I'm building a blackjack command line game and I've run into a snag. The shuffle feature on my deck class object keeps coming up with IndexError: list index out of range on line 29. It is a sporadic bug, id say about 50% of the time it comes up. Here is the code:

import random#class constructor for cards
class card:def __init__(self, suit, card_name, card_value):self.suit = suitself.card_name = card_nameself.card_value = card_value#class constructor for the deck
class deck:def __init__(self):self.current_deck = []self.suits = ['hearts', 'diamonds','spades','clubs']self.cards = ['ace','2','3','4','5','6','7','8','9','10','jack','queen','king']def initialize(self):for i in range(len(self.suits)):for j in range(len(self.cards)):if (self.cards[j]=='2' or self.cards[j]=='3' or self.cards[j]=='4' or self.cards[j]=='5' or self.cards[j]=='6' or self.cards[j]=='7' or self.cards[j]=='8' or self.cards[j]=='9'):self.current_deck.append(card(self.suits[i], self.cards[j], int(self.cards[j])))elif (self.cards[j]=='10' or self.cards[j]=='jack' or self.cards[j]=='queen' or self.cards[j]=='king'):   self.current_deck.append(card(self.suits[i], self.cards[j], 10))else:self.current_deck.append(card(self.suits[i], self.cards[j], 11))def shuffle(self):for card in self.current_deck:j = random.randint(0, len(playing_deck.current_deck))temp = cardcard = self.current_deck[j]self.current_deck[j] = tempclass dealer:def __init__(self):self.money = 10000self.hand = []def hit(self, deck_):self.hand.append(deck_.pop())def deal(self, deck_, player_):self.hand.append(deck_.pop())class player: def __init__(self, name):self.name = nameself.money = 200self.hand = []def hit(self, deck_):self.hand.append(deck_.pop())josh = player('josh')playing_deck = deck()playing_deck.initialize()
playing_deck.shuffle()josh.hit(playing_deck.current_deck)for i in range(len(playing_deck.current_deck)):print(vars(playing_deck.current_deck[i]))

You're calling randint:

Return a random integer N such that a <= N <= b. Alias for randrange(a, b+1).

If it's not obvious why this is a problem, let's use a much smaller example:

>>> a = ['x', 'y']
>>> len(a)
2
>>> a[0]
'x'
>>> a[1]
'y'
>>> a[2]
IndexError: list index out of range
>>> randint(0, 2)
1
>>> randint(0, 2)
2 # oops

This is why Python usually uses half-open ranges, where a <= N < b, instead of a <= N <= b. And why you normally want to use randrange instead of randint.

Or, even more often, when you find yourself reaching for randint or randrange, there's a good chance you wanted shuffle (which will randomly reorder the whole list in one go), or choice (which will pick a value out of a list, without needing to first pick an index), etc., so skim through the docs to see if what you want is already written.