Python Logging模块的简单使用

布满荆棘的人生 2022-06-01 13:19 214阅读 0赞

### 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][HOWTOs]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 ####

<table style="margin-right:0px; margin-bottom:0px; margin-left:0px; padding:0px; border-color:#C0C0C0; color:rgb(0,0,0); font-family:'Helvetica Neue',Helvetica,Verdana,Arial,sans-serif; font-size:14px"> 
 <thead style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <th style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> Level</th> 
   <th style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> Numeric value</th> 
   <th style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> When it’s used</th> 
  </tr> 
 </thead> 
 <tbody style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> DEBUG</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> 10</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> Detailed information, typically of interest only when diagnosing problems.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> INFO</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> 20</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> Confirmation that things are working as expected.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> WARNING</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> 30</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> 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.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> ERROR</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> 40</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> Due to a more serious problem, the software has not been able to perform some function.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> CRITICAL</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> 50</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> A serious error, indicating that the program itself may be unable to continue running.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> NOSET</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> 0</td> 
   <td style="margin:0px; padding:3px; border-color:#C0C0C0; border-collapse:collapse"> getattr(logging, loglevel.upper())</td> 
  </tr> 
 </tbody> 
</table>

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][Link 1]，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]

### PS ###

Logging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：

1.  [http://www.jianshu.com/p/25f70905ae9d][http_www.jianshu.com_p_25f70905ae9d]
2.  [https://yinzo.github.io/14610807170718.html][https_yinzo.github.io_14610807170718.html]
3.  [http://python.jobbole.com/86887/][http_python.jobbole.com_86887]

### 参考 ###

1.  [https://docs.python.org/2/library/logging.html][https_docs.python.org_2_library_logging.html]
2.  [https://docs.python.org/2/howto/logging.html\#logging-basic-tutorial][HOWTOs]

[HOWTOs]: https://docs.python.org/2/howto/logging.html#logging-basic-tutorial
[Link 1]: https://docs.python.org/2/library/logging.html#logrecord-attributes
[http_www.jianshu.com_p_25f70905ae9d]: http://www.jianshu.com/p/25f70905ae9d
[https_yinzo.github.io_14610807170718.html]: https://yinzo.github.io/14610807170718.html
[http_python.jobbole.com_86887]: http://python.jobbole.com/86887/
[https_docs.python.org_2_library_logging.html]: https://docs.python.org/2/library/logging.html