df = pd.DataFrame({'month': [1, 4, 7, 10],
'year': [2012, 2014, 2013, 2014],
'sale': [55, 40, 84, 31]})
print(df)
print(df.set_index('month'))
print(df.set_index(['year', 'month']))
first print stmt gives default index,next print stmt gives default index change to month,third print stmt gives year month as index