REGR: fix return class in _constructor_from_mgr for simple subclasses

pandas/core/frame.py

@@ -646,7 +646,7 @@ def _constructor(self) -> Callable[..., DataFrame]:
         return DataFrame
 
     def _constructor_from_mgr(self, mgr, axes):
-        if self._constructor is DataFrame:
+        if type(self) is DataFrame:
             # we are pandas.DataFrame (or a subclass that doesn't override _constructor)
             return self._from_mgr(mgr, axes=axes)
         else:
@@ -659,7 +659,7 @@ def _sliced_from_mgr(self, mgr, axes) -> Series:
         return Series._from_mgr(mgr, axes)
 
     def _constructor_sliced_from_mgr(self, mgr, axes):
-        if self._constructor_sliced is Series:
+        if type(self) is DataFrame:
             ser = self._sliced_from_mgr(mgr, axes)
             ser._name = None  # caller is responsible for setting real name
             return ser

pandas/core/series.py

@@ -632,7 +632,7 @@ def _constructor(self) -> Callable[..., Series]:
         return Series
 
     def _constructor_from_mgr(self, mgr, axes):
-        if self._constructor is Series:
+        if type(self) is Series:
             # we are pandas.Series (or a subclass that doesn't override _constructor)
             ser = self._from_mgr(mgr, axes=axes)
             ser._name = None  # caller is responsible for setting real name
@@ -657,9 +657,7 @@ def _expanddim_from_mgr(self, mgr, axes) -> DataFrame:
         return DataFrame._from_mgr(mgr, axes=mgr.axes)
 
     def _constructor_expanddim_from_mgr(self, mgr, axes):
-        from pandas.core.frame import DataFrame
-
-        if self._constructor_expanddim is DataFrame:
+        if type(self) is Series:
             return self._expanddim_from_mgr(mgr, axes)
         assert axes is mgr.axes
         return self._constructor_expanddim(mgr)

pandas/tests/frame/methods/test_reindex_like.py

@@ -27,6 +27,9 @@ def test_reindex_like_methods(self, method, expected_values):
         result = df.reindex_like(df, method=method, tolerance=[0, 0, 0, 0])
         tm.assert_frame_equal(df, result)
 
+    @pytest.mark.filterwarnings(
+        "ignore:Passing a BlockManager|Passing a SingleBlockManager:DeprecationWarning"
+    )
     def test_reindex_like_subclass(self):
         # https://github.com/pandas-dev/pandas/issues/31925
         class MyDataFrame(DataFrame):

pandas/tests/frame/test_subclass.py

@@ -773,3 +773,21 @@ def test_constructor_with_metadata():
     )
     subset = df[["A", "B"]]
     assert isinstance(subset, MySubclassWithMetadata)
+
+
+class SimpleSubClass(DataFrame):
+    """A subclass of DataFrame that does not define a constructor."""
+
+
+class TestSubclassWithoutConstructor:
+    def test_copy(self):
+        expected = DataFrame({"a": [1, 2, 3]})
+        result = SimpleSubClass(expected).copy()
+
+        tm.assert_frame_equal(result, expected)
+
+    def test_groupby(self):
+        df = SimpleSubClass(DataFrame({"a": [1, 2, 3]}))
+
+        for _, v in df.groupby("a"):
+            assert isinstance(v, DataFrame)