Python基礎-25 JSONPath用法

25 使用Python處理JSON數據

25.1 JSON簡介

25.1.1 什麼是JSON

JSON全稱爲JavaScript Object Notation，一般翻譯爲JS標記，是一種輕量級的數據交換格式。是基於ECMAScript的一個子集，採用完全獨立於編程語言的文本格式來存儲和表示數據。簡潔和清晰的層次結構使得JSON成爲理想的數據交換語言，其主要特點有：易於閱讀、易於機器生成、有效提升網絡速度等。

25.1.2 JSON的兩種結構

JSON簡單來說，可以理解爲JavaScript中的數組和對象，通過這兩種結構，可以表示各種複雜的結構。

25.1.2.1 數組

數組在JavaScript是使用中括號[ ]來定義的，一般定義格式如下所示：

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

若要對數組取值，則需要使用索引。元素的類型可以是數字、字符串、數組和對象等。

25.1.2.2 對象

對象在JavaScript是使用大括號{ }來定義的，一般定義格式如下所示：

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

對象一般是基於key和value，在JavaScript中，其取值方式也非常簡單variable.key即可。元素value的類型可以是數字、字符串、數組和對象等。

25.1.3 支持的數據格式

JSON支持的主要數據格式如下所示：

數組：使用中括號
對象：使用大括號
整型、浮點型、布爾類型和null
字符串類型：必須使用雙引號，不能使用單引號

多個數據之間使用逗號做爲分隔符，基與Python中的數據類型對應表如下所示：

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

25.2 Python對JSON的支持

25.2.1 Python 和 JSON 數據類型

在Python中主要使用json模塊來對JSON數據進行處理。在使用前，需要導入json模塊，用法如下所示：

import json

json模塊中主要包含以下四個操作函數，如下所示：

在json的處理過種中，Python中的原始類型與JSON類型會存在相互轉換，具體的轉換表如下所示：

Python 轉換爲 JSON

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

JSON 轉換爲 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模塊常用方法

關於Python 內置的json模塊，可以查看之前我寫的文章：https://www.cnblogs.com/surpassme/p/13034972.html

25.3 使用JSONPath處理JSON數據

內置的json模塊，在處理簡單的JSON數據時，易用且非常非常方便，但在處理比較複雜且特別大的JSON數據，還是有一些費力，今天我們使用一個第三方的工具來處理JSON數據，叫JSONPath。

25.3.1 什麼是JSONPath

JSONPath是一種用於解析JSON數據的表達語言。經常用於解析和處理多層嵌套的JSON數據，其用法與解析XML數據的XPath表達式語言非常相似。

25.3.2 安裝

安裝方法如下所示：

# pip install -U jsonpath

25.3.3 JSONPath語法

JSONPath語法與XPath非常相似，其對應參照表如下所示：

XPath	JSONPath	描述
/	$	根節點/元素
.	@	當前節點/元素
/	. or []	子元素
..	n/a	父元素
//	..	遞歸向下搜索子元素
*	*	通配符，表示所有元素
@	n/a	訪問屬性，JSON結構的數據沒有這種屬性
[]	[]	子元素操作符(可以在裏面做簡單的迭代操作，如數據索引，根據內容選值等)
\|	[,]	支持迭代器中做多選
n/a	[start :end :step]	數組分割操作
[]	?()	篩選表達式
n/a	()	支持表達式計算
()	n/a	分組，JSONPath不支持

以上內容可查閱官方文檔：https://goessner.net/articles/JsonPath/

我們以下示例數據爲例，來進行對比，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	結果
/store/book/author	$.store.book[*].author	獲取book節點中所有author
//author	$..author	獲取所有author
/store/*	$.store.*	獲取store的元素，包含book和bicycle
/store//price	$.store..price	獲取store中的所有price
//book[3]	$..book[2]	獲取第三本書所有信息
//book[last()]	$..book[(@.length-1)] $..book[-1:]	獲取最後一本書的信息
//book[position()❤️]	$..book[0,1] $..book[:2]	獲取前面的兩本書
//book[isbn]	$..book[?(@.isbn)]	根據isbn進行過濾
//book[price<10]	$..book[?(@.price<10)]	根據price進行篩選
//*	$..*	所有元素

在XPath中，下標是1開始，而在JSONPath中是從0開始

JSONPath在線練習網址：http://jsonpath.com/

25.3.4 JSONPath用法

其基本用法形式如下所示：

jsonPath(obj, expr [, args])

基參數如下所示：

obj (object|array):

JSON數據對象

expr (string):

JSONPath表達式

args (object|undefined):

改變輸出格式，比如是輸出是值還是路徑，

args.resultType可選的輸出格式爲："VALUE"、"PATH"、"IPATH"

返回類型爲(array|false):

若返回array，則代表成功匹配到數據，false則代表未匹配到數據。

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
            }
        }
}

#  獲取book節點中所有author
getAllBookAuthor=jsonpath(data,"$.store.book[*].author")
print(f"getAllBookAuthor is :{json.dumps(getAllBookAuthor,indent=4)}")
#  獲取book節點中所有author
getAllAuthor=jsonpath(data,"$..author")
print(f"getAllAuthor is {json.dumps(getAllAuthor,indent=4)}")
#  獲取store的元素，包含book和bicycle
getAllStoreElement=jsonpath(data,"$.store.*")
print(f"getAllStoreElement is {json.dumps(getAllStoreElement,indent=4)}")
# 獲取store中的所有price
getAllStorePriceA=jsonpath(data,"$[store]..price")
getAllStorePriceB=jsonpath(data,"$.store..price")
print(f"getAllStorePrictA is {getAllStorePriceA}\ngetAllStorePriceB is {getAllStorePriceB}")
# 獲取第三本書所有信息
getThirdBookInfo=jsonpath(data,"$..book[2]")
print(f"getThirdBookInfo is {json.dumps(getThirdBookInfo,indent=4)}")
# 獲取最後一本書的信息
getLastBookInfo=jsonpath(data,"$..book[-1:]")
print(f"getLastBookInfo is {json.dumps(getLastBookInfo,indent=4)}")
# 獲取前面的兩本書
getFirstAndSecondBookInfo=jsonpath(data,"$..book[:2]")
print(f"getFirstAndSecondBookInfo is {json.dumps(getFirstAndSecondBookInfo,indent=4)}")
#  根據isbn進行過濾
getWithFilterISBN=jsonpath(data,"$..book[?(@.isbn)]")
print(f"getWithFilterISBN is {json.dumps(getWithFilterISBN,indent=4)}")
# 根據price進行篩選
getWithFilterPrice=jsonpath(data,"$..book[?(@.price<10)]")
print(f"getWithFilterPrice is {json.dumps(getWithFilterPrice,indent=4)}")
# 所有元素
getAllElement=jsonpath(data,"$..*")
print(f"getAllElement is {json.dumps(getAllElement,indent=4)}")
# 未能匹配到元素時
noMatchElement=jsonpath(data,"$..surpass")
print(f"noMatchElement is {noMatchElement}")
# 調整輸出格式
controlleOutput=jsonpath(data,expr="$..author",result_type="PATH")
print(f"controlleOutput is {json.dumps(controlleOutput,indent=4)}")

最終輸出結果如下揚塵：

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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