From aaf7f397e1d554b1d33075e49e689d29cbd68868 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Wed, 23 May 2018 23:51:40 +0530
Subject: [PATCH 1/4] Initial commit

GH21149
---
 doc/source/whatsnew/v0.23.1.txt    |  3 ++-
 pandas/core/indexes/base.py        | 13 +++++++-----
 pandas/tests/indexes/test_multi.py | 34 ++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/doc/source/whatsnew/v0.23.1.txt b/doc/source/whatsnew/v0.23.1.txt
index 44f7280d5535f..5d17792ad0dbd 100644
--- a/doc/source/whatsnew/v0.23.1.txt
+++ b/doc/source/whatsnew/v0.23.1.txt
@@ -77,7 +77,8 @@ Indexing
 ^^^^^^^^
 
 - Bug in :meth:`Series.reset_index` where appropriate error was not raised with an invalid level name (:issue:`20925`)
--
+- Bug in :meth:`MultiIndex.set_names` where error was raised for a MultiIndex with self.nlevels == 1 (:issue: `21149`)
+- Bug in comparison operations for :class:`MultiIndex` where error was raised on comparison involving a MultiIndex with self.nlevels == 1 (:issue: `21149`)
 
 I/O
 ^^^
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index f79288c167356..2a02e901b1002 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -96,10 +96,13 @@ def cmp_method(self, other):
         if needs_i8_conversion(self) and needs_i8_conversion(other):
             return self._evaluate_compare(other, op)
 
+        from .multi import MultiIndex
         if is_object_dtype(self) and self.nlevels == 1:
-            # don't pass MultiIndex
-            with np.errstate(all='ignore'):
-                result = ops._comp_method_OBJECT_ARRAY(op, self.values, other)
+            if not isinstance(self, MultiIndex):
+                # don't pass MultiIndex
+                with np.errstate(all='ignore'):
+                    result = ops._comp_method_OBJECT_ARRAY(op,
+                                                           self.values, other)
 
         else:
 
@@ -1383,8 +1386,8 @@ def set_names(self, names, level=None, inplace=False):
                    labels=[[0, 0, 1, 1], [0, 1, 0, 1]],
                    names=[u'baz', u'bar'])
         """
-
-        if level is not None and self.nlevels == 1:
+        from .multi import MultiIndex
+        if level is not None and not isinstance(self, MultiIndex):
             raise ValueError('Level must be None for non-MultiIndex')
 
         if level is not None and not is_list_like(level) and is_list_like(
diff --git a/pandas/tests/indexes/test_multi.py b/pandas/tests/indexes/test_multi.py
index c9f6bc9151d00..9c45c8188c3df 100644
--- a/pandas/tests/indexes/test_multi.py
+++ b/pandas/tests/indexes/test_multi.py
@@ -3291,3 +3291,37 @@ def test_duplicate_multiindex_labels(self):
         with pytest.raises(ValueError):
             ind.set_levels([['A', 'B', 'A', 'A', 'B'], [2, 1, 3, -2, 5]],
                            inplace=True)
+
+    testdata = [
+        (pd.MultiIndex.from_product([[0, 1], [1, 0]]), pd.Series(range(4)), 4),
+        (pd.MultiIndex.from_product([[0, 1]]), pd.Series(range(2)), 2),
+    ]
+
+    @pytest.mark.parametrize("midx,idx,count", testdata)
+    def test_multiindex_compare(self, midx, idx, count):
+        # GH 21149 - change in 'def cmp_method()'
+        expected = pd.Series([True]).repeat(count)
+        expected.reset_index(drop=True, inplace=True)
+        result = pd.Series(midx == midx)
+        tm.assert_series_equal(result, expected)
+        result = (idx == idx)
+        tm.assert_series_equal(result, expected)
+
+        expected = pd.Series([False]).repeat(count)
+        expected.reset_index(drop=True, inplace=True)
+        result = pd.Series(midx > midx)
+        tm.assert_series_equal(result, expected)
+        result = pd.Series(midx == idx)
+        tm.assert_series_equal(result, expected)
+
+        with tm.assert_raises_regex(TypeError, 'not supported'):
+            midx > idx
+
+    def test_multiindex_set_names(self):
+        # GH 21149 - change in 'def set_names()'
+        result = pd.MultiIndex.from_product([[0, 1]])
+        result.set_names('first', level=0, inplace=True)
+        expected = pd.MultiIndex(levels=[[0, 1]],
+                                 labels=[[0, 1]],
+                                 names=['first'])
+        tm.assert_index_equal(result, expected)

