Python标准库 - logging

编写代码时, 常要跟踪下其运行过程, 记录日志是常用的方式. 较简单的就是print命令打印到终端, 或通过open函数写入文件. 但随着代码量的增加, 该方式不可控的弊端, 也凸显出来, 这也正是logging模块出现的背景.

对于logging模块, 简单来说直接import进来, 就可以用了.

In [1]: import logging

In [2]: logging.warning('Watch out!')

WARNING:root:Watch out!

In [3]: logging.info('I told you so')

In [4]:

In [4]:

第二个语句没有输出呢, 这需了解下日志等级的概念. logging模块默认的日志等级是WARNING, 大于该等级的日志才会输出, 细节如下.

借助basicConfig方法, 可对日志记录做些配置.

In [1]: import logging

In [2]: logging.basicConfig(filename='/tmp/example.log',level=logging.DEBUG)

In [3]: logging.debug('This message should go to the log file')

In [4]: logging.info('So should this')

In [5]: logging.warning('And this, too')

$ cat /tmp/example.log

DEBUG:root:This message should go to the log file

INFO:root:So should this

WARNING:root:And this, too

在脚本中, 可按照下面的方式使用logging模块.

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# myapp.py

import logging

import mylib

def main():

    logging.basicConfig(filename='myapp.log', format='%(asctime)s - %(name)s - %(levelname)s - %(pathname)s - %(message)s', level=logging.INFO)

    logging.info('Started')

    mylib.do_something()

    logging.info('Finished')

if __name__ == '__main__':

    main()

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# mylib.py

import logging

def do_something():

    logging.info('Doing something')

$ python myapp.py

$ cat myapp.log

2018-01-19 17:00:14,821 - root - INFO - myapp.py - Started

2018-01-19 17:00:14,821 - root - INFO - /home/zz/stage/mylib.py - Doing something

2018-01-19 17:00:14,821 - root - INFO - myapp.py - Finished

简单了解了logging模块的使用, 接着看下其中几个重要的概念.

1. Logger 日志记录器, 暴露给应用程序直接使用的接口, 几个方法用于设置记录器.

Logger.setLevel() - 指定日志记录器处理的日志最低级别.

Logger.addHandler(), Logger.removeHandler() - 为日志记录器添加, 或移除处理器.

2. Handler 处理器, 将记录器获取的日志, 传送到其定义的目的地, 也有几个方法设置处理器.

setLevel() - 指定处理器处理的日志最低级别.

setFormatter() - 为处理器选择一个格式化器.

3. Formatter 格式化器, 指定日志的输出格式.

最开始说了logging模块的简单用法, 以及了解了上面的概念后, 看下开发较大应用时, 如何使用logging呢.

这主要介绍两种方式, 其一是, 将logging模块的配置直接写在应用代码中, 如下所示.

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# simple_logging_module.py

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')

$ python simple_logging_module.py

2018-01-19 21:41:58,180 - simple_example - DEBUG - debug message

2018-01-19 21:41:58,180 - simple_example - INFO - info message

2018-01-19 21:41:58,180 - simple_example - WARNING - warn message

2018-01-19 21:41:58,180 - simple_example - ERROR - error message

2018-01-19 21:41:58,180 - simple_example - CRITICAL - critical message

其二, 配置信息写入文件中, 借助fileConfig方法加载该文件, 如下所示.

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# simple_logging_config.py

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')

# logging.conf

[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

datefmt=

$ python simple_logging_config.py

2018-01-19 21:53:46,216 - simpleExample - DEBUG - debug message

2018-01-19 21:53:46,216 - simpleExample - INFO - info message

2018-01-19 21:53:46,216 - simpleExample - WARNING - warn message

2018-01-19 21:53:46,216 - simpleExample - ERROR - error message

2018-01-19 21:53:46,216 - simpleExample - CRITICAL - critical message

最后简单说下, 如何总结一个模块, 可围绕下面三点进行说明.

1. 该模块解决的问题, 其它方法是如何做的.

2. 模块的使用, 以及核心概念(或定义).

3. 核心API的梳理.