列表/元组槽中值的总和

Question

我似乎不知道如何得到列表/元组中的值之和

我试过使用键和其他一些方法，但都不管用

#initialise variables
products = []
totalCost = 0.0


#input products and prices funtions
def getInput():
    product_name = input("What is the product?")
    product_price = input("What s the price?")

    return (product_name, product_price)

#collect input
for x in range(5):
    product = getInput()
    products.append(product)

#sort list
products.sort(key=lambda t: t[1], reverse=True)


#show list
def showTable():
    for x in range(5):
        print("Product Name | Price: ", products[x])

#calculate cheapest
def cheapestItem():
    print("The cheapest item in this list is: ", min(products, key = lambda t: t[1]))
    print("Congratulations you get this item free")

    #calculate total
    totalCost = sum(products[1]) - min(products[1])


#main
showTable()
cheapestItem()

我想得到价格的总和，然后从清单中减去最小的金额。你知道吗

Answer 1

您有几个问题：

您没有数字，只有字符串：

def getInput():
    product_name = input("What is the product?")   # string
    product_price = input("What s the price?")     # string

    return (product_name, product_price)

修正（只是价格输入部分）：

      while True:
          try: 
              product_price = int(input("What s the price?"))
              if product_price <= 0:
                  raise ValueError
              break
          except ValueError:
              print("Not a valid price")

请参阅Asking the user for input until they give a valid response以了解如何避免ValueError的其他方法

只要没有数字，'1000'就会小于'2'（按字母顺序比较）。你知道吗

您最便宜的项目计算并不能完成它应该做的事情：

即使您将产品固定为有数字，您的totalCost也不起作用：

product[1] # this is the 2nd element of your list - not the price of it


def cheapestItem():
    print("The cheapest item in this list is: ", min(products, key = lambda t: t[1]))
    print("Congratulations you get this item free")

    #calculate total
    totalCost = sum(products[1]) - min(products[1])

固定（f.e.）：

   # assumes numbers in ("icecream", 42) - not strings
   sortedItems = sorted(products, lambda x:x[1])  # sort by price ascending

   minItem   = sortedItems[0]
   totalCost = sum(item[1] for item in sortedItems[1:])   # don't calc the lowest value
   totalCost = sum(products[1]) - min(products[1])

使用min()也可以，但是通过排序，您可以使用列表切片对除最低值之外的所有值求和。如果您有庞大的列表-min()更为理想：

   minItem = min(products, lambda x:x[1])
   total = sum(item[1] for item in products) - minItem[1]  # reduced by minItems cost

---

我将代码固定为使用提供给函数的参数，而不是全局参数-也不需要min（）产品列表，因为您可以对其进行排序-您只需切掉最低的项并扣除其值：

固定代码和示例输入：

def getInput():
    product_name = input("What is the product? ")
    while True: 
        try:
            # whole number prices assumed, else use float( input ( ... ))
            product_price = int(input("What s the price? "))
            if product_price <= 0:
                raise ValueError
            break
        except ValueError:
            print("Wrong input - prices must be greater 0 and whole numbers")

    return (product_name, product_price)

def showTable(p):
    for x in p:
        print("Product Name | Price: ", x[0],x[1])

def cheapestItem(p):
    # assumes sorted list of items in p
    print("The cheapest item in this list is: ", p[-1])
    print("Congratulations you get this item free")

    #calculate total
    totalCost = sum(i[1] for i in p[:-1])
    print("Total Cost:", totalCost, "You saved:", p[-1])


products = [] 
for x in range(5):
    product = getInput()
    products.append(product)

# sort list - cheapestItem(..) needs a sorted input to work
products.sort(key=lambda t: t[1], reverse=True)

showTable(products)
cheapestItem(products)

输出：

What is the product? apple
What s the price? 22
What is the product? pear
What s the price? 11
What is the product? kiwi
What s the price? 5
What is the product? pineapple
What s the price? no idea
Wrong input - prices must be greater 0 and whole numbers
What s the price? 100
What is the product? gears
What s the price? 1

Product Name | Price:  pineapple 100
Product Name | Price:  apple 22
Product Name | Price:  pear 11
Product Name | Price:  kiwi 5
Product Name | Price:  gears 1
The cheapest item in this list is:  ('gears', 1)
Congratulations you get this item free
Total Cost: 138 You saved: ('gears', 1)