add code sample for pandas-dev#37343

Author: simonjayhawkins

bisect/37343.py

@@ -0,0 +1,23 @@
+import pandas as pd
+
+print(pd.__version__)
+
+
+class SubclassedDataFrame2(pd.DataFrame):
+
+    # temporary properties
+    _internal_names = pd.DataFrame._internal_names + ["internal_cache"]
+    _internal_names_set = set(_internal_names)
+
+    # normal properties
+    _metadata = ["added_property"]
+
+    @property
+    def _constructor(self):
+        return SubclassedDataFrame2
+
+
+df = SubclassedDataFrame2({"A": [1, 2, 3], "B": [1, 1, 2], "C": [7, 8, 9]})
+df.added_property = "hello"
+for i, d in df.groupby("B"):
+    assert d.added_property == "hello"