Object Oriented Cash Register

Objectives

1. Build a class with instance methods.
2. Call instance methods inside of other instance methods.
3. Use instance methods to track information pertinent to an instance of a class.

Description

We're going to create an Object Oriented Cash Register that can:

• Add items of varying quantities and prices
• Calculate discounts
• Keep track of what's been added to it
• Void the last transaction

Instructions

The CashRegister class is a blueprint that models attributes (adjectives) and methods (verbs) of an actual register. We've written tests to help keep you on track (feel free to look at the register_test file) - make sure to read the messages when they're not passing!

The CashRegister class

Start by building out your empty CashRegister class so that you can create individual instances. The CashRegister class accepts an optional argument for a percentage discount:

cash_register = CashRegister() # instance of CashRegister with discount of 0.
ten_percent_discount_cash_register = CashRegister(10)  # instance of CashRegister with discount of 10%.

Instances of CashRegister should also have a total attribute which keeps track of the total cost, and an items attribute (as a list) that keeps track of the items that have been added to the register.

Adding Items

Items should be able to be added with their title, price and an option quantity using the add_item method

The register should keep track of which items have been purchased and keep a running total of the purchases.

>>>cash_register.add_item("eggs", 0.98)
>>>cash_register.total
.98
>>>cash_register.items
["eggs"]
>>>cash_register.add_item("magazine", 5.00, 3)
>>>cash_register.total
15.98
>>>cash_register.items
["eggs", "magazine", "magazine", "magazine"]

Discounts

Each time a new register is initialized, a discount can be added. This discount does not affect the total until the class method apply_discount is called.

In addition, the apply_discount method should return a message: "After the discount, the total comes to $TOTAL." where TOTAL is the current total for any added items.

If there is no discount for the current register, the returned message should be "There is no discount to apply".

>>>cash_register2=CashRegister(20)
>>>cash_register2.add_item("chicken", 10)
>>>cash_register2.apply_discount()
"After the discount, the total comes to $8.00."
>>>cash_register2.total
8

Void the Last Transaction

The void_last_transaction method will remove the last transaction from the total. You'll need to make an additional attribute and keep track of the number of recent items added to a list and one to keep track of their value.

Make sure your method can handle instances where the last transaction could include a quantity of 1 or greater.

>>>cash_register.add_item("chicken", 10)
>>>cash_register.add_item("tomato", 1.76, 2)
>>>cash_register.items
["chicken", "tomato", "tomato"]
>>>cash_register.void_last_transaction()
>>>cash_register.total
10
>>>cash_register.items
["chicken"]

This is a test-driven lab! Follow along with the tests in register_test.py. By completing one test at a time, you'll end up with a relatively complex class at the end.

You can always run python register_test.py from the command line to clue you into your next step.

For example, if we run it without creating any code, we'll see that we first need to define class called CashRegister

>>>python register_test.py
Traceback (most recent call last):
  File "register_test.py", line 4, in <module>
    from register import CashRegister
ImportError: cannot import name CashRegister

All great developers, take their code one step at a time. Write one piece of functionality and make sure you get a new test to pass before moving on.

Resources

• String Formatting