Question

我需要编写一个代码，每次有人购买产品时，需求字典中的密钥就会增加1。我不知道如何通过知道值来增加字典中的键。

这是我尝试过的：

demand = {"bread":0,"butter":0,"cheese":0, "water":0,"ice cream":0}
# bread is the value and 0 is the key, which I want to increase every time

def bill(buy_lst):
    for item in buy_lst:
        demand[demand.get(item)] += 1

我运行时说：

demand[demand.get(item)] += 1
KeyError: 0

谢谢！

Answer 1

您似乎误解了key和value，在您的情况下，字符串为keys，其数量为value

demand = {"bread": 0, "butter": 0, "cheese": 0, "water": 0, "ice cream": 0}

所以，您想要的是给定键的增加值

buy_lst[item] += 1

要使用它，您需要向用户询问一种产品，例如

def bill(buy_lst):
    item = None
    while not item:
        item = input("Please select in " + str(list(buy_lst.keys())))
        item = item if item in buy_lst else None
    buy_lst[item] += 1


if __name__ == '__main__':
    demand = {"bread": 0, "butter": 0, "cheese": 0, "water": 0, "ice cream": 0}
    bill(demand)
    print(demand)

Answer 2

您的问题是您如何添加字典。请注意以下几点：

demand = {"bread": 0, "butter": 0, "cheese": 0, "water": 0, "ice cream": 0}
buy_lst = ["bread", "butter", "bread"]

def bill(buy_lst):
    for item in buy_lst:
        print(demand.get(item))
        #demand[demand.get(item)] += 1

bill(buy_lst)

这将输出：

0
0
0

因此，换句话说，就是您的：

demand[demand.get(item)] += 1

您正在做

demand[0] += 1

哪个将返回错误：

Traceback (most recent call last):
  File "/Users/felipefaria/Desktop/test/main.py", line 11, in <module>
    bill(buy_lst)
  File "/Users/felipefaria/Desktop/test/main.py", line 8, in bill
    demand[demand.get(item)] += 1
KeyError: 0

相反，您应该仅在括号内引用项目本身，如下所示：

demand = {"bread": 0, "butter": 0, "cheese": 0, "water": 0, "ice cream": 0}
buy_lst = ["bread", "butter", "bread"]

def bill(buy_lst):
    for item in buy_lst:
        demand[item] += 1

bill(buy_lst)
print(demand)

哪个会输出：

{'bread': 2, 'butter': 1, 'cheese': 0, 'water': 0, 'ice cream': 0}

Answer 3

我认为您试图表达的意思是“增加我所知道的钥匙的价值”。因为只有值是整数，所以只有它们可以递增。因此，递增值将是：

demand = {"bread":0,"butter":0,"cheese":0, "water":0,"ice cream":0}

def bill(buy_lst):
    for item in buy_lst:
        demand[item] += 1

为澄清起见，词典项目的第一部分是key，第二部分是value。

Answer 4

您可能会混淆键和值。在demand中，键是项目，值是计数。

#!/usr/bin/env python

demand = {"bread":0, "butter":0, "cheese":0, "water":0, "ice cream":0}
def bill(buy_list):
    for item in buy_list:
        demand[item] += 1

buy_list = ["bread", "water"]

print("Before billing:")
print(demand)

bill(buy_list)

print("After billing")
print(demand)

此打印：

Before billing:
{'bread': 0, 'butter': 0, 'cheese': 0, 'water': 0, 'ice cream': 0}
After billing
{'bread': 1, 'butter': 0, 'cheese': 0, 'water': 1, 'ice cream': 0}

Answer 5

您的问题确实很简单。您只需要在函数参数*前面添加运算符buy_lst，就可以拥有*buylst。请参见以下代码：

demand = {"bread":0,"butter":0,"cheese":0, "water":0,"ice cream":0}
# bread is the value and 0 is the key, which I want to increase every time

def bill(*buy_lst):  # see this line
    for item in buy_lst:
        demand[item] += 1  # see this line

bill("bread", "cheese") # The client buys the products `bread` and `cheese`
print(demand)
bill("bread", "cheese", "water", "butter")
print(demand)

输出

{'bread': 1, 'butter': 0, 'cheese': 1, 'water': 0, 'ice cream': 0}
{'bread': 2, 'butter': 1, 'cheese': 2, 'water': 1, 'ice cream': 0}

通过知道值来增加键-python字典

5 个答案: