前言
日志是非常重要的，最近有接触到这个，所以系统的看一下python这个模块的用法。本文即为Logging模块的用法简介，主要参考文章为Python官方文档，链接见参考列表。
另外，Python的 HOWTOs文档 很详细，连日志该怎么用都写了，所以有英文阅读能力的同学建议去阅读一下。
Logging模块构成 组成主要分为四个部分：
Loggers：提供应用程序直接使用的接口 Handlers：将Loggers产生的日志传到指定位置 Filters：对输出日志进行过滤 Formatters：控制输出格式 日志级别 Level Numeric value When it’s used DEBUG 10 Detailed information, typically of interest only when diagnosing problems. INFO 20 Confirmation that things are working as expected. WARNING 30 An 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. ERROR 40 Due to a more serious problem, the software has not been able to perform some function. CRITICAL 50 A serious error, indicating that the program itself may be unable to continue running. NOSET 0 getattr(logging, loglevel.upper())默认级别是WARNING，可以使用打印到屏幕上的方式记录，也可以记录到文件中。
模块使用示例 简单例子 打印输出 In [5]: import logging In [6]: logging.warning("FBI warning") WARNING:root:FBI warning In [7]: logging.info("information") # 没有打印是因为默认级别是warning 输出到文件中 In [4]: import logging In [5]: logging.basicConfig(filename='example.log', level=logging.DEBUG) In [6]: logging.debug("debug") In [7]: logging.warning('warning') In [8]: logging.info('info') In [9]: ls C++ STL/ a.py example.log parser/ test.sh* In [10]: cat example.log DEBUG:root:debug WARNING:root:warning INFO:root:info In [14]: logging.warning('new warning') # 注意这种是直接往后面添加，也就是add的，若是想覆盖内容可以更改文件写入方式 In [15]: cat example.log DEBUG:root:debug WARNING:root:warning INFO:root:info WARNING:root:new warning # 覆盖的方式写入例子 (test) test ipython WARNING: Attempting to work in a virtualenv. If you encounter problems, please install IPython inside the virtualenv. Python 2.7.11 (default, Jun 17 2016, 20:01:51) Type "copyright", "credits" or "license" for more information. IPython 4.2.0 -- An enhanced Interactive Python. ? -> Introduction and overview of IPython's features. %quickref -> Quick reference. help -> Python's own help system. object? -> Details about 'object', use 'object??' for extra details. In [1]: import logging In [2]: logging.basicConfig(filename='example.log', filemode='w', level=logging.DEBUG) In [3]: logging.warning('FBI warning') In [4]: ls C++ STL/ a.py example.log parser/ test.sh* In [5]: cat example.log WARNING:root:FBI warning In [6]: quit (test) test ipython WARNING: Attempting to work in a virtualenv. If you encounter problems, please install IPython inside the virtualenv. Python 2.7.11 (default, Jun 17 2016, 20:01:51) Type "copyright", "credits" or "license" for more information. IPython 4.2.0 -- An enhanced Interactive Python. ? -> Introduction and overview of IPython's features. %quickref -> Quick reference. help -> Python's own help system. object? -> Details about 'object', use 'object??' for extra details. In [1]: import logging In [2]: logging.basicConfig(filename='example.log', filemode='w', level=logging.DEBUG) In [3]: logging.warning('warning') In [4]: cat example.log WARNING:root:warning 变量的使用和 print 语句中使用变量一样，如:
In [5]: logging.warning('%s before you %s', 'Look', 'leap!') In [6]: cat example.log WARNING:root:warning WARNING:root:Look before you leap! 输出格式可以在 basicConfig 中设置，参数名称可以参见 链接 ，可以设置时间什么的，如：
In [2]: import logging In [3]: logging.basicConfig(format='%(asctime)s:%(levelname)s:%(message)s', level=logging.DEBUG) In [4]: logging.warning('And this, too') 2016-12-06 15:40:43,577:WARNING:And this, too 进阶使用当想项目中使用logging模块的时候肯定不能在这样一句句的写了，一般可能会抽象出一个模块来，这样比较有效一些。logging模块提供了四个类（Loggers，Formatters，Filtters,Handlers）来实现不同的功能，与此对应的我们如果想封装一个函数，也就要针对这几个功能来自定义一下。
想自定义的话思路也很简单，首先实例化一个相应的对象，然后进行一些设置，可以简单看一下下面的例子：
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') # 输出是： $ python simple_logging_module.py 2005-03-19 15:10:26,618 - simple_example - DEBUG - debug message 2005-03-19 15:10:26,620 - simple_example - INFO - info message 2005-03-19 15:10:26,695 - simple_example - WARNING - warn message 2005-03-19 15:10:26,697 - simple_example - ERROR - error message 2005-03-19 15:10:26,773 - simple_example - CRITICAL - critical message 从配置文件导入配置模块内容：
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') # 输出 $ python simple_logging_config.py 2005-03-19 15:38:55,977 - simpleExample - DEBUG - debug message 2005-03-19 15:38:55,979 - simpleExample - INFO - info message 2005-03-19 15:38:56,054 - simpleExample - WARNING - warn message 2005-03-19 15:38:56,055 - simpleExample - ERROR - error message 2005-03-19 15:38:56,130 - simpleExample - CRITICAL - critical message配置文件内容：
[loggers] keys=root,simpleExample [handlers] keys=consoleHandler [formatters] keys=simpleFormatter [logger_root] level=DEBUG handlers=consoleHandler [logger_simpleExample] level=DEBUG handlers=consoleHandler qualname=simpleExample propagate=0 [handler_consoleHandler] class=StreamHandler level=DEBUG formatter=simpleFormatter args=(sys.stdout,) [formatter_simpleFormatter] format=%(asctime)s - %(name)s - %(levelname)s - %(message)s同时也可以使用YAML格式的配置文件，如：
version: 1 formatters: simple: format: '%(asctime)s - %(name)s - %(levelname)s - %(message)s' handlers: console: class: logging.StreamHandler level: DEBUG formatter: simple stream: ext://sys.stdout loggers: simpleExample: level: DEBUG handlers: [console] propagate: no root: level: DEBUG handlers: [console] PSLogging模块使用也会有很多坑，常见的是日志重复打印的问题，大家可以搜一下，这里提供一些链接供参考：