how to check for error python code example

Example: find the error python

print ("Welcome to the vending machine, type a product code: 1001 or 1002 ")
product_code = int(input())
KitKat_price = 2
doritos_price = 2.5
if (product_code == 1001):
  print("You have selected" , + (product_code))
  print("The price of the Kit Kat is 2$. Insert the neccesary coins")
  customer_money
  customer_money = int(input())
  if customer_money == KitKat_price:
    print("You have inserted 2$, KitKat is dispensing "
  if customer_money > KitKat_price:
    print("You have insterted more than 2$")
  if customer_money < KitKat_price:
    print("You have not inserted enough coins, instert more coins to get the KitKat")
if (product_code == 1002): 
  print("You have selected", + (product_code))
  print("The price of the doritos is 2.5$. Insert the neccesary coins:")
  customer_money = float(input())
  if customer_money > doritos_price:
    print("You have inserted more than 2.5$")
  if customer_money < doritos_price:
    print("You have not insterted enough coins, insert more coins to get the doritos")
  if customer_money == doritos_price:
    print("You have inserted 2$")
    print("Doritos is dispensing")
else:
  print("You have not selected any product code")