code: def add_order(self, order):
          
          # This key is used to group the orders based on region.
          key = '%s_%s' % (order.region_id, order.type_id)
          if not self._orders.has_key(key):
              # We don't have any orders for this yet. Prep the region+item
              # combo by instantiating a new MarketItemsInRegionList for
              # the MarketOrders.
              self.set_empty_region(
                  order.region_id,
                  order.type_id,
                  order.generated_at
              )
  
          # The MarketOrder gets stuffed into the MarketItemsInRegionList for this
          # item+region combo.
          self._orders[key].add_order(order)
docs: Adds a MarketOrder instance to the list of market orders contained
          within this order list. Does some behind-the-scenes magic to get it
          all ready for serialization.
  
          :param MarketOrder order: The order to add to this order list.