25 使用Python处理JSON数据

25.1 JSON简介

25.1.1 什么是JSON

    JSON全称为JavaScript Object Notation,一般翻译为JS标记,是一种轻量级的数据交换格式。是基于ECMAScript的一个子集,采用完全独立于编程语言的文本格式来存储和表示数据。简洁和清晰的层次结构使得JSON成为理想的数据交换语言,其主要特点有:易于阅读易于机器生成有效提升网络速度等。

25.1.2 JSON的两种结构

    JSON简单来说,可以理解为JavaScript中的数组对象,通过这两种结构,可以表示各种复杂的结构。

25.1.2.1 数组

    数组在JavaScript是使用中括号[ ]来定义的,一般定义格式如下所示:

let array=["Surpass","28","Shanghai"];

    若要对数组取值,则需要使用索引。元素的类型可以是数字字符串数组对象等。

25.1.2.2 对象

    对象在JavaScript是使用大括号{ }来定义的,一般定义格式如下所示:

let personInfo={
  name:"Surpass",
  age:28,
  location:"Shanghai"
}

    对象一般是基于keyvalue,在JavaScript中,其取值方式也非常简单variable.key即可。元素value的类型可以是数字字符串数组对象等。

25.1.3 支持的数据格式

    JSON支持的主要数据格式如下所示:

  • 数组:使用中括号
  • 对象:使用大括号
  • 整型浮点型布尔类型null
  • 字符串类型:必须使用双引号,不能使用单引号

    多个数据之间使用逗号做为分隔符,基与Python中的数据类型对应表如下所示:

JSON Python
Object dict
array list
string str
number(int) int
number(real) float
true True
false False
null None

25.2 Python对JSON的支持

25.2.1 Python 和 JSON 数据类型

    在Python中主要使用json模块来对JSON数据进行处理。在使用前,需要导入json模块,用法如下所示:

import json

    json模块中主要包含以下四个操作函数,如下所示:

    在json的处理过种中,Python中的原始类型与JSON类型会存在相互转换,具体的转换表如下所示:

  • Python 转换为 JSON
Python JSON
dict Object
list array
tuple array
str string
int number
float number
True true
False false
None null
  • JSON 转换为 Python
JSON Python
Object dict
array list
string str
number(int) int
number(real) float
true True
false False
null None

25.2.2 json模块常用方法

    关于Python 内置的json模块,可以查看之前我写的文章:https://www.cnblogs.com/surpassme/p/13034972.html

25.3 使用JSONPath处理JSON数据

    内置的json模块,在处理简单的JSON数据时,易用且非常非常方便,但在处理比较复杂且特别大的JSON数据,还是有一些费力,今天我们使用一个第三方的工具来处理JSON数据,叫JSONPath

25.3.1 什么是JSONPath

    JSONPath是一种用于解析JSON数据的表达语言。经常用于解析和处理多层嵌套的JSON数据,其用法与解析XML数据的XPath表达式语言非常相似。

25.3.2 安装

    安装方法如下所示:

# pip install -U jsonpath

25.3.3 JSONPath语法

    JSONPath语法与XPath非常相似,其对应参照表如下所示:

XPath JSONPath 描述
/ $ 根节点/元素
. @ 当前节点/元素
/ . or [] 子元素
.. n/a 父元素
// .. 递归向下搜索子元素
* * 通配符,表示所有元素
@ n/a 访问属性,JSON结构的数据没有这种属性
[] [] 子元素操作符(可以在里面做简单的迭代操作,如数据索引,根据内容选值等)
| [,] 支持迭代器中做多选
n/a [start :end :step] 数组分割操作
[] ?() 筛选表达式
n/a () 支持表达式计算
() n/a 分组,JSONPath不支持

以上内容可查阅官方文档:https://goessner.net/articles/JsonPath/

    我们以下示例数据为例,来进行对比,如下所示:

{ "store": 
  {
    "book": [ 
      { "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      { "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
      },
      { "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      },
      { "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}
XPath JSONPath 结果
/store/book/author $.store.book[*].author 获取book节点中所有author
//author $..author 获取所有author
/store/* $.store.* 获取store的元素,包含book和bicycle
/store//price $.store..price 获取store中的所有price
//book[3] $..book[2] 获取第三本书所有信息
//book[last()] $..book[(@.length-1)]
$..book[-1:]
获取最后一本书的信息
//book[position()️] $..book[0,1]
$..book[:2]
获取前面的两本书
//book[isbn] $..book[?(@.isbn)] 根据isbn进行过滤
//book[price<10] $..book[?(@.price<10)] 根据price进行筛选
//* $..* 所有元素

在XPath中,下标是1开始,而在JSONPath中是从0开始

JSONPath在线练习网址:http://jsonpath.com/

25.3.4 JSONPath用法

    其基本用法形式如下所示:

jsonPath(obj, expr [, args])

    基参数如下所示:

  • obj (object|array):

    JSON数据对象

  • expr (string):

    JSONPath表达式

  • args (object|undefined):

    改变输出格式,比如是输出是值还是路径,

args.resultType可选的输出格式为:”VALUE”、”PATH”、”IPATH”

  • 返回类型为(array|false):

    若返回array,则代表成功匹配到数据,false则代表未匹配到数据。

25.3.5 在Python中的使用

from jsonpath import  jsonpath
import json

data = {
    "store":
        {
            "book": [
                {
                    "category": "reference",
                    "author": "Nigel Rees",
                    "title": "Sayings of the Century",
                    "price": 8.95
                },
                {
                    "category": "fiction",
                    "author": "Evelyn Waugh",
                    "title": "Sword of Honour",
                    "price": 12.99
                },
                {
                    "category": "fiction",
                    "author": "Herman Melville",
                    "title": "Moby Dick",
                    "isbn": "0-553-21311-3",
                    "price": 8.99
                },
                {
                    "category": "fiction",
                    "author": "J. R. R. Tolkien",
                    "title": "The Lord of the Rings",
                    "isbn": "0-395-19395-8",
                    "price": 22.99
                }
            ],
            "bicycle": {
                "color": "red",
                "price": 19.95
            }
        }
}

