Get a particular item type

            :param ttype: a string which represents the desired type

            :rtype: None or the item object

def get_item_type(self, ttype):
        """
            Get a particular item type

            :param ttype: a string which represents the desired type

            :rtype: None or the item object
        """
        for i in self.map_item:
            if TYPE_MAP_ITEM[i.get_type()] == ttype:
                return i.get_item()
        return None