Python3中如何将输入与字典元素匹配？新手购物清单实现求助

Hey there! Let's work through this shopping list problem step by step. I see you're stuck on matching input items to their prices in the dictionary, plus there are a few syntax and logic gaps we can iron out to get this working right.

First, Let's Fix Syntax & Naming Issues #

First off, a couple quick fixes to avoid Python errors:

• Don't use list as a variable name—it's a built-in Python type! Let's rename that to item_prices instead.
• If needs to be lowercase (if) in Python (case matters here!).
• Your input() call is missing a closing parenthesis—easy typo to fix!
• sum is also a built-in function, so let's use total_cost for our running total to avoid confusion.
• You'll need to define a budget value (since your logic references it) and initialize total_cost to 0 at the start.

Matching Items to Their Prices #

The key part you're missing: to get the price of the item the user inputs, you just use item_prices[buy]—this looks up the value (price) associated with the key (item name) in your dictionary. Super straightforward once you know the syntax!

Updated Working Code #

Here's a revised version of your function that puts it all together, with comments explaining each step:

def shoplist():
    # Define your item prices (renamed from "list" to avoid conflict)
    item_prices = {"apple": 30, "orange": 20, "milk": 60}
    # Set your budget (you can change this to any number that makes sense)
    budget = 100
    # Initialize total cost to 0 before we start adding items
    total_cost = 0

    while total_cost <= budget:
        # Get user input, with the missing closing parenthesis added
        buy = str(input("What do you want to purchase? (Type 'quit' to stop early) "))
        
        # Let the user exit early if they're done shopping
        if buy.lower() == "quit":
            break
        
        # Check if the item exists in our price dictionary
        if buy in item_prices:
            # Grab the item's price and add it to the total (this is the matching step you needed!)
            item_price = item_prices[buy]
            total_cost += item_price
            print(f"Added {buy} for {item_price}. Total so far: {total_cost}")
        else:
            print(f"Sorry, we don't have {buy} in our inventory.")
    
    # Once we exit the loop, explain why to the user
    if total_cost > budget:
        print(f"Whoa, your total ({total_cost}) is over your budget of {budget}! Stopping here.")
    else:
        print(f"Thanks for shopping! Your final total is {total_cost}.")

# Call the function to run the program
shoplist()

Key Improvements Explained #

• Added an early quit option so the user can stop shopping before hitting the budget.
• Prints the running total every time an item is added, so the user can track their spending.
• Gives a clear message if the user inputs an item that isn't in the dictionary, instead of crashing.
• The loop stops immediately once adding an item would push the total over budget, which aligns with your original goal.

内容的提问来源于stack exchange，提问作者Aimee