code sample for pandas-dev#45621

Author: simonjayhawkins

bisect/45621.py

@@ -0,0 +1,15 @@
+# BUG: 1.4.0 does not preserve initially empty Index and appended by loc assignment. #45621
+
+import pandas as pd
+
+print(pd.__version__)
+
+df = pd.DataFrame(columns=["a", "b"]).set_index("a")
+print(df.index, id(df.index))  # Index([], dtype='object', name='a') 4644041536
+
+df.loc[0] = {"b": 0}
+result = df.index
+print(result, id(df.index))  # Int64Index([0], dtype='int64') 4726025904
+
+expected = pd.Index([0], dtype="int64", name="a")
+pd.testing.assert_index_equal(result, expected)