add column in pandas as index code example

Example 1: how to add the column to the beginning of dataframe

# Third position would be at index 2, because of zero-indexing.
df.insert(2, 'new-col', data)

Example 2: 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')