Question

我对编码非常陌生，我正在尝试创建一个包含商品和价格的商店列表。也就是说，一旦键入所有项目，该函数应计算总和并在您超出预算时停止。所以我写了类似的东西：

def shoplist():
    list={"apple":30, "orange":20, "milk":60......}
    buy=str(input("What do you want to purchase?")
    If buy in list:
        While sum<=budget:
            sum=sum+??
shoplist ()

我真的不知道如何将项目的输入与列表中的价格相匹配...... 我的第一个想法是使用'if'，但当你在列表中有超过10个项目和随机输入时，这有点不切实际。我迫切需要帮助......所以任何建议都会很好！（或者如果你有一个更好的解决方案，并认为我用这种方式写它是完全垃圾......请让我知道那些更好的解决方案是什么

Answer 1

您发布的代码不会在python中运行。 list是一个内置函数，不应该用于变量名，因为它引用了一个dict对象，所以它会引起双重困惑。 input()已经返回一个str，因此强制转换没有效果。 if和while应该是小写的，并且没有缩进，因此我们无法知道这些语句的限制。

有太多错误，请看一下：

def shoplist(budget):
    prices = {"apple":30, "orange":20, "milk":60}

    # Initialise sum
    sum = 0

    while sum <= budget:
        buy = input("What do you want to purchase?")

        # Break out of the loop if the user hts <RETURN>
        if not buy: break

        if buy in prices:
            sum += prices[buy]   # This gets the price
        else:
            print("Invalid item", buy)

shoplist(142)

那我改变了什么？预算必须来自某个地方，所以我把它作为一个参数传递（142，我做了这个）。我将总和初始化为零，然后将while循环移到外面。

注意很多空格 - 它使代码更容易阅读，对性能没有影响。

要做出很多改进。应向用户显示可能的项目和价格列表，以及每次购买剩余的预算。另请注意，可以超出预算，因为我们可能只有30个预算，但我们仍然可以购买牛奶（60个） - 我们需要另一个检查（if声明）在那里！

我会把改进留给你。玩得开心！

Answer 2

以此为例：

# this is a dictionary not a list
# be careful not using python reserved names as variable names
groceries = {
    "apple":30, 
    "orange":20, 
    "milk":60
}

expenses = 0
budget = 100
cart = []
# while statements, as well as if statements are in lower letter
while expenses < budget:
    # input always returns str, no need to cast
    user_input = input("What do you want to purchase?")
    if user_input not in groceries.keys():
        print(f'{user_input} is not available!')
        continue
    if groceries[user_input] > budget - expenses:
        print('You do not have enough budget to buy this')
        user_input = input("Are you done shopping?Type 'y' if you are.")
        if user_input == 'y':
            break
        continue
    cart.append(user_input)
    # this is how you add a number to anotherone
    expenses += groceries[user_input]
print("Shopping cart full. You bought {} items and have {} left in your budget.".format(len(cart), budget-expenses))

Answer 3

我已对您的代码进行了一些更改以使其正常工作，并解释说明包括使用#符号指示的注释。

最重要的两件事是所有括号都需要关闭：

fun((x, y)  # broken
fun((x, y)) # not broken

和Python中的关键字都是小写的：

if, while, for, not # will work
If, While, For, Not # won't work

您可能会对True和False感到困惑，这可能应该是小写的。他们已经这么久了，现在改变它们为时已晚。

budget = 100 # You need to initialize variables before using them.

def shoplist():
    prices = {         # I re-named the price list from list to prices
        'apple'  : 30, # because list is a reserved keyword. You should only
        'orange' : 20, # use the list keyword to initialize list objects.
        'milk'   : 60, # This type of object is called a dictionary.
    } # The dots .... would have caused an error.
    # In most programming languages, you need to close all braces ().
    # I've renamed buy to item to make it clearer what that variable represents.
    item = input('What do you want to purchase? ')
    # Also, you don't need to cast the value of input to str; 
    # it's already a str.
    if item in prices:
        # If you need an int, you do have to cast from string to int.
        count = int(input('How many? ')) 
        cost = count*prices[item] # Access dictionary items using [].
        if cost > budget:
            print('You can\'t afford that many!')
        else:
            # You can put data into strings using the % symbol like so:
            print('That\'ll be %i.' % cost) # Here %i indicates an int.
    else:
        print('We don\'t have %s in stock.' % item) # Here %s means str.

shoplist()

许多初学者在StackOverflow上发布了破坏的代码而没有说他们会得到错误或者错误是什么。发布错误消息总是有帮助的。如果您有更多问题，请与我们联系。

如何在Python3

3 个答案: