BUG/API: other object type check in Series/DataFrame.equals

doc/source/whatsnew/v1.1.0.rst

@@ -1095,6 +1095,8 @@ Other
 - Bug in :meth:`DataFrame.__dir__` caused a segfault when using unicode surrogates in a column name (:issue:`25509`)
 - Bug in :meth:`DataFrame.plot.scatter` caused an error when plotting variable marker sizes (:issue:`32904`)
 - :class:`IntegerArray` now implements the ``sum`` operation (:issue:`33172`)
+- Bug in :meth:`DataFrame.equals` and :meth:`Series.equals` in allowing subclasses
+  to be equal (:issue:`34402`).
 - Bug in :class:`Tick` comparisons raising ``TypeError`` when comparing against timedelta-like objects (:issue:`34088`)
 - Bug in :class:`Tick` multiplication raising ``TypeError`` when multiplying by a float (:issue:`34486`)
 

pandas/core/generic.py

@@ -1318,7 +1318,7 @@ def equals(self, other):
         >>> df.equals(different_data_type)
         False
         """
-        if not isinstance(other, self._constructor):
+        if not (isinstance(other, type(self)) or isinstance(self, type(other))):
             return False
         return self._mgr.equals(other._mgr)
 

pandas/tests/generic/test_generic.py

@@ -872,6 +872,15 @@ def test_equals(self):
         assert a.equals(e)
         assert e.equals(f)
 
+    def test_equals_subclass(self):
+        # https://github.com/pandas-dev/pandas/pull/34402
+        s1 = pd.Series([1, 2, 3])
+        s2 = tm.SubclassedSeries([1, 2, 3])
+
+        # allow subclass in both directions
+        assert s1.equals(s2)
+        assert s2.equals(s1)
+
     def test_pipe(self):
         df = DataFrame({"A": [1, 2, 3]})
         f = lambda x, y: x ** y