code: def encode(self, formatter=None):
          
          items = {}
          # The prices are converted to strings, because they may have a
          # type that can't be serialized to JSON (e.g. Decimal).
          for item in self.items.values():
              pk = str(item.obj.pk)
              items[pk] = {
                  'price': str(item.price),
                  'quantity': item.quantity,
                  'total': item.total,
              }
          cart_repr = {
              'items': items,
              'itemCount': self.item_count,
              'totalPrice': str(self.total_price),
          }
          if formatter:
              cart_repr = formatter(cart_repr)
          return JsonResponse(cart_repr)
docs: Return a representation of the cart as a JSON-response.
  
          Parameters
          ----------
          formatter : func, optional
              A function that accepts the cart representation and returns
              its formatted version.
  
          Returns
          -------
          django.http.JsonResponse
  
          Examples
          --------
          Assume that items with primary keys "1" and "4" are already in
          the cart.
  
          >>> cart = Cart(request)
          >>> def format_total_price(cart_repr):
          ...     return intcomma(cart_repr['totalPrice'])
          ...
          >>> json_response = cart.encode(format_total_price)
          >>> json_response.content
          b'{
              "items": {
                  '1': {"price": 100, "quantity": 10, "total": 1000},
                  '4': {"price": 50, "quantity": 20, "total": 1000},
              },
              "itemCount": 2,
              "totalPrice": "2,000",
          }'