From 5cc818728808e6fd2c933dcc6a09213abf3b2e63 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Thu, 24 May 2018 00:02:59 +0530
Subject: [PATCH 2/4] Updated whatsnew to resolve merge conflicts

GH21149
---
 doc/source/whatsnew/v0.23.1.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v0.23.1.txt b/doc/source/whatsnew/v0.23.1.txt
index 5d17792ad0dbd..58cd9640a0770 100644
--- a/doc/source/whatsnew/v0.23.1.txt
+++ b/doc/source/whatsnew/v0.23.1.txt
@@ -77,6 +77,7 @@ Indexing
 ^^^^^^^^
 
 - Bug in :meth:`Series.reset_index` where appropriate error was not raised with an invalid level name (:issue:`20925`)
+- Bug in :func:`interval_range` when ``start``/``periods`` or ``end``/``periods`` are specified with float ``start`` or ``end`` (:issue:`21161`)
 - Bug in :meth:`MultiIndex.set_names` where error was raised for a MultiIndex with self.nlevels == 1 (:issue: `21149`)
 - Bug in comparison operations for :class:`MultiIndex` where error was raised on comparison involving a MultiIndex with self.nlevels == 1 (:issue: `21149`)
 

From 4f5db97ac290b874c6982f3b9b7ba660654cddc9 Mon Sep 17 00:00:00 2001
From: KalyanGokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Thu, 24 May 2018 00:11:21 +0530
Subject: [PATCH 3/4] Reverted some changes to whatsnew

GH21149
---
 doc/source/whatsnew/v0.23.1.txt | 1 -
 1 file changed, 1 deletion(-)

diff --git a/doc/source/whatsnew/v0.23.1.txt b/doc/source/whatsnew/v0.23.1.txt
index 58cd9640a0770..5d17792ad0dbd 100644
--- a/doc/source/whatsnew/v0.23.1.txt
+++ b/doc/source/whatsnew/v0.23.1.txt
@@ -77,7 +77,6 @@ Indexing
 ^^^^^^^^
 
 - Bug in :meth:`Series.reset_index` where appropriate error was not raised with an invalid level name (:issue:`20925`)
-- Bug in :func:`interval_range` when ``start``/``periods`` or ``end``/``periods`` are specified with float ``start`` or ``end`` (:issue:`21161`)
 - Bug in :meth:`MultiIndex.set_names` where error was raised for a MultiIndex with self.nlevels == 1 (:issue: `21149`)
 - Bug in comparison operations for :class:`MultiIndex` where error was raised on comparison involving a MultiIndex with self.nlevels == 1 (:issue: `21149`)
 

From 85f5b9e3e4141554a61086c36039b05cb63b9d01 Mon Sep 17 00:00:00 2001
From: Kalyan Gokhale <4734245+KalyanGokhale@users.noreply.github.com>
Date: Thu, 24 May 2018 07:28:25 +0530
Subject: [PATCH 4/4] Update v0.23.1.txt

---
 doc/source/whatsnew/v0.23.1.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v0.23.1.txt b/doc/source/whatsnew/v0.23.1.txt
index c3cc38e2297c5..99e968d908182 100644
--- a/doc/source/whatsnew/v0.23.1.txt
+++ b/doc/source/whatsnew/v0.23.1.txt
@@ -79,7 +79,7 @@ Indexing
 - Bug in :meth:`Series.reset_index` where appropriate error was not raised with an invalid level name (:issue:`20925`)
 - Bug in :func:`interval_range` when ``start``/``periods`` or ``end``/``periods`` are specified with float ``start`` or ``end`` (:issue:`21161`)
 - Bug in :meth:`MultiIndex.set_names` where error was raised for a MultiIndex with self.nlevels == 1 (:issue: `21149`)
-- Bug in comparison operations for :class:`MultiIndex` where error was raised on comparison involving a MultiIndex with self.nlevels == 1 (:issue: `21149`)
+- Bug in comparison operations for :class:`MultiIndex` where error was raised on equality / inequality comparison involving a MultiIndex with self.nlevels == 1 (:issue: `21149`)
 -
 
 I/O