Métodos mágicos de contenedores

Parte de la sección Object Oriented Programming del Journey de Python de Coddy — lección 35 de 64.

Los métodos mágicos de contenedor permiten que sus clases se comporten como contenedores integrados (listas, diccionarios, etc.). Permiten la indexación, la comprobación de longitud y la iteración en sus objetos personalizados.

Aquí hay un ejemplo de una clase con métodos mágicos de contenedor:

class CustomList:
    def __init__(self, items):
        self.items = items
    
    def __len__(self):
        return len(self.items)
    
    def __getitem__(self, index):
        return self.items[index]
    
    def __setitem__(self, index, value):
        self.items[index] = value
    
    def __iter__(self):
        return iter(self.items)
    
    def __contains__(self, item):
        return item in self.items

El método __len__ hace que len() funcione:

my_list = CustomList([1, 2, 3, 4])
print(len(my_list))  # 4

El método __getitem__ permite la indexación para la recuperación:

print(my_list[2])    # 3
print(my_list[0])    # 1

El método __setitem__ permite la indexación para la asignación:

my_list[1] = 10
print(my_list[1])    # 10

El método __contains__ hace que el operador in funcione:

print(3 in my_list)     # True
print(100 in my_list)   # False

El método __iter__ permite la iteración:

for item in my_list:
    print(item)

Salida:

4
3
1
10
True
False
1
10
3
4

Punto clave: Los métodos mágicos de contenedor como __len__, __getitem__, __setitem__, __iter__ y __contains__ hacen que tus clases personalizadas se comporten como contenedores integrados. Esto proporciona indexación, iteración y pruebas de pertenencia intuitivas para tus objetos.

Desafío

Intermedio

En este desafío, implementarás una clase Deck que simula una baraja de cartas con una funcionalidad completa y siguiendo las convenciones adecuadas de Python.

Solo necesitas editar el archivo deck.py. Sigue los comentarios TODO en el código que te guiarán para implementar:

Una inicialización estándar de una baraja de 52 cartas (usando cadenas como "2H", "KD", "AS")
Soporte para las operaciones integradas de Python:
- Indexación (deck[0])
- Comprobación de longitud (len(deck))
- Iteración (for card in deck)
- Prueba de pertenencia ("AS" in deck)
Un método shuffle para aleatorizar el orden de las cartas

Pruébalo tú mismo

from deck import Deck

# Manejador de casos de prueba exhaustivo
test_case = input()

def test_basic_functionality():
    deck = Deck()
    assert len(deck) == 52, f"Deck should have 52 cards, but has {len(deck)}"
    
    first_card = deck[0]
    assert isinstance(first_card, str), f"Card should be a string, but got {type(first_card)}"
    
    assert "AS" in deck, "Ace of Spades should be in the deck"
    assert "XY" not in deck, "XY is not a valid card and should not be in the deck"
    
    cards = [card for card in deck]
    assert len(cards) == 52, f"Iteration should yield 52 cards, but got {len(cards)}"
    
    original_first_five = [deck[i] for i in range(5)]
    deck.shuffle()
    shuffled_first_five = [deck[i] for i in range(5)]
    assert original_first_five != shuffled_first_five or len(deck) <= 5, "Shuffle should change card order"
    
    print("Basic functionality tests passed!")

def test_edge_cases():
    deck = Deck()
    
    # Probar el acceso a la primera y última carta
    first_card = deck[0]
    last_card = deck[51]
    assert isinstance(first_card, str) and isinstance(last_card, str), "First and last cards should be strings"
    
    # Probar indexación negativa
    assert deck[-1] == deck[51], "Negative indexing should work correctly"
    
    # Probar acceso fuera de los límites
    try:
        invalid_card = deck[52]
        print("Test failed: Should raise IndexError for out of bounds access")
    except IndexError:
        print("Edge case test passed: IndexError raised for out of bounds access")
    
    print("Edge case tests passed!")

def test_card_uniqueness():
    deck = Deck()
    cards = [card for card in deck]
    unique_cards = set(cards)
    
    assert len(unique_cards) == 52, f"All cards should be unique, but found {len(unique_cards)} unique cards"
    
