Python 2.7超市购物程序：购物车存储方案技术咨询

Hey there! Let’s break down the best way to store your supermarket shopping cart items (name, quantity, price) based on your Python 2.7 code.

Quick Comparison: List vs Dict #

Let’s weigh the pros and cons of each structure for your use case:

Using a List #

A list would store each cart item as a separate entry (like a dictionary or tuple), for example:

cart = [
    {'name': 'asparagus', 'quantity': 2, 'price': 5},
    {'name': 'broccoli', 'quantity': 1, 'price': 6}
]

• Pros: Maintains the exact order items were added, which can be nice for displaying the cart just as the user selected.
• Cons: To update an existing item (like adding more of the same product), you have to loop through the entire list to find a matching name. This gets slower as the cart grows and adds extra code overhead.

Using a Dict #

A dict uses the product name as the key, with the value storing quantity and price (either as a list or another dict):

# Option 1: Value as a list [quantity, price]
cart = {'asparagus': [2, 5], 'broccoli': [1, 6]}

# Option 2: Value as a dict (more readable)
cart = {
    'asparagus': {'quantity': 2, 'price': 5},
    'broccoli': {'quantity': 1, 'price': 6}
}

• Pros:
  • Instantly look up or update any item by its name (no looping required)—perfect for when a user adds the same product multiple times.
  • Cleaner, more efficient code for common cart tasks (updating quantity, checking if an item is already in the cart).
• Cons: Regular dicts in Python 2.7 don’t preserve insertion order. If order matters for displaying the cart, use collections.OrderedDict instead—it works like a dict but keeps track of the order items were added.

Recommendation: Use a Dict (or OrderedDict for Order) #

For your supermarket program, a dict is the better choice. Here’s why:

• You’ll frequently need to check if a product is already in the cart (to update quantity instead of adding duplicates).
• Looking up items by name is far faster with a dict than a list.
• If you want to preserve the order items were added, OrderedDict is a simple drop-in replacement that keeps your cart user-friendly.

Modified Code Example #

Let’s adjust your existing code to implement an OrderedDict-based cart (with stock checks and cart display logic added):

from collections import OrderedDict

inventory={'asparagus':[10,5],'broccoli':[15,6],'carrots':[18,7], 'apples':[20,5],'banana':[10,8],'berries':[30,3], 'eggs':[50,2],'mixed fruit juice':[0,8],'fish sticks':[25,12], 'ice cream':[32,6], 'apple juice':[40,7], 'orange juice':[30,8], 'grape juice':[10,9]}
menu_list=["1. Search for the product", "2. See the basket","3. Check Out","4. Logout","5. Exit"]
cart = OrderedDict()  # Use regular dict if order doesn't matter: cart = {}

def return_to_main():
    print("\n=== Main Menu ===")
    for i in menu_list:
        print(i)
    main_menu = raw_input("Please choose one of the following services: ")
    
    if main_menu == "1":
        select = raw_input("Search for the product: ").lower()
        digit = 1
        found_items = []
        # Collect and display matching products
        for food in inventory:
            if select in food.lower():
                found_items.append(food)
                print(f"{digit}. {food} | Stock: {inventory[food][0]} | Price: ${inventory[food][1]}")
                digit += 1
        
        if found_items:
            # Let user select which item to add
            choice = raw_input("Enter the number of the product to add to cart: ")
            if choice.isdigit() and 1 <= int(choice) <= len(found_items):
                selected_food = found_items[int(choice)-1]
                # Check stock availability
                if inventory[selected_food][0] == 0:
                    print("Sorry, this item is out of stock!")
                else:
                    quantity = raw_input("Enter quantity to buy: ")
                    if quantity.isdigit() and int(quantity) > 0 and int(quantity) <= inventory[selected_food][0]:
                        qty = int(quantity)
                        price = inventory[selected_food][1]
                        # Update cart (add new item or increment quantity)
                        if selected_food in cart:
                            cart[selected_food]['quantity'] += qty
                        else:
                            cart[selected_food] = {'quantity': qty, 'price': price}
                        print(f"Added {qty} {selected_food} to your cart!")
                    else:
                        print("Invalid quantity, or not enough stock available.")
            else:
                print("Invalid selection—please enter a number from the list.")
        else:
            print("No products found matching your search.")
    
    elif main_menu == "2":
        # Display the basket with totals
        if not cart:
            print("Your basket is empty!")
        else:
            print("\n=== Your Basket ===")
            total = 0
            for item, details in cart.items():
                subtotal = details['quantity'] * details['price']
                total += subtotal
                print(f"- {item}: {details['quantity']} x ${details['price']} = ${subtotal}")
            print(f"Total: ${total}")
    
    elif main_menu == "5":
        print("Exiting program. Thanks for shopping!")
        return  # Exit the loop
    else:
        print("Invalid option—please try again.")
    
    return_to_main()  # Loop back to main menu

# Start the program
return_to_main()

Key Improvements #

• Uses OrderedDict to preserve the order items were added (optional but user-friendly).
• Checks stock availability before allowing quantity selection.
• Updates existing cart items instead of adding duplicates.
• Displays the cart with subtotals and a grand total for checkout clarity.

内容的提问来源于stack exchange，提问作者Marshall Alife