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[#]: collector: (lujun9972)
[#]: translator: (HankChow)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Save and load Python data with JSON)
[#]: via: (https://opensource.com/article/19/7/save-and-load-data-python-json)
[#]: author: (Seth Kenlon https://opensource.com/users/seth)
Save and load Python data with JSON
======
The JSON format saves you from creating your own data formats, and is
particularly easy to learn if you already know Python. Here's how to use
it with Python.
![Cloud and databsae incons][1]
[JSON][2] stands for JavaScript Object Notation. This format is a popular method of storing data in key-value arrangements so it can be parsed easily later. Don’t let the name fool you, though: You can use JSON in Python—not just JavaScript—as an easy way to store data, and this article demonstrates how to get started.
First, take a look at this simple JSON snippet:
```
{
        "name":"tux",
        "health":"23",
        "level":"4"
}
```
That's pure JSON and has not been altered for Python or any other language. Yet if you’re familiar with Python, you might notice that this example JSON code looks an awful lot like a Python dictionary. In fact, the two are very similar: If you are comfortable with Python lists and dictionaries, then JSON is a natural fit for you.
### Storing data in JSON format
You might consider using JSON if your application needs to store somewhat complex data. While you may have previously resorted to custom text configuration files or data formats, JSON offers you structured, recursive storage, and Python’s JSON module offers all of the parsing libraries necessary for getting this data in and out of your application. So, you don’t have to write parsing code yourself, and other programmers don’t have to decode a new data format when interacting with your application. For this reason, JSON is easy to use, and ubiquitous.
Here is some sample Python code using a dictionary within a dictionary:
```
#!/usr/bin/env python3
import json
# instantiate an empty dict
team = {}
# add a team member
team['tux'] = {'health': 23, 'level': 4}
team['beastie'] = {'health': 13, 'level': 6}
team['konqi'] = {'health': 18, 'level': 7}
```
This code creates a Python dictionary called **team**. It’s empty initially (you can create one that's already populated, but that’s impossible if you don’t have the data to put into the dictionary yet).
To add to the **dict** object, you create a key, such as **tux**, **beastie**, or **konqi** in the example code, and then provide a value. In this case, the value is _another_ dictionary full of player statistics.
Dictionaries are mutable. You can add, remove, and update the data they contain as often as you please. This format is ideal storage for data that your application frequently uses.
### Saving data in JSON format 
If the data you’re storing in your dictionary is user data that needs to persist after the application quits, then you must write the data to a file on disk. This is where the JSON Python module comes in:
```
with open('mydata.json', 'w') as f:
    json.dump(team, f)
```
This code block creates a file called **mydata.json** and opens it in write mode. The file is represented with the variable **f** (a completely arbitrary designation; you can use whatever variable name you like, such as **file**, **FILE**, **output**, or practically anything). Meanwhile, the JSON module’s **dump** function is used to dump the data from the **dict** into the data file.
Saving data from your application is as simple as that, and the best part about this is that the data is structured and predictable. To see, take a look at the resulting file:
```
$ cat mydata.json
{"tux": {"health": 23, "level": 4}, "beastie": {"health": 13, "level": 6}, "konqi": {"health": 18, "level": 7}}
```
### Reading data from a JSON file
If you are saving data to JSON format, you probably want to read the data back into Python eventually. To do this, use the Python JSON module’s **json.load** function:
```
#!/usr/bin/env python3
import json
f = open('mydata.json')
team = json.load(f)
print(team['tux'])
print(team['tux']['health'])
print(team['tux']['level'])
print(team['beastie'])
print(team['beastie']['health'])
print(team['beastie']['level'])
# when finished, close the file
f.close()
```
This function implements the inverse, more or less, of saving the file: an arbitrary variable (**f**) represents the data file, and then the JSON module’s **load** function dumps the data from the file into the arbitrary **team** variable.
The **print** statements in the code sample demonstrate how to use the data. It can be confusing to compound **dict** key upon **dict** key, but as long as you are familiar with your own dataset, or else can read the JSON source to get a mental map of it, the logic makes sense.
Of course, the **print** statements don’t have to be hard-coded. You could rewrite the sample application using a **for** loop:
```
for i in team.values():
    print(i)
```
### Using JSON
As you can see, JSON integrates surprisingly well with Python, so it’s a great format when your data fits in with its model. JSON is flexible and simple to use, and learning one basically means you’re learning the other, so consider it for data storage the next time you’re working on a Python application.
