def card_names(a_deck): return [card[1] for card in a_deck] all_card_names = [] for deck_card_names in [card_names(deck) for deck in decks]: all_card_names+=deck_card_names len(all_card_names) #17052 all_card_names = set(all_card_names) #make them unique len(list(all_card_names)) #642