code sample for pandas-dev#42390

Author: simonjayhawkins

bisect/42390.py

@@ -0,0 +1,21 @@
+# BUG: Regression on SeriesGrouper using Timestamp index with pandas 1.3.0 #42390
+
+import numpy as np
+import pandas as pd
+
+print(pd.__version__)
+
+def agg(series):
+    if series.isna().values.all():
+        return None
+    return np.sum(series)
+
+
+df = pd.DataFrame([1.0], index=[pd.Timestamp("2018-01-16 00:00:00+00:00")])
+
+result = df.groupby(lambda x: 1).agg(agg)
+print(result)
+
+expected = pd.DataFrame([1.0], index=[1])
+pd.testing.assert_frame_equal(result, expected)
+