You can iterate over each row and create a new dataframe and then concatenate them together
pd.concat([pd.DataFrame({'Start': pd.date_range(row.Start, row.End, freq='W-SAT'),
'Note': row.Note,
'Item': row.Item}, columns=['Start', 'Note', 'Item'])
for i, row in df.iterrows()], ignore_index=True)
Start Note Item
0 2016-10-22 Z A
1 2016-10-29 Z A
2 2016-11-05 Z A
3 2017-02-11 W B
4 2017-02-18 W B
5 2017-02-25 W B