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Python 日志打印之自定义logger handler

日志打印之自定义logger handler

By:授客 QQ1033553122

#实践环境

WIN 10

Python 3.6.5

#实践代码

handler.py

#!/usr/bin/env python# -*- coding:utf-8 -*-\'\'\'@Author : shouke\'\'\'import loggingimport logging.configclass MyLogHandler(logging.Handler, object):\"\"\"自定义日志handler\"\"\"def __init__(self, name, other_attr=None, **kwargs):logging.Handler.__init__(self)print(\'初始化自定义日志处理器:\', name)print(\'其它属性值:\', other_attr)def emit(self, record):\"\"\"emit函数为自定义handler类时必重写的函数,这里可以根据需要对日志消息做一些处理,比如发送日志到服务器发出记录(Emit a record)\"\"\"try:msg = self.format(record)print(\'获取到的消息为:\', msg)for item in dir(record):if item in [\'process\', \'processName\', \'thread\', \'threadName\']:print(item, \':\', getattr(record, item))except Exception:self.handleError(record)# 测试logging.basicConfig()logger = logging.getLogger(\"logger\")logger.setLevel(logging.INFO)my_log_handler = MyLogHandler(\'LoggerHandler\')logger.addHandler(my_log_handler)logger.info(\'hello,shouke\')运行handler.py,结果输出如下初始化自定义日志处理器: LoggerHandler其它属性值: None获取到的消息为: hello,shoukeprocess : 27932processName : MainProcessthread : 45464threadName : MainThreadINFO:logger:hello,shouke

  

#通过字典配置添加自定义handler

mytest.py(与handler.py位于同一层级目录)

#!/usr/bin/env python# -*- coding:utf-8 -*-### \'\'\'# @CreateTime: 2020/12/29 14:08# @Author : shouke# \'\'\'#import loggingimport logging.configLOGGING_CONFIG = {\"version\": 1,\"disable_existing_loggers\": False,\"formatters\": {\"default\": {\"format\":\"%(asctime)s %(filename)s %(lineno)s %(levelname)s : %(message)s\",},\"plain\": {\"format\": \"%(message)s\",}},\"handlers\": {\"customer_handler\":{\"class\":\"study.MyLogHandler\",\"formatter\":\"default\",# 注意,class,formatter,level,filters之外的参数将默认传递给由class指定类的构造函数\"name\":\"LoggerHandler\",\"other_attr\":\"something others\"},\"console\": {\"class\": \"logging.StreamHandler\",\"formatter\": \"default\",},},\"loggers\": {\"customer_logger\":{\"handlers\": [\"customer_handler\", \"console\"],\"level\": logging.INFO,\"propagate\": False,}}}logging.config.dictConfig(LOGGING_CONFIG)logger = logging.getLogger(\'customer_logger\')logger.info(\'hello,shouke\')运行mytest.py,输出结果如下初始化自定义日志处理器: LoggerHandler其它属性值: something others获取到的消息为: 2021-01-01 17:51:54,661 mytest.py 48 INFO : hello,shoukeprocess : 36280processName : MainProcessthread : 37316threadName : MainThreadINFO:logger:hello,shouke2021-01-01 17:51:54,661 mytest5.py 48 INFO : hello,shouke。

  

##问题:为什么mytest.py中的代码,不能放在study.py中?

如下,在study.py模块,MyLogHandler类之后追加下述代码

LOGGING_CONFIG = {\"version\": 1,\"disable_existing_loggers\": False,\"formatters\": {\"default\": {\"format\":\"%(asctime)s %(filename)s %(lineno)s %(levelname)s : %(message)s\",}},\"handlers\": {\"customer_handler\":{\"class\":\"study.MyLogHandler\",\"formatter\":\"default\",\"name\":\"LoggerHandler\",\"other_attr\":\"something others\"}},\"loggers\": {\"customer_logger\":{\"handlers\": [\"customer_handler\"],\"level\": logging.INFO,\"propagate\": False,}}}logging.config.dictConfig(LOGGING_CONFIG)logger = logging.getLogger(\'customer_logger\')logger.info(\'hello,shouke\')运行mytest.py,输出结果如下初始化自定义日志处理器: LoggerHandler其它属性值: something others获取到的消息为: 2021-01-09 10:48:24,090 study.py 66 INFO : hello,shoukeprocess : 17276processName : MainProcessthread : 14516threadName : MainThread初始化自定义日志处理器: LoggerHandler其它属性值: something others获取到的消息为: 2021-01-09 10:48:24,090 study.py 66 INFO : hello,shoukeprocess : 17276processName : MainProcessthread : 14516threadName : MainThread

  

如上,可以看到,自定义类构造函数被重复执行,日志消息被重复处理

##原因分析

logging.config.dictConfig(config)函数内部调用了DictConfigurator(config).configure(),而configure函数内DictConfigurator部,根据incremental,handlers等当前日志配置,被执行的分支代码中,会调用

