code sample for pandas-dev#40799

Author: simonjayhawkins

bisect/40799.py

@@ -0,0 +1,28 @@
+# BUG: behavior change in dataframe.shift(, freq=infer) when upgrading from
+# pandas 1.1.5 to 1.2.x #40799
+
+import io
+
+import numpy as np
+
+import pandas as pd
+
+print(pd.__version__)
+
+# replicate the typical data I am reading with pd.rea_csv
+dates = np.arange(0, 600.1, 0.1)
+dateString = "time, count\n"
+for count, time in enumerate(dates):
+    dateString = dateString + "{:0.3f}, {}\n".format(time, count)
+
+
+# create dataframe and convert 'time' as a datetime and put it to index.
+df = pd.read_csv(io.BytesIO(dateString.encode()), sep=",")
+df["date"] = pd.to_datetime(df.time, unit="s")
+df.set_index("date", inplace=True, drop=False)
+print(df)
+
+df.shift(
+    1, freq="infer"
+)  # <-- this is working with pandas 1.1.5 but not any more with 1.2.0 and above
+print(df)