Standing choice not doing anything

Question

So I am trying to make a simple blackjack game in python 3 and everything works just fine, except that I can't stand. If I input 2 it won't do anything. Thanks in advance. EDIT 1: Hitting works well. EDIT 2: Posted the entire script, so you can reproduce the problem I'm facing, as @roganjosh suggested.

from random import shuffle
import sys


def deal(deck, player, dealer):
    shuffle(deck)

    for _ in range(2):
        player.append(deck.pop())
        dealer.append(deck.pop())

def score(hand):
    non_aces = [c for c in hand if c != 'A']
    aces = [c for c in hand if c == 'A']

    sum = 0

    for card in non_aces:
        if card in 'JQK':
            sum += 10
        else:
            sum += int(card)

    for card in aces:
        if sum <= 10:
            sum += 11
        else:
            sum += 1

    return sum

def display_info(player, dealer, stand):
    print("Your cards: [{}] ({})".format(']['.join(player), score(player)))
    if stand:
        print("Dealer cards: [{}] ({})".format(']['.join(dealer), score(dealer)))
    else:
        print("Dealer cards: [{}] [?]".format(dealer[0]))

def results(player, dealer, hand, stand):
    if score(player) == 21 and hand:
        print("Blackjack! You won!")    
        sys.exit()    
    elif score(player) > 21:
        print("Busted. You lost!")   
        sys.exit()     
    if stand:
        if score(dealer) > 21:
            print("Dealer busted. You won!")
        elif score(player) > score(dealer):
            print("You beat the dealer! You won!")
        elif score(player) < score(dealer):
            print("You lost!")
        else:
            print("Push. Nobody wins or losses.")
        sys.exit()

def hit_stand(deck, player, dealer, hand, stand):
    print("What would you like to do")
    print("[1] - Hit\n[2] - Stand")
    choice = input("> ")
    hand = False
    if choice == '1':
        player.append(deck.pop())
    elif choice == '2':
        stand = True
        while score(dealer) <= 16:
            dealer.append(deck.pop())

if __name__ == '__main__':
    deck = ['A', '2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K']*4
    player = []
    dealer = []
    standing = False
    first_hand = True
    deal(deck, player, dealer)
    while True:
        display_info(player, dealer, standing)
        results(player, dealer, first_hand, standing)
        hit_stand(deck, player, dealer, first_hand, standing)

Answer 1

You are not checking the result after the player chooses to stand. Since you only deal() once before the while True loop, you just get an infinite condition if you choose to stand repeatedly. Calculate the score after the dealer has drawn all their cards.

def hit_stand(deck, player, dealer, hand, stand):
    print("What would you like to do")
    print("[1] - Hit\n[2] - Stand")
    choice = input("> ")
    hand = False
    if choice == '1':
        player.append(deck.pop())
    elif choice == '2':
        stand = True
        while score(dealer) <= 16:
            print(score(dealer))
            dealer.append(deck.pop())
        display_info(player, dealer, stand)
        results(player, dealer, first_hand, stand) # HERE

On a somewhat unrelated note, crashing out of the game after the final score is determined is not very elegant. You will want to look at a better construct than while True: and sys.exit() to control flow, but that's an exercise for you.

Finally, you should not be using sum as a variable name inside score() because this is a built-in function that you're redefining. Use something like total so that you don't risk masking the built-in function itself.

Answer 2

The answer from @roganjosh is correct, but I wanted to add another note because I think it's a really important point about how Python works. It's something that people who came from a background in C/C++/Java (i.e. pretty much all of us) need to un-learn when using Python.

As I stated in the comments above, in the original code from Maria Laura, it looks like the call to hit_stand is intended to use some variables (such as stand) as output variables, and in Python we cannot have "output variables" in a function call. But Maria Laura mentioned that "hitting works well", which means that the parameter player was getting modified. So, if we cannot have "output variables", then why was the value of player getting modified by the function hit_stand?

When the code calls hit_stand, five objects are passed in to the function:

• A list object, which is given the name deck,
• A list object, which is given the name player,
• A list object, which is given the name dealer,
• A Boolean object, which is given the name hand,
• A Boolean object, which is given the name stand

The code outside this function also has names (deck, player, dealer, first_hand, standing) pointing to these same five objects. Within the code of hit_stand the .append() method is called on the player and dealer list objects, and the .pop() method is called on the deck object, so all those objects are mutated. The names from the calling scope still point to those same objects, so those names will now see those changes.

The story for hand and stand is different. Inside the hit_stand function, hand and stand are assigned new values with the = operator. As outlined in this excellent write-up from Fredrik Lundh, the = operator in Python does not "change" a variable, it just takes an object and binds it to a name. The objects themselves did not change, rather they were replaced with new Boolean objects. So the variable standing in the outer scope is still pointing to its original Boolean object, and the variable stand within the function is pointing to a brand-new Boolean object, different from the one in the outer scope. There is nothing we can do to the variables hand and stand which will be seen in the outside scope, there cannot be such thing as "pass by reference" or "output parameter" like we have in other languages.

It's a concept that can seem very foreign at first, until we un-learn what we have learned in our C/C++/Java education.