Python标准库 - logging
编写代码时, 常要跟踪下其运行过程, 记录日志是常用的方式. 较简单的就是print命令打印到终端, 或通过open函数写入文件. 但随着代码量的增加, 该方式不可控的弊端, 也凸显出来, 这也正是logging模块出现的背景.对于logging模块, 简单来说直接import进来, 就可以用了.
In : import logging
In : logging.warning('Watch out!')
WARNING:root:Watch out!
In : logging.info('I told you so')
In :
In :
第二个语句没有输出呢, 这需了解下日志等级的概念. logging模块默认的日志等级是WARNING, 大于该等级的日志才会输出, 细节如下.
Level When it’s usedDEBUGDetailed information, typically of interest only when diagnosing problems.INFOConfirmation that things are working as expected.WARNINGAn indication that something unexpected happened, or indicative of some problem in the near future (e.g. ‘disk space low’). The software is still working as expected.ERRORDue to a more serious problem, the software has not been able to perform some function.CRITICALA serious error, indicating that the program itself may be unable to continue running. 借助basicConfig方法, 可对日志记录做些配置.
In : import logging
In : logging.basicConfig(filename='/tmp/example.log',level=logging.DEBUG)
In : logging.debug('This message should go to the log file')
In : logging.info('So should this')
In : logging.warning('And this, too')
$ cat /tmp/example.log
DEBUG:root:This message should go to the log file
INFO:root:So should this
WARNING:root:And this, too
在脚本中, 可按照下面的方式使用logging模块.
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# myapp.py
import logging
import mylib
def main():
logging.basicConfig(filename='myapp.log', format='%(asctime)s - %(name)s - %(levelname)s - %(pathname)s - %(message)s', level=logging.INFO)
logging.info('Started')
mylib.do_something()
logging.info('Finished')
if __name__ == '__main__':
main()
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# mylib.py
import logging
def do_something():
logging.info('Doing something')
$ python myapp.py
$ cat myapp.log
2018-01-19 17:00:14,821 - root - INFO - myapp.py - Started
2018-01-19 17:00:14,821 - root - INFO - /home/zz/stage/mylib.py - Doing something
2018-01-19 17:00:14,821 - root - INFO - myapp.py - Finished
简单了解了logging模块的使用, 接着看下其中几个重要的概念.
1. Logger 日志记录器, 暴露给应用程序直接使用的接口, 几个方法用于设置记录器.
Logger.setLevel() - 指定日志记录器处理的日志最低级别.
Logger.addHandler(), Logger.removeHandler() - 为日志记录器添加, 或移除处理器.
2. Handler 处理器, 将记录器获取的日志, 传送到其定义的目的地, 也有几个方法设置处理器.
setLevel() - 指定处理器处理的日志最低级别.
setFormatter() - 为处理器选择一个格式化器.
3. Formatter 格式化器, 指定日志的输出格式.
最开始说了logging模块的简单用法, 以及了解了上面的概念后, 看下开发较大应用时, 如何使用logging呢.
这主要介绍两种方式, 其一是, 将logging模块的配置直接写在应用代码中, 如下所示.
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# simple_logging_module.py
import logging
# create logger
logger = logging.getLogger('simple_example')
logger.setLevel(logging.DEBUG)
# create console handler and set level to debug
ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG)
# create formatter
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
# add formatter to ch
ch.setFormatter(formatter)
# add ch to logger
logger.addHandler(ch)
# 'application' code
logger.debug('debug message')
logger.info('info message')
logger.warn('warn message')
logger.error('error message')
logger.critical('critical message')
$ python simple_logging_module.py
2018-01-19 21:41:58,180 - simple_example - DEBUG - debug message
2018-01-19 21:41:58,180 - simple_example - INFO - info message
2018-01-19 21:41:58,180 - simple_example - WARNING - warn message
2018-01-19 21:41:58,180 - simple_example - ERROR - error message
2018-01-19 21:41:58,180 - simple_example - CRITICAL - critical message
其二, 配置信息写入文件中, 借助fileConfig方法加载该文件, 如下所示.
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# simple_logging_config.py
import logging
import logging.config
logging.config.fileConfig('logging.conf')
# create logger
logger = logging.getLogger('simpleExample')
# 'application' code
logger.debug('debug message')
logger.info('info message')
logger.warn('warn message')
logger.error('error message')
logger.critical('critical message')
# logging.conf
keys=root,simpleExample
keys=consoleHandler
keys=simpleFormatter
level=DEBUG
handlers=consoleHandler
level=DEBUG
handlers=consoleHandler
qualname=simpleExample
propagate=0
class=StreamHandler
level=DEBUG
formatter=simpleFormatter
args=(sys.stdout,)
format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
datefmt=
$ python simple_logging_config.py
2018-01-19 21:53:46,216 - simpleExample - DEBUG - debug message
2018-01-19 21:53:46,216 - simpleExample - INFO - info message
2018-01-19 21:53:46,216 - simpleExample - WARNING - warn message
2018-01-19 21:53:46,216 - simpleExample - ERROR - error message
2018-01-19 21:53:46,216 - simpleExample - CRITICAL - critical message
最后简单说下, 如何总结一个模块, 可围绕下面三点进行说明.
1. 该模块解决的问题, 其它方法是如何做的.
2. 模块的使用, 以及核心概念(或定义).
3. 核心API的梳理.
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