如何检查 Python 中的成本是否低于零

Question

作为我 class 中的一项最终任务，我们的任务是编写一款可以在游乐园排队玩的游戏。完成游戏后，我们需要让玩家有机会购买一定数量的 6 种不同的奖品，只要他们有足够的积分即可。

在我的程序中，如果有人订购了一定数量的奖品，超过了他们的平均分，它会告诉你你没有足够的积分来买它，你需要重新输入你的回答。

但是，我犯了一个错误，即使发送到程序中的数字小于所说的余额，玩家的余额（他们所有点数的总和）仍低于零。我觉得这和每个奖品的成本有关，因为其中一个木蛇值35分，其他的也一样，只是数字不同。

balance = 100

#How many glowsticks the player wants
        prize1 = int(input("Tell me again how many glowsticks you want "))
        if prize1 <= balance:
            prize1 = prize1 * 10
            balance = balance - prize1
            print("Your balance is now",balance,"points.")
        elif prize1 > balance:
            print("Too many glowsticks, please change your amount")
            break
        
        #Confirm again if that's how many jumbo glasses the player wanted
        prize2 = int(input("Tell me again how many jumbo glasses you want "))
        if prize2 <= balance:
            prize2 = prize2 * 15
            balance = balance - prize2
            print("Your balance is now",balance,"points.")
        elif prize2 > balance:
            print("Too many jumbo glasses, please change your amount.")
            break
        
        #How many inflatable hammers the player wants
        prize1 = int(input("Tell me again how many inflatable hammers you want "))
        if prize1 <= balance:
            prize1 = prize1 * 25
            balance = balance - prize1
            print("Your balance is now",balance,"points.")
        elif prize1 > balance:
            print("Too many inflatable hammers, please change your amount")
            break
        
        #How many of dinosaur grabbers the player wants
        prize2 = int(input("Tell me again how many dinosaur grabbers you want "))
        if prize2 <= balance:
            prize2 = prize2 * 30
            balance = balance - prize2
            print("Your balance is now",balance,"points.")
        elif prize2 > balance:
            print("Too many dinosaur grabbers, please change your amount.")
            break
        
        #How many wooden snakes the player wants
        prize1 = int(input("Tell me again how many wooden snakes you want "))
        if prize1 <= balance:
            prize1 = prize1 * 35
            balance = balance - prize1
            print("Your balance is now",balance,"points.")
        elif prize1 > balance:
            print("Too many wooden snakes, please change your amount")
            break
        
        #How many foam swords the player wants
        prize2 = int(input("Tell me again how many foam swords you want "))
        if prize2 <= balance:
            prize2 = prize2 * 40
            balance = balance - prize2
            print("Your balance is now",balance,"points.")
        elif prize2 > balance:
            print("Too many foam swords, please change your amount.")
            break

这是我的代码中出现问题的部分。我想让玩家在获胜后输入他们想要的每个奖品的数量。如果他们负担不起他们想要的金额，因为这会导致您的余额低于零，或者超过您的余额，程序会要求您更改金额以适应它。

P.S。本例中余额为 100 的原因是出于演示目的。它可能并不总是等于该数字，并且可能更高或更低，具体取决于玩家在整个游戏中的表现。

Answer 1

编程中有一条关键规则叫做 DRY：不要重复自己。请注意此架构如何用更少的代码解决问题。它使添加新项目变得容易，如果你想出更好的方法来处理事情，一个修复就可以解决所有问题：

balance = 100

options = [
    ('glowsticks', 10),
    ('jumbo glasses', 15),
    ('inflatable hammers', 25),
    ('dinosaur grabbers', 30),
    ('wooden snakes',35),
    ('foam swords', 40)
]

for name, cost in options:
    while True:
        count = int(input(f"Tell me again how many {name} you want? "))
        if count * cost <= balance:
            balance -= count * cost
            print( "Your balance is now", balance, "points.")
            break
        else:
            print(f"Too many {name}, please change your amount")

Answer 2

编辑

根据@Tim 的反馈，这不是递归的好用法，我更新了我的代码，使用相同的基本思想。

问题在于，在您的输入中，您是在比较项目的数量与积分的余额，而不是将他们想要的数量与可用数量的成本进行比较。

为了尽量减少代码行数，您还可以创建一个递归函数，在数字无效时继续请求输入。我建议如下：

balance = 100

prices  = {'glowsticks':10, #etc}

def check_balance(item, qty):
    global balance 
    while (cost := prices[item] * qty) > balance:
        qty = int(input("Too many, try again: "))
    else:
        balance -= cost
        print(f"New balance is {balance}.")
        return

Answer 3

假设n是你想买的木蛇的数量

你在检查余额是否小于n（所以如果我想要2条蛇，只要余额大于等于2，它就会让我买木蛇）但是你需要检查购买n条蛇的成本是否小于余额。

这当然适用于您计划中的所有项目。

您也可以将 elif 语句替换为 else 语句，就好像成本不低于或等于余额一样，您无需检查就可以确定它会更大。

我以木蛇为例

替换

    #How many wooden snakes the player wants
    prize1 = int(input("Tell me again how many wooden snakes you want "))
    if prize1 <= balance:
        #buy the item
    elif prize1 > balance:
        print("Too many wooden snakes, please change your amount")
        break

和

    #How many wooden snakes the player wants
    prize1 = int(input("Tell me again how many wooden snakes you want "))
    if prize1 * 35 <= balance:
        #buy the items
    else:
        print("Too many wooden snakes, please change your amount")

如何检查 Python 中的成本是否低于零

How to Check if Costs go Below Zero in Python

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currency

编辑