Simple and agnostic session based cart for Django

django_minicart.py

# -*- coding: utf-8 -*-
#
# No Rights Reserved
# http://creativecommons.org/publicdomain/zero/1.0/

"""Agnostic minimal session based cart for Django.

Just copy-n-paste this snippet to your project.
See `Cart` class reference below for details.

"""
import decimal


def column(name):
    return lambda x: x[name]


class Cart(object):
    """Agnostic minimal session based cart for Django.

    Basic usage example - in views::

        from my_app.models import Product, Order

        def shop_view(request):
            # How to get cart object
            cart = Cart.get_cart(request)
            products = Product.objects.all()
            return render(request, 'my_shop.html', {'cart': cart, 'products': products})

        def add_product_view(request):
            cart = Cart.get_cart(request)

            if request.method == 'POST':
                pk = request.POST['pk']
                quantity = request.POST['quantity']
                product = get_object_or_404(Product, pk=pk)
                # How to add item to cart
                cart.add_item(key=product.pk, quantity=quantity,
                              price=product.price, info={'title': product.title})

        def create_order(request):
            # How to get items in cart and create order
            cart = Cart.get_cart(request)
            products = Product.objects.filter(id__in=cart.get_keys())
            for product in products:
                cart_item = cart.get_item(product.pk)
                # Here's our knowledge edge, you should manually add product
                # to your custom Order model ...

    Usage example - in templates::

        {% for item in cart.get_items %}
            <p>
                {{ item.info.title }}: {{ item.quantity }} x {{ item.price }} = {{ item.total }}
            </p>
        {% empty %}
            Cart is empty.
        {% endfor %}
    """
    session_key = 'cart'

    def __init__(self, **data):
        self._data = data

    @classmethod
    def get_cart(cls, request):
        data = request.session.setdefault(cls.session_key, {})
        return cls(**data)

    @classmethod
    def delete_cart(cls, request):
        if cls.session_key in request.session:
            del request.session[cls.session_key]

    def save(self, request):
        request.session[self.session_key] = self._data

    def delete(self, request):
        self.delete_cart(request)

    def clear(self):
        if 'items' in self._data:
            del self._data['items']

    def add_item(self, key=None, quantity=None, price=None, info=None):
        keys, items = self.get_keys(), self.get_items()
        price = decimal.Decimal(price or '0.00')
        quantity = 1 if quantity is None else int(quantity)

        if key in keys:
            item = items[keys.index(key)]
        else:
            item = {
                'key': key,
                'quantity': 0,
                'price': price,
                'total': 0,
                'info': info or {}
            }
            items.append(item)

        item['quantity'] = item['quantity'] + quantity
        item['total'] = item['quantity'] * item['price']

    def del_item(self, key):
        keys, items = self.get_keys(), self.get_items()
        if key in keys:
            del items[keys.index(key)]

    def get_item(self, key):
        keys, items = self.get_keys(), self.get_items()
        if key in keys:
            return items[keys.index(key)]        

    def get_items(self):
        return self._data.setdefault('items', [])

    def get_keys(self):
        return map(column('key'), self.get_items())

    def get_total(self):
        return sum(map(column('total'), self.get_items()))