code sample for pandas-dev#42099

Author: simonjayhawkins

bisect/42099.py

@@ -0,0 +1,19 @@
+# BUG: Adding Series to empty DataFrame can reset dtype to float64 #42099
+
+import pandas as pd
+
+print(pd.__version__)
+
+data = pd.array([0, 1, 2, 3], dtype="Int32")
+df = pd.DataFrame({"data": pd.Series(data)})
+
+result = pd.DataFrame(index=df.index)
+
+result.loc[df.index, "data"] = df["data"]
+
+expected_dtype = df["data"].dtype
+dtype = result["data"].dtype
+
+print(dtype)  # prints: float64 <--
+
+assert dtype == expected_dtype