使用jmespath第三方模块提取json数据

待我称王封你为后i 2022-02-03 14:43 169阅读 0赞

在工作中经常需要查找json里面的某个key的值，如果json层级太深，使用字典自带的get方法，比较麻烦。  
这里演示一下第三方模块jmespath提取json键、值。

pip install jmespath

### 一、基本操作 ###

#### 查询key对应的value ####

import jmespath
    
    source = {"a": "foo", "b": "bar", "c": "baz"}
    result = jmespath.search('b', source)
    print(repr(result))

结果：‘bar’

#### 使用.操作符 ####

source1 = {"a": {"b": {"c": {"d": "value"}}}}
    result1 = jmespath.search('a.b.c', source1)
    print(repr(result1))

结果：\{‘d’: ‘value’\}

#### 下标操作，仅用于数组 ####

source_2 = ["a", "b", "c", "d", "e", "f"]
    index_result = jmespath.search("[1]",source_2)
    print(repr(index_result))

结果：‘b’

#### 下标和.操作符混合操作 ####

source3 = {"a": {
      "b": {
        "c": [
          {"d": [0, [1, 2]]},
          {"d": [3, 4]}
        ]
      }
    }}
    result3 = jmespath.search('a.b.c[0].d[1][0]',source3)
    print(repr(result3))
    结果：1

### 二、切片 ###

source_4 = ["a", "b", "c", "d", "e", "f"]
    result4 = jmespath.search("[1:3]",source_4)
    print(repr(result4))

结果：\[‘b’, ‘c’\]

### 二、投影 ###

投影其实就是初始时定义好格式，然后按照格式的方式进行取值。  
投影主要包括以下几种：

*  List Projections列表投影
 *  Slice Projections切片投影
 *  Object Projections对象投影
 *  Flatten Projections正则投影
 *  Filter Projections过滤条件投影

**注意：取列表用\[\]，取字典用.**

# List and Slice Projections
    source5 = {
      "people": [
        {"first": "James", "last": "d"},
        {"first": "Jacob", "last": "e"},
        {"first": "Jayden", "last": "f"},
        {"missing": "different"}
      ],
      "foo": {"bar": "baz"}
    }
    result5 = jmespath.search('people[*].first', source5)
    print(result5)

结果：\[‘James’, ‘Jacob’, ‘Jayden’\]

# Object Projections
    # Whereas a list projection is defined for a JSON array, an object projection is defined for a JSON object. You can create an object projection using 
    # the * syntax.
    source6 = {
      "ops": {
        "functionA": {"numArgs": 2},
        "functionB": {"numArgs": 3},
        "functionC": {"variadic": True}
      }
    }
    result6 = jmespath.search('ops.*.numArgs', source6)
    print(repr(result6))

结果：\[3, 2\]

# Filter Projections带过滤条件投影
    # 格式[? <expression> <comparator> <expression>]
    # 支持 ==, !=, <, <=, >, >=
    # In this example we’re searching through the people array. Each element in this array contains a hash of two elements, and each value in the hash
    # is itself a hash. We’re trying to retrieve the value of the general key that contains an age key with a value above 20.
    source7 = {
      "people": [
        {
          "general": {
            "id": 100,
            "age": 20,
            "other": "foo",
            "name": "Bob"
          },
          "history": {
            "first_login": "2014-01-01",
            "last_login": "2014-01-02"
          }
        },
        {
          "general": {
            "id": 101,
            "age": 30,
            "other": "bar",
            "name": "Bill"
          },
          "history": {
            "first_login": "2014-05-01",
            "last_login": "2014-05-02"
          }
        }
      ]
    }
    result7 = jmespath.search("people[?general.age > `20`].general | [0]", source7)
    print(repr(result7))

\{‘id’: 101, ‘other’: ‘bar’, ‘age’: 30, ‘name’: ‘Bill’\}

## 更多jmspath使用方法参考： ##

## [jmespath官方API][jmespath_API] ##

[jmespath_API]: http://jmespath.org/examples.html