DictConfigurator类实例的configure_handler()方法,该方法中,根据当前配置,又会再次调用DictConfigurator类实例的resolve(self, s)方法,参数s接收handler中class配置项目的值。具体代码如下:

class DictConfigurator(BaseConfigurator):# ... 略def resolve(self, s):\"\"\"Resolve strings to objects using standard import and attributesyntax.\"\"\"name = s.split(\'.\') # 本例中,s为study.MyLogHandlerused = name.pop(0)  # used 为studytry:found = self.importer(used) # 这里importer = staticmethod(__import__) # 所以此处代码等同于__import__(used) # 这里导入自定义日志处理器所在模块会导致模块中的logging.config.dictConfig(config)代码再次被执行for frag in name:used += \'.\' + fragtry:found = getattr(found, frag)except AttributeError:self.importer(used)found = getattr(found, frag)return foundexcept ImportError:e, tb = sys.exc_info()[1:]v = ValueError(\'Cannot resolve %r: %s\' % (s, e))v.__cause__, v.__traceback__ = e, tbraise vdef configure_formatter(self, config):\"\"\"Configure a formatter from a dictionary.\"\"\"if \'()\' in config:factory = config[\'()\'] # for use in exception handlertry:result = self.configure_custom(config)except TypeError as te:if \"\'format\'\" not in str(te):raise#Name of parameter changed from fmt to format.#Retry with old name.#This is so that code can be used with older Python versions#(e.g. by Django)config[\'fmt\'] = config.pop(\'format\')config[\'()\'] = factoryresult = self.configure_custom(config)else:fmt = config.get(\'format\', None)dfmt = config.get(\'datefmt\', None)style = config.get(\'style\', \'%\')cname = config.get(\'class\', None)if not cname:c = logging.Formatterelse:c = _resolve(cname)result = c(fmt, dfmt, style)return result# ... 略def configure_handler(self, config):\"\"\"Configure a handler from a dictionary.\"\"\"config_copy = dict(config)  # for restoring in case of errorformatter = config.pop(\'formatter\', None)if formatter:try:formatter = self.config[\'formatters\'][formatter]except Exception as e:raise ValueError(\'Unable to set formatter \'\'%r: %s\' % (formatter, e))level = config.pop(\'level\', None)filters = config.pop(\'filters\', None)if \'()\' in config:c = config.pop(\'()\')if not callable(c):c = self.resolve(c)factory = celse:cname = config.pop(\'class\')klass = self.resolve(cname)#Special case for handler which refers to another handlerif issubclass(klass, logging.handlers.MemoryHandler) and\\\'target\' in config:try:th = self.config[\'handlers\'][config[\'target\']]if not isinstance(th, logging.Handler):config.update(config_copy)  # restore for deferred cfgraise TypeError(\'target not configured yet\')config[\'target\'] = thexcept Exception as e:raise ValueError(\'Unable to set target handler \'\'%r: %s\' % (config[\'target\'], e))elif issubclass(klass, logging.handlers.SMTPHandler) and\\\'mailhost\' in config:config[\'mailhost\'] = self.as_tuple(config[\'mailhost\'])elif issubclass(klass, logging.handlers.SysLogHandler) and\\\'address\' in config:config[\'address\'] = self.as_tuple(config[\'address\'])factory = klassprops = config.pop(\'.\', None)kwargs = dict([(k, config[k]) for k in config if valid_ident(k)])try:result = factory(**kwargs)except TypeError as te:if \"\'stream\'\" not in str(te):raise#The argument name changed from strm to stream#Retry with old name.#This is so that code can be used with older Python versions#(e.g. by Django)kwargs[\'strm\'] = kwargs.pop(\'stream\')result = factory(**kwargs)if formatter:result.setFormatter(formatter)if level is not None:result.setLevel(logging._checkLevel(level))if filters:self.add_filters(result, filters)if props:for name, value in props.items():setattr(result, name, value)return result

  

至此,logging.config.dictConfig(config)放自定义日志处理类模块中,导致自定义日志处理类重复被执行的原因已经清楚了。

configure函数内部,根据incremental,handlers等当前日志配置,被执行的分支代码中,也可能执行DictConfigurator类实例的configure_formatter()方法,类似的,该方法中也会调用一个名为_resolve的方法,具体代码如下

def _resolve(name):\"\"\"Resolve a dotted name to a global object.\"\"\"name = name.split(\'.\')used = name.pop(0)found = __import__(used)for n in name:used = used + \'.\' + ntry:found = getattr(found, n)except AttributeError:__import__(used)found = getattr(found, n)return found

  

如果自定义Formatter,把logging.config.dictConfig(config)放自定义日志格式化类模块中,也可能导致重复执行

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