Python Grouping attributes within a class

Question

Let's say that I have a class "shoppingCart". I add items to the shopping cart: eggs, milk, cheese, bread, toothbrush, bacon, dish soap, potato chips, and bottled water.

class shoppingCart(object):
    def __init__(self):
        self.eggs = 12
        self.milk = 2
        self.cheese = 1
        self.bread = 0
        self.toothbrush = 1
        self.bacon = 10
        self.soap = 1
        self.chips = 2
        self.bottlewater = 24

myCart = shoppingCart()

Is it possible to create a group within the class, so that I could identify the number of items in my cart that fall into a specific category? For example, if I wanted to call all the attributes that are beverages (milk, water), or all the things that are non-food (toothbrush, soap), or things that are delicious (cheese, bacon, chips) - how could I go about doing that?

score 2 · Accepted Answer · 2016-07-05 22:13:09Z

You shouldn't do that with only one class. I would create two clases. One would be a cart item, and the other one the shopping cart. For instance:

class cartItem(object):
    def __init__(self, amount=0):
        self.amount = amount
        self._is_beverage = False

    @property
    def is_beverage(self):
        return self._is_beverage

    @is_beverage.setter
    def is_beverage(self, value):
        self._is_beverage = value

And then the shopping cart:

class shoppingCart(object):
    def __init__(self):
        self._cart_items = []

    @property
    def cart_items(self):
        return self._cart_items

    @cart_items.setter
    def cart_items(self, value):
        self._cart_items = value

    def append_cart_item(self, new_cart_item):
        self._cart_items = self._cart_items.append(new_cart_item)

So you'd do:

myCart = shoppingCart()

milk = cartItem(amount=10)
milk.is_beverage = True

coke = cartItem(amount=2)
milk.is_beverage = True

myCart.cart_items = [milk, coke]

chips = CartItem(amount=20)
chips.is_beverage = False

myCart.append_cart_item(chips)

I would even make a specific class for each cart item type (I may improve the example later). I recommend you to learn more about classes and subclasses, for example here: http://www.jesshamrick.com/2011/05/18/an-introduction-to-classes-and-inheritance-in-python/

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