascending=ascending, na_position="first")
 
diff --git a/pandas/tests/series/methods/test_sort_index.py b/pandas/tests/series/methods/test_sort_index.py
index 7d7b32f96839b..8c6f2e2665ec3 100644
--- a/pandas/tests/series/methods/test_sort_index.py
+++ b/pandas/tests/series/methods/test_sort_index.py
@@ -208,7 +208,7 @@ def test_sort_index_ascending_list(self):
     )
     def test_sort_index_ascending_bad_value_raises(self, ascending):
         ser = Series(range(10), index=[0, 3, 2, 1, 4, 5, 7, 6, 8, 9])
-        match = "ascending must be either a bool or a sequence of bools"
+        match = 'For argument "ascending" expected type bool'
         with pytest.raises(ValueError, match=match):
             ser.sort_index(ascending=ascending)
 
diff --git a/pandas/util/_validators.py b/pandas/util/_validators.py
index fa7201a5188a5..b65a331bbf03a 100644
--- a/pandas/util/_validators.py
+++ b/pandas/util/_validators.py
@@ -205,9 +205,39 @@ def validate_args_and_kwargs(fname, args, kwargs, max_fname_arg_count, compat_ar
     validate_kwargs(fname, kwargs, compat_args)
 
 
-def validate_bool_kwarg(value, arg_name):
-    """ Ensures that argument passed in arg_name is of type bool. """
-    if not (is_bool(value) or value is None):
+def validate_bool_kwarg(value, arg_name, none_allowed=True, int_allowed=False):
+    """
+    Ensure that argument passed in arg_name can be interpreted as boolean.
+
+    Parameters
+    ----------
+    value : bool
+        Value to be validated.
+    arg_name : str
+        Name of the argument. To be reflected in the error message.
+    none_allowed : bool, optional
+        Whether to consider None to be a valid boolean.
+    int_allowed : bool, optional
+        Whether to consider integer value to be a valid boolean.
+
+    Returns
+    -------
+    value
+        The same value as input.
+
+    Raises
+    ------
+    ValueError
+        If the value is not a valid boolean.
+    """
+    good_value = is_bool(value)
+    if none_allowed:
+        good_value = good_value or value is None
+
+    if int_allowed:
+        good_value = good_value or isinstance(value, int)
+
+    if not good_value:
         raise ValueError(
             f'For argument "{arg_name}" expected type bool, received '
             f"type {type(value).__name__}."

From f06d5f499647040a1d618cf5df8c7a0da64ce2a4 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Tue, 2 Feb 2021 12:19:21 +0700
Subject: [PATCH 05/12] DOC: add default values to docstring

---
 pandas/util/_validators.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/util/_validators.py b/pandas/util/_validators.py
index b65a331bbf03a..ee918cef124c6 100644
--- a/pandas/util/_validators.py
+++ b/pandas/util/_validators.py
@@ -215,9 +215,9 @@ def validate_bool_kwarg(value, arg_name, none_allowed=True, int_allowed=False):
         Value to be validated.
     arg_name : str
         Name of the argument. To be reflected in the error message.
-    none_allowed : bool, optional
+    none_allowed : bool, default True
         Whether to consider None to be a valid boolean.
-    int_allowed : bool, optional
+    int_allowed : bool, default False
         Whether to consider integer value to be a valid boolean.
 
