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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_entry(self, entry):
 """ 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. """

        # 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)