Python自带日志处理模块logging
默认的日志级别有DEBUG,INFO,WARNING,ERROR,CRITICAL，对应的函数是debug(),info(),warning(),error()和critical()

In [490]: import logging
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In [491]: LOG_FILENAME='/tmp/example.log'
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In [492]: logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG)
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In [493]: logging.debug('This message should go to the log file')

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查看/tmp/example.log的内容
$ cat /tmp/example.log?
DEBUG:root:This message should go to the log file

不断执行

logging.debug('This message should go to the log file')

/tmp/example.log会不断地刷新

日志轮转
In [639]: import glob
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In [640]: import logging
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In [641]: import logging.handlers
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In [642]: LOG_FILENAME='/tmp/logging_rotatingfile_example.out'
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In [643]: my_logger=logging.getLogger('MyLogger')
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In [644]: my_logger.setLevel(logging.DEBUG)
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In [645]: handler=logging.handlers.RotatingFileHandler(LOG_FILENAME,maxBytes=20,backupCount=5)
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In [646]: my_logger.addHandler(handler)
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In [648]: for i in range(20):
? ? my_logger.debug('i=%d' % i)
? .....:? ? ?
? .....:? ? ?
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In [650]: logfiles=glob.glob('%s*' %LOG_FILENAME)
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In [651]: for filename in logfiles:
? .....:? ? print filename
? .....:? ? ?
? .....:? ? ?
/tmp/logging_rotatingfile_example.out.1
/tmp/logging_rotatingfile_example.out.2
/tmp/logging_rotatingfile_example.out.5
/tmp/logging_rotatingfile_example.out.3
/tmp/logging_rotatingfile_example.out.4
/tmp/logging_rotatingfile_example.out

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最近的日志文件总是名为logging_rotatingfile_example.out，一旦大小达到maxBytes设置的20字节，就将轮转。

logging模块最重要的一个功能就是可以根据设置的不同的日志级别输出不同的日志信息。
import logging
import sys
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LEVELS={'debug':logging.DEBUG,
? ? ? ? 'info' :logging.INFO,
? ? ? ? 'warning':logging.WARNING,
? ? ? ? 'error':logging.ERROR,
? ? ? ? 'critical':logging.CRITICAL
? ? ? ? }
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if sys.argv > 1:
? level_name = sys.argv[1]
? level=LEVELS.get(level_name,logging.NOTSET)
? logging.basicConfig(level=level)
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logging.debug('This is a debug message')
logging.info('This is a info message')
logging.warning('This is a warning message')
logging.error('This is a error message')
logging.critical('This is a critical error message')
~? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
~

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$ python logging_level_example.py debug
DEBUG:root:This is a debug message
INFO:root:This is a info message
WARNING:root:This is a warning message
ERROR:root:This is a error message
CRITICAL:root:This is a critical error message
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$ python logging_level_example.py info
INFO:root:This is a info message
WARNING:root:This is a warning message
ERROR:root:This is a error message
CRITICAL:root:This is a critical error message
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$ python logging_level_example.py warning
WARNING:root:This is a warning message
ERROR:root:This is a error message
CRITICAL:root:This is a critical error message
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$ python logging_level_example.py error
ERROR:root:This is a error message
CRITICAL:root:This is a critical error message
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$ python logging_level_example.py critical
CRITICAL:root:This is a critical error message

logging模块包括logger，handler，filter和formatter。
Logger.setLevel()设置日志级别

Logger.addFilter()

Logger.removeFilter()

Logger.debug()

Logger.info()

Logger.warning()

Logger.error()

Logger.critical()

Logger.exception()?

Logger.log()

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