Question

您好我在使用字符串名称调用函数时有疑问，因为它显示错误：列表指示必须是整数

我同意错误陈述，但不知道该怎么做。当我将函数参数参数作为字典（选项2）给出时，其功能是接受它并顺利运行代码。但是只给它一个密钥的名称（就像我在选项1中所做的那样），它显示了Indices错误，因为我正在访问key，这是一个字符串而不是整数＆amp;它没有带有值的键（这是不可用键的错误）。所以，

请解释我：

如何创建具有键名但空值的字典。如何比较它是否是列表名称在函数的参数或字典键中给出。请建议代码。解决我的代码。对于选项1

代码：

 # CODE FOR DETRMINING PRICE AS PER STOCK
#PYTHON 2.7 SCRIPT 
stock = {
    "banana": 6,
    "apple": 0,
    "orange": 32,
    "pear": 15
}

prices = {
    "banana": 4,
    "apple": 2,
    "orange": 1.5,
    "pear": 3
}

def compute_bill(food):
    x = 0
    total1 = 0
    total2 = 0
    z=0

    for key in food: # I KNOW I AM DOING ERROR HERE, BUT NO CLUE WHAT TO DO!!

        count = stock[key] #INTIAL COUNT
        print "this is the stock of %s : %d " % (key,count)

        count = stock[key] - food[key] # STOCK REMAINING
        print "this is the stock remaining of %s : %d " % (key,count)

        if count > 0: # CHECKING WHETHER IT IS IN STOCK OR NOT
            z = prices[key] * food[key] # FINDING TOTAL
            total1 = z + total1 # ACCUMLATING TOTAL
            print "this is the total1 of %s : %f \n" % (key,z)

        elif count <= 0: # OVER-STOCK OR EMPTY STOCK
            z = prices[key] * stock[key]
            total2 = z + total2
            print "this is the total2 of %s : %f \n" % (key,z)

        x = total1 + total2 #COMPUTING WHOLE TOTAL



    print "\n this is the whole total : %f \n" % x

    return x



 # JST WANT ALL PEAR
compute_bill(['pear']) #OPTION 1: NOT WORKING!! NEED SOLUTION

#OPTION 2 : WORKING : 
order = {'apple' : 1, 'banana' : 3, 'pear' : 3, 'orange' : 3}
    compute_bill(order)

提前谢谢＆amp;干杯!!

Answer 1

这意味着您传递的不是整数作为列表索引。从它的外观来看，compute_bill()在列表中使用名为'pear'的字符串进行调用。然后该列表作为参数food传递。然后for语句将'pear'字符串作为键，如果将其应用于字典stock，则该字符串是正确的。但是，food仍然是一个列表，因此调用food['pear']会出错。它应该是food[0]。你可以用这个代替循环：

    for i in range(len(food)):
        key = food[i]

之后，您可以分别使用索引i和密钥key访问列表和字典。在这种情况下，food[0]不会产生整数值，但会使用字符串'pear'。

Answer 2

您需要检查传入的对象是字典（order）还是列表（item）...您还需要在第二个确切地确定您想要的行为但是，我想您想要回答可用库存的总价格：

def compute_bill(food):
    if isinstance(food, dict):
        compute_bill_for_order(food)
    if isinstance(food, list):
        compute_bill_for_items(food)

def compute_bill_for_order(order):
    for key in order.keys():  ## You also have to call the `keys` method
      # Here goes the exact same code you have for the cases
      # count > 0 and count <= 0
      # Basically, the `compute_bill` method
      pass

def compute_bill_for_items(items):
    total = 0
    for item in items:
        total += prices[item] * stock[item]
    return total

Answer 3

作为循环食物的每次迭代的开始，在compute_bill函数中，我会提取所需食物的数量：

try:
  quantity = food[key]  # get only how much was asked
except TypeError:
  quantity = stock[key] # get all remaining food from the stock !

然后，只要您使用food[key]，请使用新变量quantity。

列表指数错误在Python 2.7中，请在代码中为OPTION 1建议解决方案

3 个答案: