def get_next_id(self):
        try:
            query = {'_id': 'last_id'}
            update = {'$inc': {'id': 1}}
            fn = self.db.internal.find_and_modify
            row = fn(query, update, upsert=True, new=True)
        except Exception as e:
            raise DatabaseException(e)
        return row['id']
def stroke_rectangle(self, x, y, w, h):
		self.line(x,y,w,True)
		self.line(x,y+h-1,w,True)
		self.line(x,y,h,False)
		self.line(x+w-1,y,h,False)