Python JSONPath示例

什么是JSONPath？ (What is JSONPath?)

JSONPath is an expression language to parse JSON data. It’s very similar to the XPath expression language to parse XML data.

JSONPath是一种用于解析JSON数据的表达语言。与解析XML数据的XPath表达式语言非常相似。

The idea is to parse the JSON data and get the value you want. This is more memory efficient because we don’t need to read the complete JSON data.

想法是解析JSON数据并获取所需的值。由于不需要读取完整的JSON数据，因此内存使用效率更高。

Python JSONPath库 (Python JSONPath Libraries)

There are many JSONPath libraries in Python.

Python中有许多JSONPath库。

jsonpath: It’s a port of the Perl, and JavaScript versions of JSONPath.jsonpath ：这是Perl和JSONPathJavaScript版本的端口。
jsonpath-rw: The complete Python implementation of the JSONPath expressions. The JSONPath expressions are first class objects, easy to analyze, transform, parse, print, and extend. The jsonpath-rw-ext module provides some additional extensions to extend its functionalities.jsonpath-rw ：JSONPath表达式的完整Python实现。 JSONPath表达式是一流的对象，易于分析，转换，解析，打印和扩展。 jsonpath-rw-ext模块提供了一些其他扩展，以扩展其功能。
jsonpath-ng: The final implementation of the JSONPath that aims to be standard compliant, including arithmetic and binary comparison operators. This library merges jsonpath-rw and jsonpath-rw-ext modules and further enhances it.jsonpath-ng ： JSONPath的最终实现，旨在实现标准兼容，包括算术和二进制比较运算符。该库合并了jsonpath-rw和jsonpath-rw-ext模块，并对其进行了进一步增强。

使用哪个Python JSONPath库？ (Which Python JSONPath Library to Use?)

The jsonpath-ng module is the most comprehensive and written purely in Python. It supports both Python 2 and Python 3. So, we will use this module for Python JSONPath examples.

jsonpath-ng模块是最全面的模块，仅用 Python编写。它同时支持Python 2和Python3。因此，我们将该模块用于Python JSONPath示例。

安装jsonpath-ng模块 (Installing jsonpath-ng Module)

We can install jsonpath-ng module using PIP.

我们可以使用PIP安装jsonpath-ng模块。

$ pip3.7 install jsonpath-ng

Python jsonpath-ng Install

Python jsonpath-ng安装

使用JSONPath解析简单的JSON数据 (Parsing a Simple JSON Data using JSONPath)

Let’s look at a simple example to parse the JSON data and get the required attribute value.

让我们看一个简单的示例，解析JSON数据并获取所需的属性值。

import jsonfrom jsonpath_ng import jsonpath, parsejson_string = '{"id":1, "name":"Pankaj"}'
json_data = json.loads(json_string)jsonpath_expression = parse('$.id')match = jsonpath_expression.find(json_data)print(match)
print("id value is", match[0].value)

Output:

输出：

[DatumInContext(value=1, path=Fields('id'), context=DatumInContext(value={'id': 1, 'name': 'Pankaj'}, path=Root(), context=None))]
id value is 1

We are using json module to convert the JSON string to a dictionary.

我们正在使用json模块将JSON字符串转换为字典。

使用JSONPath表达式解析列表 (Parsing a List using JSONPath Expression)

The JSON key can contain a list of values. We can use JSONPath expression to parse the list and get the list of values.

JSON密钥可以包含值列表。我们可以使用JSONPath表达式来解析列表并获取值列表。

Let’s say we have a JSON file “db.json” with the following contents.

假设我们有一个包含以下内容的JSON文件“ db.json”。

{"employees": [{"id": 1,"name": "Pankaj","salary": "10000"},{"name": "David","salary": "5000","id": 2}]
}

We want to parse this JSON file and get the list of employee ids. We can use JSONPath expressions to get this data very easily.

我们要解析此JSON文件并获取员工ID列表。我们可以使用JSONPath表达式非常轻松地获取此数据。

import json
from jsonpath_ng import jsonpath, parsewith open("db.json", 'r') as json_file:json_data = json.load(json_file)print(json_data)jsonpath_expression = parse('employees[*].id')for match in jsonpath_expression.find(json_data):print(f'Employee id: {match.value}')

Output:

输出：

{'employees': [{'id': 1, 'name': 'Pankaj', 'salary': '10000'}, {'name': 'David', 'salary': '5000', 'id': 2}]}
Employee id: 1
Employee id: 2

Python f-strings – PEP 498 – Literal String InterpolationPython f字符串– PEP 498 –文字字符串插值

If you want to get the data into a list, you can use Python list comprehension.

如果要将数据放入列表中，可以使用Python list comprehension 。

emp_ids_list = [match.value for match in jsonpath_expression.find(json_data)]
print(emp_ids_list)  # [1, 2]

结论 (Conclusion)

JSONPath provides us an easy way to parse the JSON data and extract specific values. It’s very useful when the JSON data is huge and we are interested in only few of the values.

JSONPath为我们提供了一种解析JSON数据并提取特定值的简便方法。当JSON数据庞大且我们仅对其中几个值感兴趣时，此功能非常有用。

参考资料 (References)

jsonpath.com: to test the JSONPath expression validityjsonpath.com ：测试JSONPath表达式的有效性
jsonlint.com: to validate JSON datajsonlint.com ：验证JSON数据

翻译自: https://www.journaldev.com/33265/python-jsonpath-examples