From a8bcd0fa74048172f6cd311c9875de29617db821 Mon Sep 17 00:00:00 2001
From: Eric Hansen <eric.a.hansen@avanade.com>
Date: Mon, 2 Mar 2020 21:18:08 -0500
Subject: [PATCH 1/2] BUG: Replace isinstance with issubclass in _ensure_type
 (#31925)

Commit pandas-dev/pandas@6fd326d5a249967f9b6be60fc3c5f7366d914684 in
pull request pandas-dev/pandas#30613 added `_ensure_type`, which
utilizes `isinstance`. However, it is reasonable to assume that someone
may want to create a DataFrame subclass. Therefore, `_ensure_type`
should use `issubclass`.
---
 pandas/core/base.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/base.py b/pandas/core/base.py
index f55d9f905945d..40ca70ec7973a 100644
--- a/pandas/core/base.py
+++ b/pandas/core/base.py
@@ -93,7 +93,7 @@ def _ensure_type(self: T, obj) -> T:
 
         Used by type checkers.
         """
-        assert isinstance(obj, type(self)), type(obj)
+        assert issubclass(type(obj), type(self)), type(obj)
         return obj
 
 

From 5ddbea941758df576e5c513764134c2f6a8583eb Mon Sep 17 00:00:00 2001
From: Eric Hansen <eric.a.hansen@avanade.com>
Date: Tue, 3 Mar 2020 13:01:51 -0500
Subject: [PATCH 2/2] TST: Added tests for pandas object ensure type (#31925)

---
 pandas/tests/base/test_base.py | 38 ++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 pandas/tests/base/test_base.py

diff --git a/pandas/tests/base/test_base.py b/pandas/tests/base/test_base.py
new file mode 100644
index 0000000000000..22eb4f03653f6
--- /dev/null
+++ b/pandas/tests/base/test_base.py
@@ -0,0 +1,38 @@
+import pytest
+
+from pandas.core.base import PandasObject
+
+pandas_object = PandasObject()
+
+
+class SubclassPandasObject(PandasObject):
+    pass
+
+
+subclass_pandas_object = SubclassPandasObject()
+
+
+@pytest.mark.parametrize("other_object", [pandas_object, subclass_pandas_object])
+def test_pandas_object_ensure_type(other_object):
+    pandas_object = PandasObject()
+    assert pandas_object._ensure_type(other_object)
+
+
+def test_pandas_object_ensure_type_for_same_object():
+    pandas_object_a = PandasObject()
+    pandas_object_b = pandas_object_a
+    assert pandas_object_a._ensure_type(pandas_object_b)
+
+
+class OtherClass:
+    pass
+
+
+other_class = OtherClass()
+
+
+@pytest.mark.parametrize("other_object", [other_class])
+def test_pandas_object_ensure_type_for_false(other_object):
+    pandas_object = PandasObject()
+    with pytest.raises(AssertionError):
+        assert pandas_object._ensure_type(other_object)