Python:自动售货机

Question

该程序提供物品，让用户为物品付费，“赠送”物品，并更新每个物品的库存。它似乎或多或少起到了作用。我有两个问题：

1)我不知道在用户回答'n‘到’购买其他东西？(y/n)：‘之后如何退出自动售货机程序。

2)有没有办法让代码变得更简单/更好？

def vend():

    a = {'item': 'choc', 'price': 1.5, 'stock': 2}
    b = {'item': 'pop', 'price': 1.75, 'stock': 1}
    c = {'item': 'chips', 'price': 2.0, 'stock': 3}
    d = {'item': 'gum', 'price': 0.50, 'stock': 1}
    e = {'item': 'mints', 'price': 0.75, 'stock': 3}
    items = [a, b, c, d, e]
    cim = 0 # cash in machine

    print('welcome to vending machine! \n***************')

    # show items, prices
    def show(items):
        print('\nitems available \n***************')

        for item in items:      
            if item.get('stock') == 0:
                items.remove(item)
        for item in items:
            print(item.get('item'), item.get('price'))

        print('***************\n')

    # have user choose item
    while True:
        show(items)
        selected = input('select item: ')
        for item in items:
            if selected == item.get('item'):
                selected = item               
                price = selected.get('price')
                while cim < price:
                    cim = float(input('insert ' + str(price - cim) + ': '))   
                else:
                    print('you got ' + selected.get('item'))
                    selected['stock'] -= 1
                    cim -= price
                    print('cash remaining: ' + str(cim))
                    a = input('buy something else? (y/n): ')
                    if a == 'n':
                        if cim != 0:
                            print(str(cim) + ' refunded')
                            cim = 0
                            print('thank you, have a nice day!\n')
                            break                        
                        else:
                            print('thank you, have a nice day!\n')
                            break                        
                    else:
                        continue



vend()

Answer 1

1)我不知道在用户回答'n‘到’购买其他东西？(y/n)：‘之后如何退出自动售货机程序。

Python语言中的break语句中断了包含它的第一个for或while循环。您只是退出了所示的for循环。while True条件会让您永远循环。

但是，您做了一些聪明的事情，您将所有自动售货机功能都包含在您的自动售货机函数中。如果您使用return语句代替break，您不仅会退出自动售货函数，而且会到达整个程序的末尾，并按您的意愿退出。

return 语句也用于从函数调用返回值，但在本例中不需要这样做。

此外，您不需要也不应该从函数中使用两个独立的出口。删除以下三行：

                else:
                    print('thank you, have a nice day!\n')
                    break

突出您删除的三行上的两行，并将break替换为return。

你还可以做其他的改进，但这只是一个开始。

Answer 2

您只需要添加一个布尔变量，如果用户的答案是n，则将该变量设置为false。还请注意，代码中有一个问题，您没有以正确的方式更新cim的值。你必须考虑到一个人可能需要输入多个硬币，所以你必须累计插入的硬币总数：

def vend():

    a = {'item': 'choc', 'price': 1.5, 'stock': 2}
    b = {'item': 'pop', 'price': 1.75, 'stock': 1}
    c = {'item': 'chips', 'price': 2.0, 'stock': 3}
    d = {'item': 'gum', 'price': 0.50, 'stock': 1}
    e = {'item': 'mints', 'price': 0.75, 'stock': 3}
    items = [a, b, c, d, e]
    cim = 0 # cash in machine

    print('welcome to vending machine! \n***************')

    # show items, prices
    def show(items):
        print('\nitems available \n***************')

        for item in items:      
            if item.get('stock') == 0:
                items.remove(item)
        for item in items:
            print(item.get('item'), item.get('price'))

        print('***************\n')
    continueToBuy = True
    # have user choose item
    while continueToBuy == True:
        show(items)
        selected = input('select item: ')
        for item in items:
            if selected == item.get('item'):
                selected = item               
                price = selected.get('price')
                while cim < price:
                    cim = cim + float(input('insert ' + str(price - cim) + ': '))   

                print('you got ' + selected.get('item'))
                selected['stock'] -= 1
                cim -= price
                print('cash remaining: ' + str(cim))
                a = input('buy something else? (y/n): ')
                if a == 'n':
                    continueToBuy = False

                    if cim != 0:
                        print(str(cim) + ' refunded')
                        cim = 0
                        print('thank you, have a nice day!\n')
                        break                        
                    else:
                        print('thank you, have a nice day!\n')
                        break  
                else:
                    continue



vend()

此外，我认为这是引入面向对象编程的一个很好的例子。它可以让你拥有更好的结构化代码，并让你专注于你想要开发的逻辑。下面是一个可能的实现：

class Item:
    def __init__(self, name, price, stock):
        self.name = name
        self.price = price
        self.stock = stock

    def updateStock(self, stock):
        self.stock = stock

    def buyFromStock(self):
        if self.stock == 0:
            # raise not item exception
            pass
        self.stock -= 1

class VendingMachine:
    def __init__(self):
        self.amount = 0
        self.items = []

    def addItem(self, item):
        self.items.append(item)

    def showItems(self):
        print('\nitems available \n***************')

        for item in self.items:      
            if item.stock == 0:
                self.items.remove(item)
        for item in self.items:
            print(item.name, item.price)

        print('***************\n')

    def addCash(self, money):
        self.amount = self.amount + money

    def buyItem(self, item):
        if self.amount < item.price:
            print('You can\'t but this item. Insert more coins.')
        else:
            self.amount -= item.price
            item.buyFromStock()
            print('You got ' +item.name)
            print('Cash remaining: ' + str(self.amount))

    def containsItem(self, wanted):
        ret = False
        for item in self.items:
            if item.name == wanted:
                ret = True
                break
        return ret

    def getItem(self, wanted):
        ret = None
        for item in self.items:
            if item.name == wanted:
                ret = item
                break
        return ret

    def insertAmountForItem(self, item):
        price = item.price
        while self.amount < price:
                self.amount = self.amount + float(input('insert ' + str(price - self.amount) + ': '))

    def checkRefund(self):
        if self.amount > 0:
            print(self.amount + " refunded.")
            self.amount = 0

        print('Thank you, have a nice day!\n')


def vend():

    machine = VendingMachine()
    item1 = Item('choc',  1.5,  2)
    item2 = Item('pop', 1.75,  1)
    item3 = Item('chips',  2.0,  3)
    item4 = Item('gum',  0.50, 1)
    item5 = Item('mints',0.75,  3)
    machine.addItem(item1)
    machine.addItem(item2)
    machine.addItem(item3)
    machine.addItem(item4)
    machine.addItem(item5)

    print('Welcome to the vending machine!\n***************')

    continueToBuy = True
    while continueToBuy == True:
        machine.showItems()
        selected = input('select item: ')
        if machine.containsItem(selected):
            item = machine.getItem(selected)

            machine.insertAmountForItem(item)
            machine.buyItem(item)

            a = input('buy something else? (y/n): ')
            if a == 'n':
                continueToBuy = False
                machine.checkRefund()
            else:
                continue

        else:
            print('Item not available. Select another item.')
            continue

vend()

有关OOP的更多信息，请参阅a resource like this。