import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
excel_file = "dataset.xlsx"
sheet0 = pd.read_excel(excel_file, 'Title Sheet')
sheet3 = pd.read_excel(excel_file, sheet_name='CustomerDemographic')
sheet4 = pd.read_excel(excel_file, sheet_name='CustomerAddress')
sheet1 = pd.read_excel(excel_file, sheet_name='Transactions')
customer_data = pd.concat([sheet3, sheet4, sheet1])
#TODO: Data calculations
pivot = sheet3.groupby(['customer_id']).mean()
bestCustomers = pivot.loc[:,"past_3_years_bike_related_purchases":"tenure"]
But it gives KeyError: 'customer_id' , where is the problem actually ?