POS System

Our supermarket sells three items, each of which has a stock-keeping code and a price. Multibuy offers are applicable to some items. Your objective is to implement the logic behind a Point of Sale (POS) system for our supermarket using the Python programming language.

Inventory

Item	Code	Offer
Apple	A	Three for the price of two
Banana	B	Three for £1
Pear	P	None

Tasks

• Create a source file containing a function named checkout that takes a list of item codes and their current prices and returns the total price in pence, after applying any relevant offers. For example checkout(['B', 'A', 'B', 'P', 'B'], {'A': 25, 'B': 40, 'P': 30}) should return 155.
• Create a second source file containing code to verify the behaviour of your checkout function.
• [Optional] Add an object type Checkout to your first source file that can instantiated with the current prices, for example Checkout({'A': 25, 'B': 40, 'P': 30}). It should provide two methods: scan(code) and total(). The latter should be callable at any time to obtain a correct total for the items scanned so far. Add test(s) for Checkout to your second source file.