code sample for pandas-dev#44866

Author: simonjayhawkins

Diff for: bisect/44866.py

@@ -0,0 +1,40 @@
+# BUG: DataFrame.copy mutates the source dataframe, discarding Series attributes listed in Series._metadata. #44866
+"""
+Metadata wipeout example.
+"""
+
+import pandas as pd
+
+print(pd.__version__)
+
+
+class S(pd.Series):
+    _metadata = ["foo"]
+
+    @property
+    def _constructor(self):
+        return S
+
+    @property
+    def _constructor_expanddim(self):
+        return DF
+
+
+class DF(pd.DataFrame):
+    def __repr__(self):
+        foos = {k: getattr(v, "foo", None) for k, v in self.items()}
+        return super().__repr__() + f"\n{foos=}"
+
+    @property
+    def _constructor(self):
+        return DF
+
+    @property
+    def _constructor_sliced(self):
+        return S
+
+
+df = DF({"a": [1]})
+df["a"].foo = "bar"
+df.copy()  # ``DataFrame.copy`` mutates the data!
+assert hasattr(df["a"], "foo"), "Dataframe mutated by ``copy`` method"