     Returns

From 4b8da49cc94422bf05c2c34aa348a8f46c4d4e8d Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 11 Feb 2021 18:02:45 +0700
Subject: [PATCH 06/12] REF/TYP: move validate_ascending to _validators

---
 pandas/core/frame.py       |  2 +-
 pandas/core/generic.py     | 17 ++++++-----------
 pandas/core/series.py      | 10 +++++++---
 pandas/core/sorting.py     |  2 +-
 pandas/util/_validators.py | 13 ++++++++++++-
 5 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index c7585b21abe99..637cbb55bad0c 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -5560,7 +5560,7 @@ def sort_index(
         self,
         axis: Axis = 0,
         level: Optional[Level] = None,
-        ascending: bool = True,
+        ascending: Union[Union[bool, int], Sequence[Union[bool, int]]] = True,
         inplace: bool = False,
         kind: str = "quicksort",
         na_position: str = "last",
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 778db90fe6232..526b4fc71bd4a 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -59,7 +59,11 @@
 from pandas.compat.numpy import function as nv
 from pandas.errors import AbstractMethodError, InvalidIndexError
 from pandas.util._decorators import doc, rewrite_axis_style_signature
-from pandas.util._validators import validate_bool_kwarg, validate_fillna_kwargs
+from pandas.util._validators import (
+    validate_ascending,
+    validate_bool_kwarg,
+    validate_fillna_kwargs,
+)
 
 from pandas.core.dtypes.common import (
     ensure_int64,
@@ -4522,7 +4526,7 @@ def sort_index(
         self,
         axis=0,
         level=None,
-        ascending: bool_t = True,
+        ascending: Union[Union[bool_t, int], Sequence[Union[bool_t, int]]] = True,
         inplace: bool_t = False,
         kind: str = "quicksort",
         na_position: str = "last",
@@ -11774,12 +11778,3 @@ def _doc_params(cls):
     The required number of valid values to perform the operation. If fewer than
     ``min_count`` non-NA values are present the result will be NA.
 """
-
-
-def validate_ascending(ascending):
-    """Validate ``ascending`` kwargs for ``sort_index`` method."""
-    kwargs = {"none_allowed": False, "int_allowed": True}
-    if not isinstance(ascending, (list, tuple)):
-        return validate_bool_kwarg(ascending, "ascending", **kwargs)
-
-    return [validate_bool_kwarg(item, "ascending", **kwargs) for item in ascending]
diff --git a/pandas/core/series.py b/pandas/core/series.py
index f75292f32dbca..b54006b80bf0c 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -15,9 +15,11 @@
     Iterable,
     List,
     Optional,
+    Sequence,
     Tuple,
     Type,
     Union,
+    cast,
 )
 import warnings
 
@@ -3039,7 +3041,7 @@ def update(self, other) -> None:
     def sort_values(
         self,
         axis=0,
-        ascending=True,
+        ascending: Union[Union[bool, int], Sequence[Union[bool, int]]] = True,
         inplace: bool = False,
         kind: str = "quicksort",
         na_position: str = "last",
@@ -3217,6 +3219,7 @@ def sort_values(
             )
 
         if is_list_like(ascending):
+            ascending = cast(Sequence[Union[bool, int]], ascending)
             if len(ascending) != 1:
                 raise ValueError(
                     f"Length of ascending ({len(ascending)}) must be 1 for Series"
@@ -3231,7 +3234,8 @@ def sort_values(
 
         # GH 35922. Make sorting stable by leveraging nargsort
         values_to_sort = ensure_key_mapped(self, key)._values if key else self._values
-        sorted_index = nargsort(values_to_sort, kind, ascending, na_position)
+
+        sorted_index = nargsort(values_to_sort, kind, bool(ascending), na_position)
 
         result = self._constructor(
             self._values[sorted_index], index=self.index[sorted_index]
@@ -3249,7 +3253,7 @@ def sort_index(
         self,
         axis=0,
         level=None,
-        ascending: bool = True,
+        ascending: Union[Union[bool, int], Sequence[Union[bool, int]]] = True,
         inplace: bool = False,
         kind: str = "quicksort",
         na_position: str = "last",
diff --git a/pandas/core/sorting.py b/pandas/core/sorting.py
index 2c2e0c16a4482..8354061e6daea 100644
--- a/pandas/core/sorting.py
+++ b/pandas/core/sorting.py
@@ -41,7 +41,7 @@
 def get_indexer_indexer(
     target: Index,
     level: Union[str, int, List[str], List[int]],
-    ascending: bool,
+    ascending: Union[Sequence[Union[bool, int]], Union[bool, int]],
     kind: str,
     na_position: str,
     sort_remaining: bool,
diff --git a/pandas/util/_validators.py b/pandas/util/_validators.py
index ee918cef124c6..289ea63be62e2 100644
--- a/pandas/util/_validators.py
+++ b/pandas/util/_validators.py
@@ -2,7 +2,7 @@
 Module that contains many useful utilities
 for validating data or function arguments
 """
-from typing import Iterable, Union
+from typing import Iterable, Sequence, Union
 import warnings
 
