如何用Python优化JSON数组中按Key取值的代码（替代多IF）

问题背景 #

你有Google Admin Reports格式的JSON使用报告数据，需要提取指定name字段对应的各类*Value值。当前通过多个if语句匹配字段名的方式实现，代码冗余且不易维护，希望得到更简洁的优化方案。

原始JSON数据示例 #

{
  "kind": "admin#reports#usageReport",
  "date": "2022-07-17",
  "etag": "\"dng2uCItaXPqmMj2MG4RUqVkRjnE_4kf0VvQ0_WkiTg/dICFK4HeNet7m-jGyh4UpD7jLI4\"",
  "entity": {
    "type": "USER",
    "customerId": "H01234sux",
    "userEmail": "harry.potter@hogwarts.edu",
    "profileId": "123456789999012345678"
  },
  "parameters": [
    {
      "name": "gmail:last_access_time",
      "datetimeValue": "2022-07-08T00:06:16.000Z"
    },
    {
      "name": "gmail:num_emails_exchanged",
      "intValue": "0"
    },
    {
      "name": "accounts:first_name",
      "stringValue": "Harry"
    },
    {
      "name": "accounts:last_name",
      "stringValue": "Potter"
    },
    {
      "name": "accounts:is_disabled",
      "boolValue": false
    },
    {
      "name": "accounts:disabled_reason"
    },
    {
      "name": "accounts:creation_time",
      "datetimeValue": "2022-05-26T21:54:18.000Z"
    },
    {
      "name": "accounts:last_login_time",
      "datetimeValue": "1970-01-01T00:00:00.000Z"
    },
    {
      "name": "accounts:is_super_admin",
      "boolValue": false
    },
    {
      "name": "accounts:is_delegated_admin",
      "boolValue": false
    },
    {
      "name": "accounts:drive_used_quota_in_mb",
      "intValue": "0"
    }
  ]
}

原始实现代码 #

for user in users:
    uemail = user['entity']['userEmail'];
    for param in user['parameters']:
        if param['name'] == 'gmail:last_webmail_time':
            lwmtm = param['datetimeValue'];
        if param['name'] == 'accounts:total_quota_in_mb':
            ttlqmb = param['intValue']
        if param['name'] == 'accounts:used_quota_in_mb':
            usqmb = param['intValue']
    print(u'{0}, {1}, {2}, {3}, {4}, {5}, {6}, {7}, {8}, {9}, {10}, {11}, {12}'.format(uemail,lwmtm,lintm,lactm,acdstr,accrtm,aclltm,aclstm,drusmb,gmusmb,gpusmb,ttlqmb,usqmb))

优化实现方案 #

方案1：将参数列表转为字典（基础版） #

核心思路是把每个用户的parameters列表转换为以name为键、对应*Value为值的字典，后续直接通过键名取值，彻底替代多if判断：

for user in users:
    uemail = user['entity']['userEmail']
    # 构建参数字典：自动匹配所有带Value后缀的字段值
    param_dict = {}
    for param in user['parameters']:
        # 提取参数中的值（兼容datetime/int/string/bool等类型）
        value = next((v for k, v in param.items() if k.endswith('Value')), None)
        param_dict[param['name']] = value
    
    # 通过get方法获取参数，可设置默认值避免KeyError或变量未定义
    lwmtm = param_dict.get('gmail:last_webmail_time', '')
    ttlqmb = param_dict.get('accounts:total_quota_in_mb', '0')
    usqmb = param_dict.get('accounts:used_quota_in_mb', '0')
    # 补充其他需要提取的参数，示例：
    lintm = param_dict.get('xxx:xxx_field', '')
    lactm = param_dict.get('yyy:yyy_field', '')
    acdstr = param_dict.get('accounts:disabled_reason', '')
    accrtm = param_dict.get('accounts:creation_time', '')
    aclltm = param_dict.get('accounts:last_login_time', '')
    aclstm = param_dict.get('accounts:is_super_admin', False)
    drusmb = param_dict.get('accounts:drive_used_quota_in_mb', '0')
    gmusmb = param_dict.get('gmail:num_emails_exchanged', '0')
    gpusmb = param_dict.get('xxx:other_gmail_param', '')
    
    # 格式化输出（使用f-string更简洁）
    print(f"{uemail}, {lwmtm}, {lintm}, {lactm}, {acdstr}, {accrtm}, {aclltm}, {aclstm}, {drusmb}, {gmusmb}, {gpusmb}, {ttlqmb}, {usqmb}")

方案2：预定义参数映射（进阶版） #

如果需要提取的参数固定，可以预先定义参数列表和默认值，批量处理提取逻辑，进一步提升可维护性：

# 预定义需要提取的参数：键为参数name，值为默认值
REQUIRED_PARAMS = {
    'gmail:last_webmail_time': '',
    'accounts:total_quota_in_mb': '0',
    'accounts:used_quota_in_mb': '0',
    'xxx:xxx_field': '',
    'yyy:yyy_field': '',
    'accounts:disabled_reason': '',
    'accounts:creation_time': '',
    'accounts:last_login_time': '',
    'accounts:is_super_admin': False,
    'accounts:drive_used_quota_in_mb': '0',
    'gmail:num_emails_exchanged': '0',
    'xxx:other_gmail_param': ''
}

for user in users:
    uemail = user['entity']['userEmail']
    # 构建参数字典
    param_dict = {
        p['name']: next((v for k, v in p.items() if k.endswith('Value')), None)
        for p in user['parameters']
    }
    
    # 合并默认值与实际提取的值
    extracted_params = {k: param_dict.get(k, v) for k, v in REQUIRED_PARAMS.items()}
    
    # 按顺序组装输出内容
    output_values = [uemail] + list(extracted_params.values())
    print(', '.join(map(str, output_values)))

方案优势 #

• 简洁性：消除大量重复的if判断，代码结构更清晰
• 健壮性：通过get方法设置默认值，避免因参数缺失导致的KeyError或变量未定义问题
• 可维护性：后续新增或修改提取参数时，只需调整字典配置，无需修改循环逻辑

内容的提问来源于stack exchange，提问作者Venkat5121