Python Logging模块的简单使用

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]

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：
http://www.jianshu.com/p/25f70905ae9d
https://yinzo.github.io/14610807170718.html
http://python.jobbole.com/86887/

参考

https://docs.python.org/2/library/logging.html
https://docs.python.org/2/howto/logging.html#logging-basic-tutorial