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python - 如何从python中没有键的字典中读取？

问题描述

这是我之前的问题的后续，我正在处理多个字典并遇到问题。我目前有一个存储数据的主字典和一个添加数据的空白字典。

Dairy_goods = {1:{'item':'Milk','p':2.47,'g':0.16,'offer':'Yes'},
    2:{'item':'Butter','p':4.50,'g':0.32,'offer':'No'},
    3:{'item':'Egg','p':3.40,'g':0.24,'offer':'No'}}

shopping_basket={}

例如，我想将“牛奶”项目添加到空白购物篮中，我会按照以下方式进行。

choose=int(input('1.Item= Milk, Price= $2.47, GST= $0.16, Offer=Yes\n'
                 '2.item= Butter, Price= $4.50, GST= $0.32, Offer=No\n'
                 '3.Item= Egg, Price= $4.50, GST= $0.32, Ofer=No\n'
                 'Enter your option: '))
qnty=int(input('How many do you want?: '))
shopping_basket[Dairy_goods[choose]['item']] = shopping_basket.get(Dairy_goods[choose]['item'], 0) + qnty,Dairy_goods[choose]['p'],Dairy_goods[choose]['g'],Dairy_goods[choose]['offer']

我会得到如下输出。

print(shopping_basket)
{'Milk': (2, 2.47, 0.16, 'Yes')}

现在我想编辑这个新字典中的值，我该怎么做呢？因为它没有修复密钥？我知道它在一个元组中并且可以转换为一个列表，但仍然会给出一个错误，如下所示。

        for item in shopping_basket:
        item = str(input('key in an item to edit: '))
        for item in shopping_basket:
            shopping=list(shopping_basket) 
            qnty = int(input('Key in the quantity of %s you want: ' % item))
            shopping[item][0] = qnty # i would get a error here.
        print(shopping)

让我知道是否需要更多说明，提前谢谢你。

标签： python

解决方案

There are a few things off in your code in terms of data structures. First, a dictionary with incrementing keys {1: ..., 2: ..., ...} is basically the same as a list, so you can just as well use the simpler data structure and select items by indexing. The only thing to note here is that list indices start at 0, so you need to subtract 1 from your user's choice.

Dairy_goods = [{'item':'Milk','p':2.47,'g':0.16,'offer':'Yes'},
               {'item':'Butter','p':4.50,'g':0.32,'offer':'No'},
               {'item':'Egg','p':3.40,'g':0.24,'offer':'No'}]


choose = int(input('1.Item = ... ')) - 1 # subtract 1 to get 0-indexing
qnty = int(input('How many do you want?: '))

Next up, there is a lot going on in the line shopping_basket[Dairy_goods[choose]['item']] = ..., which makes it hard to work with. In my comment, I suggested to go for dictionaries to store the items in the shopping basket to make them easier to modify. The new format of the basket would look like

# shopping_basket
{'Milk':{'item':'Milk','p':2.47,'g':0.16,'offer':'Yes', 'qnty':1}}

which is a bit redundant because of the double item name (as key and within values), which is normally considered a bad thing, but in this case it allows for a much easier access to the shopping cart items.

However, it's actually sufficient to store only the quantities in the shopping basket - {'Milk':1, 'Egg':2, ...} - because all the other information is in Dairy_goods.

selection = Dairy_goods[choose] # e.g., {'item':'Milk','p':2.47,'g':0.16,'offer':'Yes'}
item = selection['item'] # e.g., 'Milk'

shopping_basket[item] = shopping_basket.get(item, 0) + qnty

# optional: delete item if the quantity is <= 0
if shopping_basket[item]['qnty'] <= 0:
    shopping_basket.pop(item)

Then, the edit part becomes:

item = input('key in an item to edit: ') # e.g., 'Milk'
qnty = int(input(f'Key in the quantity of {item} you want: ')) # did you hear about f-strings? Super useful!
shopping_basket[item] = qnty # set the new quantity

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