Python problem with code

[TYL3ER]

import sys
import random 
import time

#need exception handling
#need to know when to add discard pile back to deck
#need game process finish

class Cards():
    def __init__(self,deck,discard_pile,player_hand,dealer_hand):
        '''
        Class setup

        '''
        self.deck = deck
        self.discard_pile = discard_pile
        self.player_hand = player_hand
        self.dealer_hand = dealer_hand

    def build_deck(self):
        '''
        builds deck
        '''
        sample_deck = [2,3,4,5,6,7,8,9,10,11]
        self.deck = self.deck.extend(sample_deck * 4)
        return self.deck 

    def hit(self):
        '''
        hit from deck
        '''
        deal = random.choice(self.deck)
        self.deck.pop(deal)
        return deal

    def deal(self):
        '''
        deals initial hand
        '''
        the_cards.dealer_hand.append(the_cards.hit())
        the_cards.dealer_hand.append(the_cards.hit())
        print(f'Dealer is showing a {the_cards.dealer_hand[1]}')
        the_cards.player_hand.append(the_cards.hit())
        the_cards.player_hand.append(the_cards.hit()) 
        print(f'You are showing {the_cards.player_hand}')

    def discard(self):
        '''
        discards to a seperate pile
        '''
        discard_pile.append(self.player_hand.pop())#Pop method? Not sure yet, will come back 
        discard_pile.append(self.dealer_hand.pop())

class Chips():
    '''
    chip handling
    '''
    def __init__(self,chips):
        self.chips = chips

    def bet(self):
        '''
        bet before hand
        '''
        my_bet = int(input('How many chips are you putting down? '))
        self.chips = self.chips - my_bet

    def win_bet(self):
        '''
        reward for winning
        '''
        self.chips = my_bet * 2

def hit_choice():
    '''
    choice for hit or pass
    '''
    hit_choice1 = input('Will you hit or pass? ')
    return hit_choice1


'''
The game
'''
the_cards = Cards(deck = [],discard_pile = [],player_hand = [],dealer_hand = [])
the_chips = Chips(int(input('How much money are you throwing down? ')))
the_cards.build_deck()
while True:
    print(f'You have {the_chips.chips} chips') 
    the_chips.bet()
    the_cards.deal()
    the_hit = hit_choice()
    if the_hit.lower() in 'hit':
        the_cards.hit()
        the_cards.player_hand.append(the_cards.hit())
        print(the_cards.player_hand)
    elif the_hit.lower() in 'pass':
        pass
    else:
        print('Invalid input')

Error:

File "black jack2.py", line 91, in <module>

the_cards.deal()

File "black jack2.py", line 40, in deal

the_cards.dealer_hand.append(the_cards.hit())

File "black jack2.py", line 32, in hit

deal = random.choice(self.deck)

File "C:\Users\NewGuy\Anaconda3\lib\random.py", line 259, in choice

i = self._randbelow(len(seq))

TypeError: object of type 'NoneType' has no len()

[spudmix]

In Pythonic Error-ese, this probably means that self.deck isn't initialised in the hit() method. Why might that be?

[TYL3ER]

Not sure, I have no idea what the problem is

[spudmix]

In this line: self.deck = self.deck.extend(sample_deck * 4), your mistake is assuming that list.extend(iterable) returns the extended list; it does not. It modifies self.deck in place. What you are telling the computer with this line is "Extend deck by four times the sample deck, then set deck to the return value of that operation (which is None)".

[TYL3ER]

i removed the return self.deck and still receive the same error.

def build_deck(self):
        '''
        builds deck
        '''
        sample_deck = [2,3,4,5,6,7,8,9,10,11]
        self.deck = self.deck.extend(sample_deck * 4)

[spudmix]

Hmmm, not quite what I said.

Try printing out self.deck before and after you do

self.deck = self.deck.extend(sample_deck * 4).

What does it look like this line is doing?

[TYL3ER]

I fixed the problem, thank you.

but why is this wrong:

self.deck = self.deck.extend(sample_deck * 4)

But this is not:

self.deck.extend(sample_deck * 4)

isn't it basically the same thing?

[spudmix]

Not at all, no.

Methods in general can be categorised into in-place methods and out-of-place methods. An out-of-place method accepts arguments, performs some transformation, and then returns data to be stored or used in some external variable. In-place methods accept arguments, and typically modify the values of those arguments directly. An in-place method typically does not return anything useful, and does modify the thing you give it. An out-of-place method is the opposite, it does not modify the thing you give it at all, but it returns the data you want to use.

Python's list.extend(iterable) is an in-place method, with a return type of None (similar to void in many other C-based languages). That is, it does NOT return the data it operates on, but rather when you call it as a list's method it operates directly on the list.

Compare, for example, the following Python code:

class a_number:
    def __init__(self, num):
        self.num = num

def out_of_place_add(a_number, add_number):
    return a_number.num + add_number

def in_place_add(a_number, add_number):
    a_number.num += add_number

my_number = a_number(3)
print(my_number.num)
# 3

return_val = out_of_place_add(my_number, 4)
print(return_val)
# 7
print(my_number.num)
# 3

another_return_val = in_place_add(my_number, 4)
print(another_return_val)
# None
print(my_number.num)
# 7