如何将类对象追加到列表

Question

After instantiating a deck ( deck = Deck() ), calling deck.show_deck() just prints out "two of diamonds" 52 times. The 'copy' part is as per this answer , but doesn't seem to help. Any suggestions?

import copy
from card import Card

class Deck:

    card_ranks = ['ace','king','queen','jack','ten','nine','eight','seven','six','five','four','three','two']
    card_suites = ['clubs','hearts','spades','diamonds']

    deck = []   

    def __init__(self):
        #create a deck of 52 cards

        for suite in Deck.card_suites:
            for rank in Deck.card_ranks:
                Deck.deck.append(copy.deepcopy(Card(card_rank=rank, card_suite=suite)))



    def show_deck(self):
        for item in Deck.deck:
            print item.get_name()

Card:

class Card:

    card_name = ''

    def __init__(self, card_rank, card_suite):
        self.card_rank = card_rank.lower()
        self.card_suite = card_suite.lower()
        Card.card_name = card_rank + " of " + card_suite

    def get_name(self):
        return Card.card_name

Answer 1

The problem here is that the Card class has a name variable which is shared with all instances of the Card class.

When you have:

class Card:

    card_name = ''

This means that all Card objects will have the same name ( card_name ) which is almost surely not what you want.

You have to make the name be part of the instance instead like so:

class Card:
    def __init__(self, card_rank, card_suite):
        self.card_rank = card_rank.lower()
        self.card_suite = card_suite.lower()
        self.card_name = card_rank + " of " + card_suite

    def get_name(self):
        return self.card_name

You will find that the deepcopy is not needed, nor was it ever needed, but it does show you that deepcopy will not allow you to keep different states of class variables.

Further I would recommend you change Card to have it's own __str__ method if you want to print it out:

class Card:
    def __init__(self, card_rank, card_suite):
        self.card_rank = card_rank.lower()
        self.card_suite = card_suite.lower()

    def __str__(self):
        return "{0} of {1}".format(card_rank, card_suit)

This uses the Python language itself to print the class and has the upside that your class will now work properly in print statements and in conversions to strings. So instead of:

print some_card.get_name()

you could do

print some_card

Answer 2

To expand on what shuttle87 said:

class Card:

    card_name = ''

makes card_name a static variable (shared between all instances of that class)

Once you make the variable non-static (by using self.card_name in the __init__ method) you won't have to worry about the copy part as each instance of the card class will have it's own unique name

On that note, the deck in Deck is also static in your code.

from card import Card

class Deck:
    # these 2 can be static, they never change between copies of the deck class
    card_ranks = ['ace','king','queen','jack','ten','nine','eight','seven','six','five','four','three','two']
    card_suites = ['clubs','hearts','spades','diamonds']

    def __init__(self):
        # this shouldn't be static since you might want to shuffle them 
        # or do other things that make them unique for each deck
        self.cards = []

        for suite in Deck.card_suites:
            for rank in Deck.card_ranks:
                self.cards.append(Card(rank, suite))

    def show_deck(self):
        for item in self.cards:
            print item

---

class Card:
    def __init__(self, rank, suite):
        self.rank = rank
        self.suite = suite

    def __str__(self):
        return self.rank + ' of ' + self.suite

---

#! python2

from deck import Deck

def main():
    deck = Deck()

    deck.show_deck()

if __name__ == '__main__':
    main()

---

ace of clubs
king of clubs
queen of clubs
jack of clubs
...