如何在Python中访问Chrome性能日志的嵌套字典？

问题背景 #

在Python中处理Chrome性能日志时，需要访问日志嵌套结构里的method和params字段。最初直接通过message['method']访问时触发TypeError: string indices must be integers，原因是log["message"]实际是JSON字符串而非字典结构。通过json.loads解析字符串后已成功获取目标数据，但不确定当前方案是否最优，寻求技术优化指导。

原尝试代码 #

def new_file_log(self):
    # Chrome log
    logs = self.driver.get_log("performance")
    for log in logs:
        message = log["message"]
        if 'Network.responseReceived' in message:
            print(f"{message}")
            # print(f"message['method']")

错误信息 #

TypeError: string indices must be integers

日志示例 #

{'message': {'method': 'Network.responseReceived', 'params': {...}}}

现有解决方案代码 #

def new_file_log(self):
    logs = self.driver.get_log("performance")

    for log in logs:
        message = json.loads(log["message"])["message"]
        if "Network.responseReceived" == message["method"]:
            print(f"{message['method']}")
            print(f"{message['params']}")
            print(f"{message['params']['response']['url']}")
            print(' ')

优化指导 #

你的解决方案核心思路是正确的——必须将JSON字符串解析为字典才能访问嵌套字段，以下是几个优化方向：

1. 添加异常处理
   避免因日志格式异常导致程序崩溃，比如JSON解析失败、字段缺失的情况：

   import json
   
   def new_file_log(self):
       logs = self.driver.get_log("performance")
       for log in logs:
           try:
               parsed_log = json.loads(log["message"])
               message = parsed_log["message"]
               if message["method"] == "Network.responseReceived":
                   print(f"{message['method']}")
                   print(f"{message['params']}")
                   response = message["params"].get("response")
                   if response:
                       print(f"{response['url']}")
                   print(' ')
           except (json.JSONDecodeError, KeyError) as e:
               # 可记录错误日志或直接跳过无效日志
               continue
   

2. 提前过滤日志减少解析次数
   在解析前先通过字符串匹配过滤掉无关日志，减少不必要的JSON解析操作，提升效率：

   def new_file_log(self):
       logs = self.driver.get_log("performance")
       target_method = "Network.responseReceived"
       for log in logs:
           msg_str = log["message"]
           if target_method not in msg_str:
               continue
           try:
               parsed_log = json.loads(msg_str)
               message = parsed_log["message"]
               if message["method"] == target_method:
                   print(f"{message['method']}")
                   print(f"{message['params']}")
                   print(' ')
           except (json.JSONDecodeError, KeyError):
               continue
   

3. 简化代码结构（Python3.8+）
   使用海象运算符:=减少变量重复定义，让代码更紧凑：

   def new_file_log(self):
       logs = self.driver.get_log("performance")
       target_method = "Network.responseReceived"
       for log in logs:
           if target_method in log["message"] and (parsed := json.loads(log["message"])):
               message = parsed["message"]
               if message["method"] == target_method:
                   print(f"{message['method']}")
                   print(f"{message['params']}")
                   print(' ')
   

4. 批量解析与处理
   如果日志量较大，可先批量解析有效日志，再进行过滤处理，适合需要多次访问日志字段的场景：

   def new_file_log(self):
       logs = self.driver.get_log("performance")
       # 批量解析有效日志
       parsed_logs = []
       for log in logs:
           try:
               parsed = json.loads(log["message"])
               parsed_logs.append(parsed["message"])
           except (json.JSONDecodeError, KeyError):
               continue
       # 过滤目标日志并处理
       target_method = "Network.responseReceived"
       for message in parsed_logs:
           if message["method"] == target_method:
               print(f"{message['method']}")
               print(f"{message['params']}")
               print(' ')
   

内容的提问来源于stack exchange，提问作者ghost239