Python Duplicating values when appending to array in class

Question

This is my first StackOverflow post, so please tell me if I have done anything wrong!

I am trying to make a card game in python and have been told that using a class based system would be best.

Whilst trying to do so, when putting all the cards into a deck, the classes seem to duplicate the values onto the board.cards part of the code.

#definitions and imports
import random

class Card:
    suit = ""
    base = ""

class Hand:
    cards = []
    poweri = 0
    powerii = 0

class Stack:
    cards = []

#instantiates classes
deck = Stack()
board = Stack()

player = Hand()
dealer = Hand()

#creates ordered empty deck
def newdeck(obj):
    for x in ["2","3","4","5","6","7","8","9","A","B","C","D","E"]:
        for y in ["C","D","H","S"]:
            card = Card()
            card.base = x
            card.suit = y
            obj.cards.append(card)


#shuffles deck
def shuffle():
    random.shuffle(deck.cards)


newdeck(deck)
#disabled to make debug easier
#shuffle()


#prints entire deck
print("\nDeck")
for i in range(len(deck.cards)):
    print(deck.cards[i].base, deck.cards[i].suit)
print(len(deck.cards))

#prints entire board
print("\nBoard")
for i in range(len(board.cards)):
    print(board.cards[i].base, board.cards[i].suit)

The program returns this:

Deck
2 C
2 D
2 H
2 S
3 C
3 D
3 H
3 S
4 C
4 D
4 H
4 S
5 C
5 D
5 H
5 S
6 C
6 D
6 H
6 S
7 C
7 D
7 H
7 S
8 C
8 D
8 H
8 S
9 C
9 D
9 H
9 S
A C
A D
A H
A S
B C
B D
B H
B S
C C
C D
C H
C S
D C
D D
D H
D S
E C
E D
E H
E S
52

Board
2 C
2 D
2 H
2 S
3 C
3 D
3 H
3 S
4 C
4 D
4 H
4 S
5 C
5 D
5 H
5 S
6 C
6 D
6 H
6 S
7 C
7 D
7 H
7 S
8 C
8 D
8 H
8 S
9 C
9 D
9 H
9 S
A C
A D
A H
A S
B C
B D
B H
B S
C C
C D
C H
C S
D C
D D
D H
D S
E C
E D
E H
E S

Process returned 0 (0x0)        execution time : 0.314 s
Press any key to continue . . .

Board should be empty???

Regards, Alex

Andrzej Klajnert · Accepted Answer · 2018-11-11 18:03:20Z

1

The Stack.cards is a mutable class attribute. That means, all class instances will have reference to the same object with the same data.

You probably want each object to have its own data. To change it, instantiate cards within __init__() method:

class Stack:
    def __init__(self):
        self.cards = []

answered Nov 11, 2018 at 18:03

Andrzej Klajnert

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1 Comment

rgbalex Over a year ago

Thank you - I didn't realise you had to instantiate them in that way!

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