From b33a6d0e7af2f8f26a92bab6eb8216882f5dd50a Mon Sep 17 00:00:00 2001
From: tp <contribute@tensortable.com>
Date: Mon, 12 Oct 2020 23:08:21 +0100
Subject: [PATCH 1/4] CLN: clean Index._id

---
 pandas/core/indexes/base.py            | 8 ++++----
 pandas/core/indexes/multi.py           | 4 +++-
 pandas/tests/arithmetic/test_object.py | 3 ++-
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index b3f5fb6f0291a..6495eb891bc0c 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -238,7 +238,7 @@ def _outer_indexer(self, left, right):
 
     _typ = "index"
     _data: Union[ExtensionArray, np.ndarray]
-    _id = None
+    _id: _Identity
     _name: Label = None
     # MultiIndex.levels previously allowed setting the index name. We
     # don't allow this anymore, and raise if it happens rather than
@@ -453,8 +453,9 @@ def _simple_new(cls, values, name: Label = None):
         result._index_data = values
         result._name = name
         result._cache = {}
+        result._reset_identity()
 
-        return result._reset_identity()
+        return result
 
     @cache_readonly
     def _constructor(self):
@@ -561,12 +562,11 @@ def is_(self, other) -> bool:
         # use something other than None to be clearer
         return self._id is getattr(other, "_id", Ellipsis) and self._id is not None
 
-    def _reset_identity(self):
+    def _reset_identity(self) -> None:
         """
         Initializes or resets ``_id`` attribute with new object.
         """
         self._id = _Identity()
-        return self
 
     def _cleanup(self):
         self._engine.clear_mapping()
diff --git a/pandas/core/indexes/multi.py b/pandas/core/indexes/multi.py
index 2ce4538a63d25..38a0d18ac732d 100644
--- a/pandas/core/indexes/multi.py
+++ b/pandas/core/indexes/multi.py
@@ -316,7 +316,9 @@ def __new__(
             new_codes = result._verify_integrity()
             result._codes = new_codes
 
-        return result._reset_identity()
+        result._reset_identity()
+
+        return result
 
     def _validate_codes(self, level: List, code: List):
         """
diff --git a/pandas/tests/arithmetic/test_object.py b/pandas/tests/arithmetic/test_object.py
index 02cb4f4d7a606..e0c03f28f7af5 100644
--- a/pandas/tests/arithmetic/test_object.py
+++ b/pandas/tests/arithmetic/test_object.py
@@ -343,8 +343,9 @@ def _simple_new(cls, values, name=None, dtype=None):
         result._index_data = values
         result._name = name
         result._calls = 0
+        result._reset_identity()
 
-        return result._reset_identity()
+        return result
 
     def __add__(self, other):
         self._calls += 1

From 0f5fc5dd384536664e9908f0e0cadcd2a76f5079 Mon Sep 17 00:00:00 2001
From: tp <contribute@tensortable.com>
Date: Mon, 12 Oct 2020 23:59:57 +0100
Subject: [PATCH 2/4] add id class

---
 pandas/core/indexes/base.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 6495eb891bc0c..c365078f8a5d7 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -139,7 +139,10 @@ def index_arithmetic_method(self, other):
 
 
 _o_dtype = np.dtype(object)
-_Identity = object
+
+
+class _Identity:
+    pass
 
 
 def _new_Index(cls, d):

From f49c97e82b57fd1d14a5de4e719251f2a9aa81fb Mon Sep 17 00:00:00 2001
From: tp <contribute@tensortable.com>
Date: Tue, 13 Oct 2020 09:00:26 +0100
Subject: [PATCH 3/4] use typing.NewType

---
 pandas/core/indexes/base.py | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index c365078f8a5d7..aa1f304916a32 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -9,6 +9,7 @@
     FrozenSet,
     Hashable,
     List,
+    NewType,
     Optional,
     Sequence,
     Tuple,
@@ -141,8 +142,7 @@ def index_arithmetic_method(self, other):
 _o_dtype = np.dtype(object)
 
 
-class _Identity:
-    pass
+_Identity = NewType("_Identity", object)
 
 
 def _new_Index(cls, d):
@@ -562,14 +562,13 @@ def is_(self, other) -> bool:
         --------
         Index.identical : Works like ``Index.is_`` but also checks metadata.
         """
-        # use something other than None to be clearer
-        return self._id is getattr(other, "_id", Ellipsis) and self._id is not None
+        return self._id is getattr(other, "_id", None)
 
     def _reset_identity(self) -> None:
         """
         Initializes or resets ``_id`` attribute with new object.
         """
-        self._id = _Identity()
+        self._id = _Identity(object())
 
     def _cleanup(self):
         self._engine.clear_mapping()

From 851c797361b226a9557e174210ca82fa6043d0ef Mon Sep 17 00:00:00 2001
From: tp <contribute@tensortable.com>
Date: Tue, 13 Oct 2020 09:12:52 +0100
Subject: [PATCH 4/4] avoid getattr in Index.is_

---
 pandas/core/indexes/base.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index aa1f304916a32..d180945d85d00 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -562,7 +562,10 @@ def is_(self, other) -> bool:
         --------
         Index.identical : Works like ``Index.is_`` but also checks metadata.
         """
-        return self._id is getattr(other, "_id", None)
+        try:
+            return self._id is other._id
+        except AttributeError:
+            return False
 
     def _reset_identity(self) -> None:
         """