python logging 确保只添加一次处理程序

Question

我有一段代码正在初始化一个记录器，如下所示。

logger = logging.getLogger()
hdlr = logging.FileHandler('logfile.log')
formatter = logging.Formatter('%(asctime)s %(levelname)s %(message)s')
hdlr.setFormatter(formatter)
logger.addHandler(hdlr) 
logger.setLevel(logging.DEBUG)

不幸的是，这段代码被多次调用，有什么方法可以检查处理程序是否已经存在 - 我更愿意在不必使用 Singleton 的情况下实现它。

编辑:抱歉，忘了提到这是在 python 2.5 上 - 干杯，理查德

Answer 1

作为@offbyone 评论，可以将冗余处理程序添加到记录器的同一实例。 python docs for logging说-

"Multiple calls to getLogger() with the same name will return a reference to the same logger object."

所以我们不必担心将实现变成单例，因为它已经是。

不幸的是，与同一记录器实例关联的处理程序不正确。 可能附加了重复的处理程序。

例子-

1. 复制这段代码并保存在main.py中

   import logging
   print 'inside main.py',
   print '-'*50
   def logger():
   
         print 'initializing logger....'
         logPath = '.'
         fileName = 'temp'
   
         # configure log formatter
         logFormatter = logging.Formatter("%(asctime)s [%(filename)s] [%(funcName)s] [%(levelname)s] [%(lineno)d] %(message)s")
   
         # configure file handler
         fileHandler = logging.FileHandler("{0}/{1}.log".format(logPath, fileName))
         fileHandler.setFormatter(logFormatter)
   
         # configure stream handler
         consoleHandler = logging.StreamHandler()
         consoleHandler.setFormatter(logFormatter)
   
         # get the logger instance
         logger = logging.getLogger(__name__)
   
         # set the logging level
         logger.setLevel(logging.DEBUG)
   
         print 'adding handlers- '
   
         #if not len(logger.handlers):
         logger.addHandler(fileHandler)
         logger.addHandler(consoleHandler)
   
         print 'logger initialized....\n'
         print 'associated handlers - ', len(logger.handlers)
         for handler in logger.handlers:
               print handler
         print
         return logger
   
   main_logger = logger()
   main_logger.info('utilizing main.py logger.')
   print 'exiting main.py',
   print '-'*50
   

2. 以及sub.py中的如下代码

   print 'inside sub.py',
   print '-'*50
   print 'importing main.py'
   import main
   print 'imported main.py'
   import logging
   print 'getting logger instance in sub'
   sub_logger = main.logger()
   print 'got logger instance in sub'
   sub_logger.info("utilizing sub_logger")
   print 'exiting sub.py',
   print '-'*50
   

3. 运行 sub.py

   narayan@y510p:~/code/so$ python sub.py
   inside sub.py --------------------------------------------------
   importing main.py
   inside main.py --------------------------------------------------
   initializing logger....
   adding handlers- 
   logger initialized....
   
   associated handlers -  2
   <logging.FileHandler object at 0x7f7158740c90>
   <logging.StreamHandler object at 0x7f7158710b10>
   
   2015-08-04 07:41:01,824 [main.py] [<module>] [INFO] [41] utilizing main.py logger.
   exiting main.py --------------------------------------------------
   imported main.py
   getting logger instance in sub
   initializing logger....
   adding handlers- 
   logger initialized....
   
   associated handlers -  4 # <===== 4 handlers (duplicates added)
   <logging.FileHandler object at 0x7f7158740c90>
   <logging.StreamHandler object at 0x7f7158710b10>
   <logging.FileHandler object at 0x7f7158710bd0>
   <logging.StreamHandler object at 0x7f7158710c10>
   
   got logger instance in sub
   2015-08-04 07:41:01,824 [sub.py] [<module>] [INFO] [10] utilizing sub_logger
   2015-08-04 07:41:01,824 [sub.py] [<module>] [INFO] [10] utilizing sub_logger
   exiting sub.py --------------------------------------------------
   

因此，多次调用返回相同记录器的方法会添加重复的处理程序。

现在，你的问题-

is there any way I can check to see if the handler already exists

是的，有-

logger.handlers 返回与给定 logger 关联的所有处理程序的列表。

在将处理程序添加到记录器的实例之前，请确保不要添加重复的处理程序 在 main.py 中，取消注释 if not len(logger.handlers): 的行并正确缩进以下两行 -

if not len(logger.handlers):
    logger.addHandler(fileHandler)
    logger.addHandler(consoleHandler)

现在再次运行 sub.py

narayan@y510p:~/code/so$ python sub.py
inside sub.py --------------------------------------------------
importing main.py
inside main.py --------------------------------------------------
initializing logger....
adding handlers- 
logger initialized....

associated handlers -  2
<logging.FileHandler object at 0x7fd67a891c90>
<logging.StreamHandler object at 0x7fd67a862b10>

2015-08-04 08:14:45,620 [main.py] [<module>] [INFO] [41] utilizing main.py logger.
exiting main.py --------------------------------------------------
imported main.py
getting logger instance in sub
initializing logger....
adding handlers- 
logger initialized....

associated handlers -  2 # <===== Still 2 handlers (no duplicates)
<logging.FileHandler object at 0x7fd67a891c90>
<logging.StreamHandler object at 0x7fd67a862b10>

got logger instance in sub
2015-08-04 08:14:45,620 [sub.py] [<module>] [INFO] [10] utilizing sub_logger
exiting sub.py --------------------------------------------------

此外，如果您想限制要添加到记录器实例的处理程序的类型，您可以执行以下操作-

    print 'adding handlers- '
    # allows to add only one instance of file handler and stream handler
    if len(logger.handlers) > 0:
        print 'making sure we do not add duplicate handlers'
        for handler in logger.handlers:
              # add the handlers to the logger
              # makes sure no duplicate handlers are added

              if not isinstance(handler, logging.FileHandler) and not isinstance(handler, logging.StreamHandler):
                    logger.addHandler(fileHandler)
                    print 'added file handler'
                    logger.addHandler(consoleHandler)
                    print 'added stream handler'
    else:
        logger.addHandler(fileHandler)
        logger.addHandler(consoleHandler)
        print 'added handlers for the first time'

希望这会有所帮助!

编辑:

Unfortunately the same is not true for the handlers associated with the same instance of the logger. There can be duplicate handlers attached.

事实证明，上述说法并不完全正确。

假设我们在主模块中创建并配置了一个名为 'main_logger' 的记录器(它只是配置记录器，不返回任何内容)。

# get the logger instance
logger = logging.getLogger("main_logger")
# configuration follows
...

现在在子模块中，如果我们按照命名层次'main_logger.sub_module_logger'创建一个子记录器，我们不需要在子模块中配置它。只需按照命名层次结构创建记录器就足够了。

# get the logger instance
logger = logging.getLogger("main_logger.sub_module_logger")
# no configuration needed
# it inherits the configuration from the parent logger
...

它也不会添加重复的处理程序。

引用- Using logging in multiple modules