pandas dataframe set index from column code example

Example 1: add an index column pandas

import numpy as np
import pandas as pd
df = pd.DataFrame({'month': [2, 5, 8, 10],
                   'year': [2017, 2019, 2018, 2019],
                   'sale': [60, 45, 90, 36]})
df.set_index('month')

Example 2: how to change indeces in pandas dataframe

>>> df = pd.DataFrame({'month': [1, 4, 7, 10],
...                    'year': [2012, 2014, 2013, 2014],
...                    'sale': [55, 40, 84, 31]})
>>> df
   month  year  sale
0      1  2012    55
1      4  2014    40
2      7  2013    84
3     10  2014    31