python Loging 入门_logning-优快云博客

初级教程

Logning 模块定义了很多方法和类，为application和libraries实现了一个灵活的事件记录系统。

什么时候使用Log:

Task you want to perform	The best tool for the task
Console 中展示	print()
程序正常运行时的事件	logging.info() (or logging.debug() for very detailed output for diagnostic purposes)
关于某个运行时事件，发出警告	warnings.warn() in library code if the issue is avoidable and the client application should be modified to eliminate the warning logging.warning() if there is nothing the client application can do about the situation, but the event should still be noted
抛出异常	Raise an exception
Report suppression of an error without raising an exception (e.g. error handler in a long-running server process)	logging.error(), logging.exception() or logging.critical() as appropriate for the specific error and application domain

log 的等级：

Level	When it’s used
DEBUG	诊断错误时候的详细信息
INFO	程序正常运行，用来确认信息
WARNING	程序正常运行，但是警告某个未来可能发生的问题，或者未预料的事情
ERROR	严重问题，某些功能无法实现
CRITICAL	严重错误，程序无法运行

默认Level 是WARNING，默认只有WARNING，ERROR, CRITICAL会被追踪。

例子：

importlogging

logging.debug("debug")
logging.info('info')
logging.warning("warning")
logging.error('error')
logging.critical("critical")

输出：

D:\software\python-2.7.9\python.exe D:/Django-workspace/hello_world/Log/Log_Text.py
WARNING:root:warning
ERROR:root:error
CRITICAL:root:critical

把日志写入文件

basicConfig函数传入两个参数，一个是文件名，一个是Log Level

logging.basicConfig(filename="example.log",level=logging.DEBUG)
logging.debug("debug")
logging.info('info')
logging.warning("warning")
logging.error('error')
logging.critical("critical")

运行后目录下生成example.log文件。

打开后：

设的Level 是DEBUG所以，五个LEVEL的信息都打印出来了。

Refresh日志：

logging.basicConfig(filename='example.log', filemode='w', level=logging.DEBUG)

如果不设置filemode 参数，多次运行某脚本，每次运行的message会都附加在exmaple.log后。设置后，多次运行脚本，exmaple.log 都会被清除

多模块记录

当程序中有多个模块时，该怎么记录日志？

# myapp.py

importlogging

importmylib

defmain():

    logging.basicConfig(filename='myapp.log', level=logging.INFO)

    logging.info('Started')

    mylib.do_something()

    logging.info('Finished')

if __name__ =='__main__':

    main()

# mylib.py

importlogging

defdo_something():

    logging.info('Doing something')

运行myapp.py ,结果如下：

INFO:root:Started

INFO:root:Doing something

INFO:root:Finished

记录多变量：

用%s的格式，将变量作为参数，

importlogging

logging.warning('%s before you %s','Look','leap!')

结果：

WARNING:root:Look before you leap!

展示格式

为展示时间，需要在格式日志中加入‘%(asctime)s’

importlogging

logging.basicConfig(format='%(asctime)s%(message)s')

logging.warning('is when this event was logged.')

结果：

2010-12-12 11:41:42,612 is when this event was logged.

默认是ISO8601格式展示，我们可以提供datefmt 参数给basicConfig函数来改变格式

importlogging

logging.basicConfig(format='%(asctime)s%(message)s', datefmt='%m/%d/%Y %I:%M:%S %p')

logging.warning('is when this event was logged.')