如何用Python调用JSON中的userid值？附JSON结构优化建议

问题 #

现有如下结构的JSON文件：

{
    "item": {
        "userid":"",
        "subitem": {
            "object0":"",
            "object0times":"",
            "object1":"",
            "object1times":"",
            "object2":"",
            "object2times":""
        }
    },
    "item1": {
        "userid":"",
        "subitem": {
            "object0":"",
            "object0times":"",
            "object1":"",
            "object1times":"",
            "object2":"",
            "object2times":""
        }
    }
}

尝试用以下Python代码读取userid值时触发KeyError：

with open('dictionary.json') as f:
        d = json.load(f)
        print(d[userid])

错误信息：

discord.ext.commands.errors.CommandInvokeError: Command raised an exception: KeyError: 'userid'

已知userid是item/item1的子层级键，需要解决正确读取目标值的方法，以及优化JSON结构提升检索速度的方案。

解决方法 #

1. 正确读取层级值 #

错误根源是直接访问顶层的userid键，但它实际存在于item和item1的子结构中，且代码中userid未加引号（作为字符串键需用引号包裹）。

• 读取单个userid：

  import json
  
  with open('dictionary.json') as f:
      d = json.load(f)
      # 读取item下的userid
      print(d['item']['userid'])
      # 读取item1下的userid
      print(d['item1']['userid'])
      # 读取subitem下的具体object值，比如object0
      print(d['item']['subitem']['object0'])
  

• 遍历所有顶层对象的userid：
  如果后续有更多类似item/item1的键，可循环遍历顶层键批量获取：

  import json
  
  with open('dictionary.json') as f:
      d = json.load(f)
      for top_key in d:
          print(d[top_key]['userid'])
          print(d[top_key]['subitem']['object1times'])
  

2. 优化JSON结构提升检索效率 #

当前用item/item1作为顶层键的结构，不利于按userid快速检索，可根据使用场景调整：

方案一：用数组存储用户对象

适合批量处理或用户数量动态变化的场景，检索时可快速定位目标用户：

{
    "users": [
        {
            "userid": "user_001",
            "subitem": {
                "object0": "",
                "object0times": "",
                "object1": "",
                "object1times": "",
                "object2": "",
                "object2times": ""
            }
        },
        {
            "userid": "user_002",
            "subitem": {
                "object0": "",
                "object0times": "",
                "object1": "",
                "object1times": "",
                "object2": "",
                "object2times": ""
            }
        }
    ]
}

读取指定userid的示例：

import json

target_userid = "user_001"
with open('dictionary.json') as f:
    d = json.load(f)
    # 快速匹配目标用户
    target_user = next(user for user in d['users'] if user['userid'] == target_userid)
    print(target_user['subitem']['object0times'])

方案二：用userid作为顶层键

适合频繁通过userid直接访问数据的场景，检索时间复杂度为O(1)：

{
    "user_001": {
        "subitem": {
            "object0": "",
            "object0times": "",
            "object1": "",
            "object1times": "",
            "object2": "",
            "object2times": ""
        }
    },
    "user_002": {
        "subitem": {
            "object0": "",
            "object0times": "",
            "object1": "",
            "object1times": "",
            "object2": "",
            "object2times": ""
        }
    }
}

读取指定userid的示例：

import json

target_userid = "user_001"
with open('dictionary.json') as f:
    d = json.load(f)
    # 直接通过userid访问对应数据
    print(d[target_userid]['subitem']['object2'])

内容的提问来源于stack exchange，提问作者gallmonds