shoppingCarts = {
  'joe' : [ 'milk', 'cookies', 'spinach' ],
  'amy' : ['carrots', 'flour', 'sugar', 'milk', 'cereal' ] }

priceList = { 'milk':1.49, 'cookies':2.00, 'spinach':0.49, 'carrots':1.00,
              'flour' : 2.49, 'sugar' : 2.29, 'cereal' : 1.79 }

def cartTotal(cart, priceDict):
  total = 0
  for item in cart:
    total = total + priceDict[item]
  return total

def customerTotal(customer, carts, prices):
  cart = carts[customer]
  return cartTotal(cart, prices)

def cartTotals(carts, prices):
  result = {}
  for customer in carts.keys():
    result[customer] = customerTotal(customer, carts, prices)
  return result