#  获取book节点中所有author
getAllBookAuthor=jsonpath(data,"$.store.book[*].author")
print(f"getAllBookAuthor is :{json.dumps(getAllBookAuthor,indent=4)}")
#  获取book节点中所有author
getAllAuthor=jsonpath(data,"$..author")
print(f"getAllAuthor is {json.dumps(getAllAuthor,indent=4)}")
#  获取store的元素,包含book和bicycle
getAllStoreElement=jsonpath(data,"$.store.*")
print(f"getAllStoreElement is {json.dumps(getAllStoreElement,indent=4)}")
# 获取store中的所有price
getAllStorePriceA=jsonpath(data,"$[store]..price")
getAllStorePriceB=jsonpath(data,"$.store..price")
print(f"getAllStorePrictA is {getAllStorePriceA}\ngetAllStorePriceB is {getAllStorePriceB}")
# 获取第三本书所有信息
getThirdBookInfo=jsonpath(data,"$..book[2]")
print(f"getThirdBookInfo is {json.dumps(getThirdBookInfo,indent=4)}")
# 获取最后一本书的信息
getLastBookInfo=jsonpath(data,"$..book[-1:]")
print(f"getLastBookInfo is {json.dumps(getLastBookInfo,indent=4)}")
# 获取前面的两本书
getFirstAndSecondBookInfo=jsonpath(data,"$..book[:2]")
print(f"getFirstAndSecondBookInfo is {json.dumps(getFirstAndSecondBookInfo,indent=4)}")
#  根据isbn进行过滤
getWithFilterISBN=jsonpath(data,"$..book[?(@.isbn)]")
print(f"getWithFilterISBN is {json.dumps(getWithFilterISBN,indent=4)}")
# 根据price进行筛选
getWithFilterPrice=jsonpath(data,"$..book[?(@.price<10)]")
print(f"getWithFilterPrice is {json.dumps(getWithFilterPrice,indent=4)}")
# 所有元素
getAllElement=jsonpath(data,"$..*")
print(f"getAllElement is {json.dumps(getAllElement,indent=4)}")
# 未能匹配到元素时
noMatchElement=jsonpath(data,"$..surpass")
print(f"noMatchElement is {noMatchElement}")
# 调整输出格式
controlleOutput=jsonpath(data,expr="$..author",result_type="PATH")
print(f"controlleOutput is {json.dumps(controlleOutput,indent=4)}")

    最终输出结果如下扬尘:

getAllBookAuthor is :[
    "Nigel Rees",
    "Evelyn Waugh",
    "Herman Melville",
    "J. R. R. Tolkien"
]
getAllAuthor is [
    "Nigel Rees",
    "Evelyn Waugh",
    "Herman Melville",
    "J. R. R. Tolkien"
]
getAllStoreElement is [
    [
        {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
        },
        {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
        },
        {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
        },
        {
            "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
        }
    ],
    {
        "color": "red",
        "price": 19.95
    }
]
getAllStorePrictA is [8.95, 12.99, 8.99, 22.99, 19.95]
getAllStorePriceB is [8.95, 12.99, 8.99, 22.99, 19.95]
getThirdBookInfo is [
    {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
    }
]
getLastBookInfo is [
    {
        "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
    }
]
getFirstAndSecondBookInfo is [
    {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
    },
    {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
    }
]
getWithFilterISBN is [
    {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
    },
    {
        "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
    }
]
getWithFilterPrice is [
    {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
    },
    {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
    }
]
getAllElement is [
    {
        "book": [
            {
                "category": "reference",
                "author": "Nigel Rees",
                "title": "Sayings of the Century",
                "price": 8.95
            },
            {
                "category": "fiction",
                "author": "Evelyn Waugh",
                "title": "Sword of Honour",
                "price": 12.99
            },
            {
                "category": "fiction",
                "author": "Herman Melville",
                "title": "Moby Dick",
                "isbn": "0-553-21311-3",
                "price": 8.99
            },
            {
                "category": "fiction",
                "author": "J. R. R. Tolkien",
                "title": "The Lord of the Rings",
                "isbn": "0-395-19395-8",
                "price": 22.99
            }
        ],
        "bicycle": {
            "color": "red",
            "price": 19.95
        }
    },
    [
        {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
        },
        {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
        },
        {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
        },
        {
            "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
        }
    ],
    {
        "color": "red",
        "price": 19.95
    },
    {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
    },
    {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
    },
    {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
    },
    {
        "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
    },
    "reference",
    "Nigel Rees",
    "Sayings of the Century",
    8.95,
    "fiction",
    "Evelyn Waugh",
    "Sword of Honour",
    12.99,
    "fiction",
    "Herman Melville",
    "Moby Dick",
    "0-553-21311-3",
    8.99,
    "fiction",
    "J. R. R. Tolkien",
    "The Lord of the Rings",
    "0-395-19395-8",
    22.99,
    "red",
    19.95
]
noMatchElement is False
controlleOutput is [
    "$['store']['book'][0]['author']",
    "$['store']['book'][1]['author']",
    "$['store']['book'][2]['author']",
    "$['store']['book'][3]['author']"
]

原文地址:https://www.jianshu.com/p/a69a9cf293bd

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