 import numpy as np
@@ -411,3 +411,14 @@ def validate_percentile(q: Union[float, Iterable[float]]) -> np.ndarray:
         if not all(0 <= qs <= 1 for qs in q_arr):
             raise ValueError(msg.format(q_arr / 100.0))
     return q_arr
+
+
+def validate_ascending(
+    ascending: Union[Union[bool, int], Sequence[Union[bool, int]]] = True,
+):
+    """Validate ``ascending`` kwargs for ``sort_index`` method."""
+    kwargs = {"none_allowed": False, "int_allowed": True}
+    if not isinstance(ascending, (list, tuple)):
+        return validate_bool_kwarg(ascending, "ascending", **kwargs)
+
+    return [validate_bool_kwarg(item, "ascending", **kwargs) for item in ascending]

From 836329399c9c80174d2a409eaceef26ad9410cca Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 11 Feb 2021 18:40:47 +0700
Subject: [PATCH 07/12] FIX: add missing import

---
 pandas/core/series.py  | 1 -
 pandas/core/sorting.py | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/series.py b/pandas/core/series.py
index b54006b80bf0c..a3881becbd121 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -3234,7 +3234,6 @@ def sort_values(
 
         # GH 35922. Make sorting stable by leveraging nargsort
         values_to_sort = ensure_key_mapped(self, key)._values if key else self._values
-
         sorted_index = nargsort(values_to_sort, kind, bool(ascending), na_position)
 
         result = self._constructor(
diff --git a/pandas/core/sorting.py b/pandas/core/sorting.py
index 8354061e6daea..d78ccb40b01eb 100644
--- a/pandas/core/sorting.py
+++ b/pandas/core/sorting.py
@@ -10,6 +10,7 @@
     Iterable,
     List,
     Optional,
+    Sequence,
     Tuple,
     Union,
 )

From 25b4119e21190f213166e86951fb57ef99009c08 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 25 Feb 2021 22:02:52 +0700
Subject: [PATCH 08/12] DOC: update docstring in Series.sort_values

---
 pandas/core/series.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/series.py b/pandas/core/series.py
index d623ef0e7a32b..b211328570f5f 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -3119,7 +3119,7 @@ def sort_values(
         axis : {0 or 'index'}, default 0
             Axis to direct sorting. The value 'index' is accepted for
             compatibility with DataFrame.sort_values.
-        ascending : bool, default True
+        ascending : bool or list of bools, default True
             If True, sort values in ascending order, otherwise descending.
         inplace : bool, default False
             If True, perform operation in-place.

From 6a422b2bb74c3079e8c5768279637836472ce9b9 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 25 Feb 2021 22:04:27 +0700
Subject: [PATCH 09/12] DOC: update docstring in DataFrame.sort_index

---
 pandas/core/frame.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 42bc57124d6a7..a39aef9b91662 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -5646,7 +5646,7 @@ def sort_index(
             and 1 identifies the columns.
         level : int or level name or list of ints or list of level names
             If not None, sort on values in specified index level(s).
-        ascending : bool or list of bools, default True
+        ascending : bool or list-like of bools, default True
             Sort ascending vs. descending. When the index is a MultiIndex the
             sort direction can be controlled for each level individually.
         inplace : bool, default False

