Python习题 175：定义类实现购物车的操作

class Item:
    def __init__(self, name: str, price: float):
        self.name = name
        self.price = price

class ShoppingCart:
    def __init__(self):
        self.cart = {}

    def add_item(self, item: Item, quantity: int = 1) -> None:
        """
        Add items to the shopping cart.

        Args:
        - item (Item): The item to be added.
        - quantity (int): The quantity of the item. Default is 1.

        Returns:
        - None
        """
        self.cart[item.name] = {"price": item.price, "quantity": self.cart.get(item.name, {}).get("quantity", 0) + quantity}

    def remove_item(self, item: Item, quantity: int = 1) -> None:
        """
        Remove items from the shopping cart.

        Args:
        - item (Item): The item to be removed.
        - quantity (int): The quantity of the item to be removed. Default is 1.

        Returns:
        - None
        """
        if item.name in self.cart:
            self.cart[item.name]["quantity"] = max(0, self.cart[item.name]["quantity"] - quantity)
            if self.cart[item.name]["quantity"] == 0:
                del self.cart[item.name]

    def calculate_total(self) -> float:
        """
        Calculate the total cost of items in the shopping cart.

        Returns:
        - float: The total cost.
        """
        return sum(item["price"] * item["quantity"] for item in self.cart.values())

    def clear_cart(self) -> None:
        """
        Clear all items from the shopping cart.

        Returns:
        - None
        """
        self.cart = {}

    def checkout(self) -> None:
        """
        Simulate the checkout process.

        Returns:
        - None
        """
        total_cost = self.calculate_total()
        print(f"Total cost of items in the cart: ${total_cost:.2f}")

        confirmation = input("Confirm purchase? (yes/no): ").lower()
        if confirmation == "yes":
            print("Payment successful! Thank you for your purchase.")
            self.clear_cart()
        else:
            print("Purchase canceled.")

    def __str__(self) -> str:
        """
        Return a string representation of the shopping cart.

        Returns:
        - str: String representation of the shopping cart data.
        """
        return str(self.cart)

# Example usage:
laptop = Item(name="Laptop", price=800.0)
mouse = Item(name="Mouse", price=20.0)
monitor = Item(name="Monitor", price=300.0)

cart = ShoppingCart()

cart.add_item(item=laptop, quantity=2)
cart.add_item(item=mouse, quantity=5)
cart.add_item(item=monitor, quantity=1)

print("Cart data before checkout:", cart)
print('Cart total:', cart.calculate_total())
cart.checkout()

# Verify the cart is cleared after checkout
print("Cart data after checkout:", cart)