code: def retrieve_all(self):
          
          with sqlite3.connect(self.dbname) as carddb:
              for row in carddb.execute("SELECT code FROM CARDS"):
                  yield self.load_card(row[0])
docs: A generator that iterates over each card in the library database.
  
          This is best used in for loops as it will only load a card from the
          library as needed rather then all at once.