From 860c8a5bdb09ddc5f45a9e13b1e5d4bf152c0634 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 25 Feb 2021 22:40:09 +0700
Subject: [PATCH 10/12] TST: use lists, reference GH issue

---
 pandas/tests/frame/methods/test_sort_index.py | 5 +++--
 pandas/util/_validators.py                    | 6 +++++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/pandas/tests/frame/methods/test_sort_index.py b/pandas/tests/frame/methods/test_sort_index.py
index 849aae1d1e940..5fa60b55f4e21 100644
--- a/pandas/tests/frame/methods/test_sort_index.py
+++ b/pandas/tests/frame/methods/test_sort_index.py
@@ -765,11 +765,12 @@ def test_sort_index_with_categories(self, categories):
         "ascending",
         [
             None,
-            (True, None),
-            (False, "True"),
+            [True, None],
+            [False, "True"],
         ],
     )
     def test_sort_index_ascending_bad_value_raises(self, ascending):
+        # GH 39434
         df = DataFrame(np.arange(64))
         length = len(df.index)
         df.index = [(i - length / 2) % length for i in range(length)]
diff --git a/pandas/util/_validators.py b/pandas/util/_validators.py
index 289ea63be62e2..087dccfadcce1 100644
--- a/pandas/util/_validators.py
+++ b/pandas/util/_validators.py
@@ -2,7 +2,11 @@
 Module that contains many useful utilities
 for validating data or function arguments
 """
-from typing import Iterable, Sequence, Union
+from typing import (
+    Iterable,
+    Sequence,
+    Union,
+)
 import warnings
 
 import numpy as np

From a51a343841ff07f8a5aef0d43e950a73283ba033 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Thu, 25 Feb 2021 23:23:27 +0700
Subject: [PATCH 11/12] DOC: update docstring in Series.sort_index

---
 pandas/core/series.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/series.py b/pandas/core/series.py
index b211328570f5f..5fece72ccddca 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -3332,7 +3332,7 @@ def sort_index(
             Axis to direct sorting. This can only be 0 for Series.
         level : int, optional
             If not None, sort on values in specified index level(s).
-        ascending : bool or list of bools, default True
+        ascending : bool or list-like of bools, default True
             Sort ascending vs. descending. When the index is a MultiIndex the
             sort direction can be controlled for each level individually.
         inplace : bool, default False

From 6b430f818d79fbaa7c00b37b290ce8eb1a498eba Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <ivanovmg@gmail.com>
Date: Fri, 26 Feb 2021 19:00:50 +0700
Subject: [PATCH 12/12] DOC: add whatsnew entry

---
 doc/source/whatsnew/v1.2.3.rst | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.2.3.rst b/doc/source/whatsnew/v1.2.3.rst
index 28fc83459b69d..f72ee78bf243a 100644
--- a/doc/source/whatsnew/v1.2.3.rst
+++ b/doc/source/whatsnew/v1.2.3.rst
@@ -19,7 +19,11 @@ Fixed regressions
 - Fixed regression in nullable integer unary ops propagating mask on assignment (:issue:`39943`)
 - Fixed regression in :meth:`DataFrame.__setitem__` not aligning :class:`DataFrame` on right-hand side for boolean indexer (:issue:`39931`)
 - Fixed regression in :meth:`~DataFrame.to_json` failing to use ``compression`` with URL-like paths that are internally opened in binary mode or with user-provided file objects that are opened in binary mode (:issue:`39985`)
--
+- Fixed regression in :meth:`~Series.sort_index` and :meth:`~DataFrame.sort_index`,
+  which exited with an ungraceful error when having kwarg ``ascending=None`` passed (:issue:`39434`).
+  Passing ``ascending=None`` is still considered invalid,
+  and the new error message suggests a proper usage
+  (``ascending`` must be a boolean or a list-like boolean).
 
 .. ---------------------------------------------------------------------------