[Tutor] PYTHON OOP First Project - Coke Machine

[Moshe Zadka]

On Thu, 8 Jun 2000, Thomas A. Williams wrote:

> Hi All,
> I'm a newbie to PYTHON. For my first  Python
> project,  I am embarking on a OOP project using
> Python to simulate a Coca-Cola (or Pepsi  :-)
> vending machine.  Does anyone have any suggestions,
> directions, or ideas to get me started?  Is there any
> existing code (any type of vending machine)
> available which I may be able to study?
> Any information will be greatly appreciated.

Well, standard OO design practice is to first think: what does a vending
machine *do*? IOW, what is the interface of a vending machine?

Well, you can have a look at the vending machine, and see items are
available and what each costs. That would imply methods:

.get_products() -> List of products (say strings, at the moment)

and

.cost(item) -> integer

The other thing, a vending machine does *not* show you how much Coke cans
are in the machine, but it does light a LED to show you if an item is not
availble:

.available(item) -> boolean

Now, you should be able to buy from the machine:

.buy(item, account) -> void

What is an account? It is a representation of someone's bank account, so
the coke machine can take out the costs of the item.
What is the interface of an account?

.deposit(amount) -> void
.withdraw(amount) -> void
.available() -> integer

A complete implementation would probably use the pickle module, together
with the shelve module, to present an interface like

>>> user moshez buys coke
>>> user moshez buys coke
Error: no more cokes
>>> user moshez buys sprite
Error: moshez has no more money
>>> user moshez works
>>> user moshez buys sprite

(Use the cmd module for this kind of work. With enough sophistication, you
may write a virtual coke machine, available through the web (use cgi
module for that))

--
Moshe Zadka <moshez@math.huji.ac.il>
http://www.oreilly.com/news/prescod_0300.html
http://www.linux.org.il -- we put the penguin in .com