old_contents: from decimal import Decimal
  from django.conf import settings
  from ..shop.models import Product
  
  
  class Cart(object):
  
      def __init__(self, request):
          self.session = request.session
          cart = self.session.get(settings.CART_SESSION_ID)
          if not cart:
              cart = self.session[settings.CART_SESSIO_ID] = {}
          self.cart = cart
  
      def add(self, product, quantity=1, update_quantity=False):
          product_id = str(product.id)
          if product_id not in self.cart:
              self.cart[product_id] = {'quantity': 0,
                                       'price': str(product.price)}
          if update_quantity:
              self.cart[product_id]['quantity'] = quantity
          else:
              self.cart[product_id]['quantity'] += quantity
          self.save()
  
      def save(self):
          self.session[settings.CART_SESSION_ID] = self.cart
          self.session.modified = True
  
      def remove(self, product):
          product_id = str(product.id)
          if product_id in self.cart:
              del self.cart[product_id]
              self.save()
  
      def __iter__(self):
          product_ids = self.cart.keys()
          products = Product.objects.filter(id__in=product_ids)
          for product in products:
              self.cart[str(product.id)]['product'] = product
  
          for item in self.cart.values():
              item['price'] = Decimal(item['price'])
              item['total_price'] = item['price'] * item['quantity']
  
      def __len__(self):
          return sum(item['quantity'] for item in self.cart.values())
  
      def get_total_price(self):
          return sum(Decimal(item['price']) * item['quantity'] for item in self.cart.values())
  
      def clear(self):
          del self.session[settings.CART_SESSION_ID]
          self.session.modified = True
  
new_contents: from decimal import Decimal
  from django.conf import settings
  
  from ..shop.models import Product
  
  
  class Cart(object):
  
      def __init__(self, request):
          self.session = request.session
          cart = self.session.get(settings.CART_SESSION_ID)
          if not cart:
              cart = self.session[settings.CART_SESSION_ID] = {}
          self.cart = cart
  
      def add(self, product, quantity=1, update_quantity=False):
          product_id = str(product.id)
          if product_id not in self.cart:
              self.cart[product_id] = {'quantity': 0,
                                       'price': str(product.price)}
          if update_quantity:
              self.cart[product_id]['quantity'] = quantity
          else:
              self.cart[product_id]['quantity'] += quantity
          self.save()
  
      def save(self):
          self.session[settings.CART_SESSION_ID] = self.cart
          self.session.modified = True
  
      def remove(self, product):
          product_id = str(product.id)
          if product_id in self.cart:
              del self.cart[product_id]
              self.save()
  
      def __iter__(self):
          product_ids = self.cart.keys()
          products = Product.objects.filter(id__in=product_ids)
          for product in products:
              self.cart[str(product.id)]['product'] = product
  
          for item in self.cart.values():
              item['price'] = Decimal(item['price'])
              item['total_price'] = item['price'] * item['quantity']
              yield item
  
      def __len__(self):
          return sum(item['quantity'] for item in self.cart.values())
  
      def get_total_price(self):
          return sum(Decimal(item['price']) * item['quantity'] for item in self.cart.values())
  
      def clear(self):
          del self.session[settings.CART_SESSION_ID]
          self.session.modified = True
  
subject: Fix Cart class