Question about deck of cards using OOP python - python-3.x

Question

This is the current code:
import random
class Cards():
def __init__(self, value, suit):
self.value = value
self.suit = suit
def show(self):
print("{} of {}".format(self.value, self.suit.upper()))
class Deck():
def __init__(self):
self.cards = []
self.build()
def build(self):
suits = ['Spades', 'Hearts', 'Clubs', 'Diamonds']
for suit in suits:
for value in range(1,14):
self.cards.append(Cards(value,suit))
def show(self):
for card in self.cards:
card.show()
def shuffle(self):
for i in range(len(self.cards)-1, 0, -1):
rand = random.randint(0, i)
self.cards[i], self.cards[rand] = self.cards[rand], self.cards[i]
def draw(self):
return self.cards.pop()
deck = Deck()
deck.shuffle()
deck.draw().show()
The OOP part still confuses me, so excuse my elementary question but how come I can do deck.draw().show() but not deck.shuffle().draw().show()?
What I mean is that when I keep deck.shuffle() AND THEN do deck.draw().show() it returns to me random cards. So what if I just wanted to do deck.shuffle().draw().show()? Why does it give me an error of
Traceback (most recent call last):
File "c:\Users\Desktop\deckofcards.py", line 40, in <module>
deck.shuffle().draw().show()
AttributeError: 'NoneType' object has no attribute 'draw'
PS C:\Users\learning_log>

Answer 1

You can get that behaviour with one small change:
def shuffle(self):
for i in range(len(self.cards)-1, 0, -1):
rand = random.randint(0, i)
self.cards[i], self.cards[rand] = self.cards[rand], self.cards[i]
return self # <- return a reference to the deck itself
Demonstration:
In [95]: deck.shuffle().draw().show()
8 of HEARTS
The reason you were getting that error is that you weren't returning anything from shuffle().

Answer 2

You can't do deck.shuffle().draw().show() because as the error says, deck.shuffle() is a nonetype, that means it has no value, because shuffle() does some stuff, it doesn't return anything so you are esentially doing 'nothing'.draw().show(). To solve it you could return something, just like other answer said you could return a reference to the deck.