Assume you are given a dictionary prices that maps item names (str) to prices (numbers), and a list order of item names (str). Every name in order is guaranteed to be a key of prices, and a name may appear more than once.
Write the function order_total(prices, order) that returns the total cost of the order: the price of every name in order, added up. An empty order costs 0. The prices dictionary must be left unchanged.
menu = {'apple': 1.25, 'bread': 3.50, 'milk': 2.0} order_total(menu, ['bread', 'apple', 'bread']) # 8.25 order_total(menu, ['milk']) # 2.0 order_total(menu, []) # 0