how to set two columns as index in pandas code example

Example 1: set index to column pandas

df = df.set_index('col')
df['col'] = df.index

Example 2: how to change indeces in pandas dataframe

>>> df.set_index('month')
       year  sale
month
1      2012    55
4      2014    40
7      2013    84
10     2014    31