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Python Basic Object-Oriented Python Creating a Memory Game Game Class Part 3

Posted by Deven Schmidt
Deven Schmidt
7,847 Points

How does cards[0] and cards[1] represent matched cards?

def check_match(self, loc1, loc2):
        cards = []
        for card in self.cards:
            if card.location == loc1 or card.location == loc2:
                cards.append(card)
        if cards[0] == cards[1]:
            cards[0].matched = True
            cards[1].matched = True
            return True
        else:
            for card in cards:
                print(f'{card.location}: {card}')
            return False

When printing the self.cards words the first two words are "add" how is this being used to match the cards?

[MOD: added ```python formatting -cf]

2 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

Hey Deven Schmidt, this an excellent question! The answer is found by following how Python passes object references.

The cards[0] and cards[1] hold references to specific cards within the self.cards list.

I’ve added comments and two print statements to show the card ids. If ids match then the objects are the same object. 

    def check_match(self, loc1, loc2):
        print(f”self.card ids: {[id(x) for x in self.cards]}”)
        cards = []
        # self.cards contains all the cards
        for card in self.cards:
            # card references individual cards in self.cards
            if card.location == loc1 or card.location == loc2:
                # card appended references a specific card in self.cards
                cards.append(card)
        if cards[0] == cards[1]:
            # the objects in cards list are references to specific cards in self.cards
            # set the match attribute on these specific cards if the card attribute as seen by the __eq__ method match
           print(f”card[0] is: {id(card[0])}:{card[0].card}, card[1] is: {id(card[1])}:{card[1].card}”)
            cards[0].matched = True
            cards[1].matched = True
            return True
        else:
            for card in cards:
                print(f'{card.location}: {card}')
            return False

Edit: show explicit word value in each card

Post back if you need more help. Good luck!!!

Asher Orr
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Asher Orr
Python Development Techdegree Graduate 9,409 Points
Asher Orr
.a{fill-rule:evenodd;}techdegree seal-36
Asher Orr
Python Development Techdegree Graduate 9,409 Points

Hey Chris, thanks for this response!

I am still confused about this.

def check_match(self, loc1, loc2):
        cards = []
        for card in self.cards:
            if card.location == loc1 or card.location == loc2:
                cards.append(card)
        if cards[0] == cards[1]:

Here's my line of thinking:

def check_match(self, loc1, loc2):
        cards = []
        for card in self.cards:
            if card.location == loc1 or card.location == loc2:
                cards.append(card)
                # The cards appended are references to specific cards in self.cards.
        if cards[0] == cards[1]: 
        # Each card in self.cards is unique: it may share the same word as another card, but they all have different locations.
        # Thus, no card is exactly the same.
        # How could Python interpret the statement "cards[0] == cards[1]" as True? It's 2 different cards being compared.

I see that the objects in the cards list are references to specific cards in self.cards. However, the first card (cards[0]) and the second card being compared (cards[1]) are referencing two separate cards within the self.cards list. I don't see how Python would return "True" for the statement:

if cards[0] == cards[1]:

Any idea on where I'm going wrong here?

Thanks again!

Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

Hey Asher Orr! That’s a very good question. First let me state that the overuse of “card” in this code can be confusing.

Looking back at the Card class video, the Card class defines the comparison method __eq__ to return True if the Card.card (ugh!) attributes of two Card instances are the same. That is, if the word stored in the two cards are the same. These two lines would be equivalent:

# using class __eq__ method
cards[0] == cards[1]
# using explicit comparison
cards[0].card == cards[1].card

I’ll need to edit my answer above to clarify this. Thanks!

Post back if you need more help. Good luck!!!

Deven Schmidt
Deven Schmidt
7,847 Points
Deven Schmidt
Deven Schmidt
7,847 Points

Thank you so much, struggled over that idea for a bit!