code: def add_entry(self, entry):
          
          # This key is used to group the orders based on region.
          key = '%s_%s' % (entry.region_id, entry.type_id)
          if not self._history.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(
                  entry.region_id,
                  entry.type_id,
                  entry.generated_at
              )
  
          # The MarketOrder gets stuffed into the MarketItemsInRegionList for this
          # item+region combo.
          self._history[key].add_entry(entry)
docs: Adds a MarketHistoryEntry instance to the list of market history entries
          contained within this instance. Does some behind-the-scenes magic to
          get it all ready for serialization.
  
          :param MarketHistoryEntry entry: The history entry to add to
              instance.