--------------------------------------------------------------------------------
via: https://opensource.com/article/19/7/save-and-load-data-python-json
作者：[Seth Kenlon][a]
选题：[lujun9972][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://opensource.com/users/seth
[b]: https://github.com/lujun9972
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/bus_cloud_database.png?itok=lhhU42fg (Cloud and databsae incons)
[2]: https://json.org

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[#]: collector: (lujun9972)
[#]: translator: (HankChow)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Save and load Python data with JSON)
[#]: via: (https://opensource.com/article/19/7/save-and-load-data-python-json)
[#]: author: (Seth Kenlon https://opensource.com/users/seth)
使用 Python 处理 JSON 格式数据
======
如果你不希望从头开始创造一种数据格式来存放数据，JSON 是一个很好的选择。如果你对 Python 有所了解，就更加事半功倍了。下面就来介绍一下如何使用 Python 处理 JSON 数据。
![Cloud and databsae incons][1]
[JSON][2] 的全称是 JavaScript <ruby>对象表示法<rt>Object Notation</rt></ruby>。这是一种以键值对的形式存储数据的格式，并且很容易解析，因而成为了一种被广泛使用的数据格式。另外，不要因为 JSON 名称而望文生义，JSON 并不仅仅在 JavaScript 中使用，它也可以在其它语言中使用。下文会介绍它是如何在 Python 中使用的。
首先我们给出一个 JSON 示例：
```
{
"name":"tux",
"health":"23",
"level":"4"
}
```
上面是一个和编程语言无关的原生 JSON 数据。熟悉 Python 的人会看出来这个 JSON 数据跟 Python 中的<ruby>字典<rt>dictionary</rt></ruby>长得很像。而这两者之间确实非常相似，如果你对 Python 中的列表和字典数据结构有一定的理解，那么 JSON 理解起来也不难。
### 使用字典存放数据
如果你的应用需要存储一些结构复杂的数据，不妨考虑使用 JSON 格式。对比你可能曾经用过的自定义格式的文本配置文件，JSON 提供了更加结构化的可递归的存储格式。同时，Python 自带的 `json` 模块已经提供了可以将 JSON 数据导入/导出应用时所需的所有解析库。因此，你不需要针对 JSON 自行编写代码用于解析，而其他开发人员在与你的应用进行数据交互的时候也不需要去解析新的数据格式。正是这个原因，JSON 在数据交换时被广泛地采用了。
以下是一段在 Python 中使用嵌套字典的代码：
```
#!/usr/bin/env python3
import json
# instantiate an empty dict
team = {}
# add a team member
team['tux'] = {'health': 23, 'level': 4}
team['beastie'] = {'health': 13, 'level': 6}
team['konqi'] = {'health': 18, 'level': 7}
```
这段代码声明了一个名为 `team` 的字典，并初始化为一个空字典。
如果要给这个字典添加内容，首先需要创建一个键，例如上面示例中的 `tux`、`beastie`、`konqi`，然后为这些键一一提供对应的值。上面示例中的值由一个个包含游戏玩家信息的字典充当。
字典是一种可变的变量。字典中的数据可以随时添加、删除或更新。这样的特性使得字典成为了应用程序存储数据的极好选择。
### 使用 JSON 格式存储数据
如果存放在字典中的数据需要被持久性存储，这些数据就需要写到文件当中。这个时候就需要用到 Python 中的 `json` 模块了：
```
with open('mydata.json', 'w') as f:
json.dump(team, f)
```
上面的代码首先创建了一个名为 `mydata.json` 的文件，然后以写模式打开了这个文件，这个被打开的文件以变量 `f` 表示（当然也可以用任何你喜欢的名称，例如 `file`、`output` 等）。而 `json` 模块中的 `dump()` 方法则是用于将一个字典输出到一个文件中。
从应用中导出数据就是这么简单，同时这些导出的数据是结构化的、可理解的。现在可以查看导出的数据：
```
$ cat mydata.json
{"tux": {"health": 23, "level": 4}, "beastie": {"health": 13, "level": 6}, "konqi": {"health": 18, "level": 7}}
```
### 从 JSON 文件中读取数据
如果已经将数据以 JSON 格式导出到文件中了，也有可能需要将这些数据读回到应用中去。这个时候，可以使用 Python `json` 模块中的 `load()` 方法：
```
#!/usr/bin/env python3
import json
f = open('mydata.json')
team = json.load(f)
print(team['tux'])
print(team['tux']['health'])
print(team['tux']['level'])
print(team['beastie'])
print(team['beastie']['health'])
print(team['beastie']['level'])
# when finished, close the file
f.close()
```
这个方法实现了和保存文件大致相反的操作。使用一个变量 `f` 来表示打开了的文件，然后使用 `json` 模块中的 `load()` 方法读取文件中的数据并存放到 `team` 变量中。
其中的 `print()` 展示了如何查看读取到的数据。在过于复杂的字典中迭代调用字典键的时候有可能会稍微转不过弯来，但只要熟悉整个数据的结构，就可以慢慢摸索出其中的逻辑。makes sense.
当然，这里使用 `print()` 的方式太不灵活了。你可以将其改写成使用 for 循环的形式：
```
for i in team.values():
print(i)
```
### 使用 JSON
如上所述，在 Python 中可以很轻松地处理 JSON 数据。因此只要你的数据符合 JSON 的模式，就可以选择使用 JSON。JSON 非常灵活易用，下次使用 Python 的时候不妨尝试一下。
--------------------------------------------------------------------------------
via: https://opensource.com/article/19/7/save-and-load-data-python-json
作者：[Seth Kenlon][a]
选题：[lujun9972][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://opensource.com/users/seth
[b]: https://github.com/lujun9972
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/bus_cloud_database.png?itok=lhhU42fg (Cloud and databsae incons)
[2]: https://json.org