    # Verificar que existen cartas específicas
    expected_cards = ["2H", "10S", "KD", "AC"]
    for card in expected_cards:
        assert card in deck, f"Expected card {card} not found in deck"
    
    print("Card uniqueness tests passed!")

def test_shuffle_behavior():
    deck = Deck()
    original_order = [card for card in deck]
    
    # Primer barajado
    deck.shuffle()
    first_shuffle = [card for card in deck]
    assert len(first_shuffle) == 52, "Shuffle should preserve all 52 cards"
    assert set(first_shuffle) == set(original_order), "Shuffle should not add or remove cards"
    
    # Lo más probable es que el orden haya cambiado (aunque hay una probabilidad minúscula de que no sea así)
    different_order = (original_order != first_shuffle)
    
    # Segundo barajado para estar extra seguros
    deck.shuffle()
    second_shuffle = [card for card in deck]
    different_order_2 = (first_shuffle != second_shuffle)
    
    assert different_order or different_order_2, "Multiple shuffles should change the order"
    
    print("Shuffle behavior tests passed!")

def test_contains_behavior():
    deck = Deck()
    
    # Probar que todas las cartas válidas están en el mazo
    suits = ['H', 'D', 'C', 'S']
    ranks = ['2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A']
    
    for suit in suits:
        for rank in ranks:
            card = rank + suit
            assert card in deck, f"Valid card {card} should be in the deck"
    
    # Probar que las cartas inválidas no están en el mazo
    invalid_cards = ["1H", "11S", "XD", "AX", "JX", ""]
    for card in invalid_cards:
        assert card not in deck, f"Invalid card {card} should not be in the deck"
    
    print("Contains behavior tests passed!")

def test_iteration_behavior():
    deck = Deck()
    
    # Probar iteración
    card_count = 0
    for card in deck:
        card_count += 1
        assert isinstance(card, str), f"Each card should be a string, but got {type(card)}"
    
    assert card_count == 52, f"Iteration should yield 52 cards, but got {card_count}"
    
    # Probar múltiples iteraciones
    first_iteration = [card for card in deck]
    second_iteration = [card for card in deck]
    assert first_iteration == second_iteration, "Multiple iterations should yield the same order"
    
    print("Iteration behavior tests passed!")

# Ejecutar la prueba apropiada basada en la entrada
if test_case == "basic_functionality":
    test_basic_functionality()
elif test_case == "edge_cases":
    test_edge_cases()
elif test_case == "card_uniqueness":
    test_card_uniqueness()
elif test_case == "shuffle_behavior":
    test_shuffle_behavior()
elif test_case == "contains_behavior":
    test_contains_behavior()
elif test_case == "iteration_behavior":
    test_iteration_behavior()
else:
    # Prueba por defecto - ejecutar la suite de pruebas original
    def test_deck():
        try:
            # Probar inicialización y longitud
            deck = Deck()
            assert len(deck) == 52, f"Deck should have 52 cards, but has {len(deck)}"
            
            # Probar getitem
            first_card = deck[0]
            assert isinstance(first_card, str), f"Card should be a string, but got {type(first_card)}"
            
            # Probar contains
            assert "AS" in deck, "Ace of Spades should be in the deck"
            assert "XY" not in deck, "XY is not a valid card and should not be in the deck"
            
            # Probar iteración
            cards = [card for card in deck]
            assert len(cards) == 52, f"Iteration should yield 52 cards, but got {len(cards)}"
            assert len(set(cards)) == 52, "All cards in the deck should be unique"
            
            # Probar barajado (comprobación básica de que el orden cambia)
            original_first_five = [deck[i] for i in range(5)]
            deck.shuffle()
            shuffled_first_five = [deck[i] for i in range(5)]
            assert original_first_five != shuffled_first_five or len(deck) <= 5, "Shuffle should change card order"
            
            # Comprobar que el barajado no pierde cartas
            assert len(deck) == 52, f"Deck should still have 52 cards after shuffle, but has {len(deck)}"
            
            print("All tests passed!")
        except AssertionError as e:
            print(f"Test failed: {e}")

    test_deck()
    print("Tests completed")