how to add an index to a pandas dataframe 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 index in dataframe python

index = [1,2]
df.index = index