page visit funnel pandas

import codecademylib
import pandas as pd

visits = pd.read_csv('visits.csv',
                     parse_dates=[1])
cart = pd.read_csv('cart.csv',
                   parse_dates=[1])
checkout = pd.read_csv('checkout.csv',
                       parse_dates=[1])
purchase = pd.read_csv('purchase.csv',
                       parse_dates=[1])


print(visits.head(),cart.head(),checkout.head(),purchase.head())

visit_cart=pd.merge(visits,cart,how='left')
print(visit_cart)
print(len(visit_cart))

cart_null=visit_cart[visit_cart.cart_time.isnull()]
print(cart_null)
percent_cart=cart_null.user_id.count()/visit_cart.user_id.count()*1.0
print(percent_cart)
percent_cart2=float(len(cart_null))/len(visit_cart)
print(percent_cart2)

cart_check=pd.merge(cart,checkout,how='left')
check_null=cart_check[cart_check.checkout_time.isnull()]
percent_check=float(len(check_null))/len(cart_check)
print(percent_check)

all_data= visits.merge(cart,how='left').merge(checkout,how='left').merge(purchase,how='left')
print(all_data.head())
print('len data',len(all_data))

check_pur=pd.merge(checkout,purchase,how='left')
print(check_pur)
check_pur_row= len(check_pur)
print(check_pur_row)
not_purchase=len(check_pur[check_pur.purchase_time.isnull()])
print(not_purchase)


percent_notpur=float(not_purchase)/check_pur_row
print(percent_notpur)

all_data['time_to_purchase'] = \
    all_data.purchase_time - \
    all_data.visit_time
print(all_data)

print(all_data.time_to_purchase.mean())