code: def contains_info(self, key, value):
          
          if self.library is None:
              return 0
  
          load = self.library.load_card
          matches = 0
          for code in self.cards:
              card = load(code)
              if card.get_info(key) == value:
                  matches += 1
          return matches
docs: Returns how many cards in the deck have the specified value under the
          specified key in their info data.
  
          This method requires a library to be stored in the deck instance and
          will return `None` if there is no library.