Python 字典只保留最后一次循环迭代的信息

Question

我正在尝试创建一个循环来填充来自 Series 的字典中的字典：
预期结果是：

{1: {'KEY Mult. by 10': 10, 'KEY Add by 10': 11}, 2: {'KEY Mult. by 10': 20, 'KEY Add by 10': 12}, 3: {'KEY Mult. by 10': 30, 'KEY Add by 10': 13}, 4: {'KEY Mult. by 10': 40, 'KEY Add by 10': 14}, 5: {'KEY Mult. by 10': 50, 'KEY Add by 10': 15}}

我正在做的是：

series_1 = pd.Series([1,2,3,4,5]) first_dict = dict() # creating first level of Dict second_dict = dict({'KEY Mult. by 10': 0, # creating second level of Dict 'KEY Add by 10': 0}) for i in series_1: first_dict[i] = second_dict first_dict[i]['KEY Mult. by 10'] = i *10 first_dict[i]['KEY Add by 10'] = i + 10

以上结果为：

{1: {'KEY Mult. by 10': 50, 'KEY Add by 10': 15}, 2: {'KEY Mult. by 10': 50, 'KEY Add by 10': 15}, 3: {'KEY Mult. by 10': 50, 'KEY Add by 10': 15}, 4: {'KEY Mult. by 10': 50, 'KEY Add by 10': 15}, 5: {'KEY Mult. by 10': 50, 'KEY Add by 10': 15}}

然后，当我尝试更改其中一个键的值时，它会更改所有键：

first_dict[3]['KEY Mult. by 10'] = 20 print(first_dict) {1: {'KEY Mult. by 10': 20, 'KEY Add by 10': 15}, 2: {'KEY Mult. by 10': 20, 'KEY Add by 10': 15}, 3: {'KEY Mult. by 10': 20, 'KEY Add by 10': 15}, 4: {'KEY Mult. by 10': 20, 'KEY Add by 10': 15}, 5: {'KEY Mult. by 10': 20, 'KEY Add by 10': 15}}

谁能帮帮我吗？

Answer 1

将 first_dict[i] = second_dict 更改为：first_dict[i] = dict() 它将按预期工作，这样做您还可以删除“第二级 Dict”的创建

Answer 2

问题是，你多次使用同一个词典，你必须使用一个副本哦 second_dict

import pandas as pd

series_1 = pd.Series([1, 2, 3, 4, 5])

first_dict = dict()  # creating first level of Dict
second_dict = dict({'KEY Mult. by 10': 0,  # creating second level of Dict
                    'KEY Add by 10': 0})

for i in series_1:
    first_dict[i] = second_dict.copy()

    first_dict[i]['KEY Mult. by 10'] = i * 10
    first_dict[i]['KEY Add by 10'] = i + 10

Answer 3

一些评论描述了解决方案，但我会详细说明一些。

字典是每个外部索引中的同一块内存。在你运行:

之后看到这个

for i in series_1:
    first_dict[i] = second_dict

查看两个内部词典的id()，这些是内存位置：

id(first_dict[1]) # 4511987904
id(first_dict[2])

按照当前编写代码的方式，对任何字典的任何写入都会覆盖所有字典。
在您的机器上，您将有一个（一个）不同的 id 值，但它是相同的 idea-they 将都是相同的内存位置。

要解决此问题，您可以调用构造函数 inside for 循环，它将分配新内存 对于每个内部字典。

for i in series_1:
    first_dict[i] = dict({'KEY Mult. by 10': 0,'KEY Add by 10': 0})
    first_dict[i]['KEY Mult. by 10'] = i * 10
    first_dict[i]['KEY Add by 10'] = i + 10

然后您将看到每个内部字典的不同 id() return 值，您可以使用 id():

确认它们是不同的内存位置

>>> id(first_dict[3])
4511988352
>>> id(first_dict[1])
4511988160

同样，在您的机器上这些值将是不同的 id()，但想法是相同的，您正在分别为每个内部字典制作 space。

Python 字典只保留最后一次循环迭代的信息

Python dictionary only keeps information from last iteration of loop

python

dictionary

loops