Python JSON

水深无声 2022-09-27 04:56 487阅读 0赞

# **1 JSON** #

**JSON** (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. It is based on a subset of the [JavaScript Programming Language][], [Standard ECMA-262 3rd Edition - December 1999][]. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C\#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.

JSON is built on two structures:

*  A collection of name/value pairs. In various languages, this is realized as an*object*, record, struct, dictionary, hash table, keyed list, or associative array.
 *  An ordered list of values. In most languages, this is realized as an *array*, vector, list, or sequence.

These are universal data structures. Virtually all modern programming languages support them in one form or another. It makes sense that a data format that is interchangeable with programming languages also be based on these structures.

In JSON, they take on these forms:

An *object* is an unordered set of name/value pairs. An object begins with \{  (left brace)and ends with \} (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).

![object.gif][]

An *array* is an ordered collection of values. An array begins with \[ (left bracket) and ends with \] (right bracket). Values are separated by , (comma).

![array.gif][]

A *value* can be a *string* in double quotes, or a *number*, or true or false or null, or an*object* or an *array*. These structures can be nested.

![value.gif][]

A *string* is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A character is represented as a single character string. A string is very much like a C or Java string.

![string.gif][]

A *number* is very much like a C or Java number, except that the octal and hexadecimal formats are not used.

![number.gif][]

Whitespace can be inserted between any pair of tokens. Excepting a few encoding details, that completely describes the language.

参考：http://json.org/

##  ##

## JSON 语法规则 ##

JSON 语法是 JavaScript 对象表示法语法的子集。

*  数据在名称/值对中
 *  数据由逗号分隔
 *  花括号保存对象
 *  方括号保存数组

## JSON 名称/值对 ##

JSON 数据的书写格式是：名称/值对。

名称/值对包括字段名称（在双引号中），后面写一个冒号，然后是值：

"firstName" : "John"

这很容易理解，等价于这条 JavaScript 语句：

firstName = "John"

## JSON 值 ##

JSON 值可以是：

*  数字（整数或浮点数）
 *  字符串（在双引号中）
 *  逻辑值（true 或 false）
 *  数组（在方括号中）
 *  对象（在花括号中）
 *  null

## JSON 对象 ##

JSON 对象在花括号中书写：

对象可以包含多个名称/值对：

{ "firstName":"John" , "lastName":"Doe" }

这一点也容易理解，与这条 JavaScript 语句等价：

firstName = "John"
    lastName = "Doe"

## JSON 数组 ##

JSON 数组在方括号中书写：

数组可包含多个对象：

{
    "employees": [
    { "firstName":"John" , "lastName":"Doe" },
    { "firstName":"Anna" , "lastName":"Smith" },
    { "firstName":"Peter" , "lastName":"Jones" }
    ]
    }

在上面的例子中，对象 "employees" 是包含三个对象的数组。每个对象代表一条关于某人（有姓和名）的记录。

## JSON 文件 ##

*  JSON 文件的文件类型是 ".json"
 *  JSON 文本的 MIME 类型是 "application/json"

参考：http://www.runoob.com/json/json-tutorial.html

# 2 Python JSON #

两个主要的函数是 json.dumps() 和 json.loads()

# 3 实例 #

3.1 json.dumps

在做HTTP API开发时，通过REST Client下发POST请求，请求的Payload为：

{
        "target_ip": "192.168.16.120",
        "kwargs": {
            "server_ip": "192.168.111.117"
        }
    }

HTTP请求的自定义Header是：

Accept	application/json	  
    Content-Type	application/json

当程序收到Payload后，打印结果与入库后的结果都是Unicode串：

{'target_ip': u'192.168.16.120', 'kwargs': {u'server_ip': u'192.168.111.111'}}

但是要在库中存非Unicode串，怎么做？

用json.dumps来转换字符串，转换后输出：

{"target_ip": "192.168.16.120", "kwargs": {"server_ip": "192.168.111.111"}

用python执行：

>>> import json
    >>> data = [ { 'a' : 1, 'b' : 2, 'c' : 3, 'd' : 4, 'e' : 5 } ]
    >>> json.dumps(data)
    '[{"a": 1, "c": 3, "b": 2, "e": 5, "d": 4}]'
    >>> data = {'target_ip': u'192.168.16.120', 'kwargs': {u'server_ip': u'192.168.111.111'}}
    >>> json.dumps(data)
    '{"target_ip": "192.168.16.120", "kwargs": {"server_ip": "192.168.111.111"}}'
    >>>

[JavaScript Programming Language]: http://javascript.crockford.com/
[Standard ECMA-262 3rd Edition - December 1999]: http://www.ecma-international.org/publications/files/ecma-st/ECMA-262.pdf
[object.gif]: http://json.org/object.gif
[array.gif]: /images/20220708/601be4d9f0514ef2a5f9f8243c2b27be.png
[value.gif]: http://json.org/value.gif
[string.gif]: http://json.org/string.gif
[number.gif]: http://json.org/number.gif