Python报错：can't multiply sequence by non-int of type 'float'问题求助

我是Python新手，受该问题困扰已一周。运行咖啡订单程序时出现报错：can't multiply sequence by non-int of type 'float'，卡在计算总价的部分，恳请帮忙解决。

原代码 #

price = {
    "Espresso": 5.80,
    "Americano": 6.90,
}

currency = "$"

print ("welcome coffee machine!\t")
name = input ("can i get your name?\n")

print ("what do you like to order mr/ms " + name + "\n"  )


menu = ("Espresso, Americano")

print (menu)
menu = (input())


quantity = input("How many " + menu + " would you like?\n")
quantity = str(input())

#im stuck at here! T_T 
if menu == "Espresso" :
    price = 5.80
    total = quantity * price
    quantity.append(quantity)
    price.append(price)
    print(total)

elif menu == "Americano":
    price = 6.90
    total = quantity * price
    quantity.append(quantity)
    price.append(price)
    print(total)

else:
     menu()

#invoice receipt

print("Thank you for order " + name + ", please wait your " + menu + " at counter\n")

错误原因分析 #

• 数量类型错误：你把quantity转成了字符串（str(input())），字符串和浮点数（价格）相乘会触发报错——Python仅允许字符串和整数相乘（作用是重复字符串），和浮点数相乘无意义，所以报错。
• 重复获取输入：连续两次调用input()获取数量，第一次的输入被直接覆盖，完全没必要。
• 错误调用列表方法：append()是列表的方法，但quantity是字符串，不能调用这个方法；且逻辑上也不需要把数量添加到自身，属于错误写法。
• 浪费字典资源：一开始定义了price字典存储饮品价格，但后面又直接给price赋值单个浮点数，完全可以直接用字典取值。
• else分支错误：menu是字符串，不是函数，调用menu()会触发新的报错。

修正后的代码 #

price = {
    "Espresso": 5.80,
    "Americano": 6.90,
}

currency = "$"

print("welcome coffee machine!")
name = input("can i get your name?\n")

print(f"what do you like to order mr/ms {name}\n")

# 更清晰地展示菜单
menu_options = ["Espresso", "Americano"]
print("Available drinks:", ", ".join(menu_options))
menu = input("Please enter your choice: ").strip()

# 获取数量并转为整数，添加输入验证避免无效值
while True:
    try:
        quantity = int(input(f"How many {menu} would you like?\n"))
        if quantity > 0:
            break
        else:
            print("Please enter a positive number.")
    except ValueError:
        print("Invalid input, please enter a number.")

# 计算并输出总价
if menu in price:
    total = quantity * price[menu]
    print(f"Total price: {currency}{total:.2f}")
else:
    print(f"Sorry, {menu} is not on our menu.")

# 结账提示
print(f"Thank you for your order {name}, please wait for your {menu} at the counter.\n")

主要修正点 #

1. 将quantity转为整数类型，确保可以和浮点数价格正常相乘。
2. 移除重复的input()调用，添加输入验证，防止用户输入非数字或负数。
3. 利用price字典直接获取对应饮品的价格，避免重复赋值。
4. 移除错误的append()调用，修正else分支的错误处理逻辑。
5. 使用f-string让字符串拼接更简洁易读。

内容的提问来源于stack exchange，提问作者Merong Shah