Python logging

python的logging主要有四个组件：
* logger: 日志类，应用程序往往通过调用它提供的api来记录日志；
* handler: 对日志信息处理，可以将日志发送(保存)到不同的目标域中；
* filter: 对日志信息进行过滤；
* formatter:日志的格式化；

logging是线程安全的。

控制台输出

默认情况下，logging将日志打印到屏幕，日志级别为WARNING。日志级别大小关系为：CRITICAL > ERROR > WARNING > INFO > DEBUG > NOTSET。

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

import logging

logging.debug('This is debug message')
logging.info('This is info message')
logging.warning('This is warning message')

输出

WARNING:root:This is warning message

通过logging.basicConfig函数对日志的输出格式及方式做相关配置

# -*- coding: utf-8 -*-
import logging

logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s %(message)s',
                    datefmt='%a, %d %b %Y %H:%M:%S',
                    filename='test.log',
                    filemode='w')

logging.debug('This is debug message')
logging.info('This is info message')
logging.warning('This is warning message')

当前目录下test.log内容：

Tue, 07 Feb 2017 19:51:36 python-logging.py[line:10] DEBUG This is debug message
Tue, 07 Feb 2017 19:51:36 python-logging.py[line:11] INFO This is info message
Tue, 07 Feb 2017 19:51:36 python-logging.py[line:12] WARNING This is warning message

logging.basicConfig函数各参数:
- filename: 指定日志文件名
- filemode: 和file函数意义相同，指定日志文件的打开模式，’w’或’a’
- format: 指定输出的格式和内容，format可以输出很多有用信息，如上例所示:
- %(levelno)s: 打印日志级别的数值
- %(levelname)s: 打印日志级别名称
- %(pathname)s: 打印当前执行程序的路径，其实就是sys.argv[0]
- %(filename)s: 打印当前执行程序名
- %(funcName)s: 打印日志的当前函数
- %(lineno)d: 打印日志的当前行号
- %(asctime)s: 打印日志的时间
- %(thread)d: 打印线程ID
- %(threadName)s: 打印线程名称
- %(process)d: 打印进程ID
- %(message)s: 打印日志信息
- datefmt: 指定时间格式，同time.strftime()
- level: 设置日志级别，默认为logging.WARNING
- stream: 指定将日志的输出流，可以指定输出到sys.stderr,sys.stdout或者文件，默认输出到sys.stderr，当stream和filename同时指定时，stream被忽略

将日志同时输出到文件和屏幕

# -*- coding: utf-8 -*-
import logging

logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s %(message)s',
                    datefmt='%a, %d %b %Y %H:%M:%S',
                    filename='test.log',
                    filemode='w')

#################################################################################################
# 定义一个StreamHandler，将INFO级别或更高的日志信息打印到标准错误，并将其添加到当前的日志处理对象
console = logging.StreamHandler()
console.setLevel(logging.INFO)
formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
console.setFormatter(formatter)
logging.getLogger('').addHandler(console)
#################################################################################################

logging.debug('This is debug message')
logging.info('This is info message')
logging.warning('This is warning message')

当前目录下test.log内容：

Tue, 07 Feb 2017 19:56:23 python-logging.py[line:19] DEBUG This is debug message
Tue, 07 Feb 2017 19:56:23 python-logging.py[line:20] INFO This is info message
Tue, 07 Feb 2017 19:56:23 python-logging.py[line:21] WARNING This is warning message

控制台输出：

root        : INFO     This is info message
root        : WARNING  This is warning message

日志回滚

# -*- coding: utf-8 -*-
import logging
from logging.handlers import RotatingFileHandler

#################################################################################################
# 定义一个RotatingFileHandler，最多备份5个日志文件，每个日志文件最大10M
r_handler = RotatingFileHandler('test.log', maxBytes=10*1024*1024, backupCount=5)
r_handler.setLevel(logging.INFO)
formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
r_handler.setFormatter(formatter)
logging.getLogger('').addHandler(r_handler)

通过logging.config模块配置日志

#logger.conf
###############################################
[loggers]
keys=root,example01,example02

[logger_root]
level=DEBUG
handlers=hand01,hand02

[logger_example01]
handlers=hand01,hand02
qualname=example01
propagate=0

[logger_example02]
handlers=hand01,hand03
qualname=example02
propagate=0
###############################################
[handlers]
keys=hand01,hand02,hand03

[handler_hand01]
class=StreamHandler
level=INFO
formatter=form02
args=(sys.stderr,)

[handler_hand02]
class=FileHandler
level=DEBUG
formatter=form01
args=('test.log', 'a')

[handler_hand03]
class=handlers.RotatingFileHandler
level=INFO
formatter=form02
args=('test.log', 'a', 10*1024*1024, 5)
###############################################
[formatters]
keys=form01,form02

[formatter_form01]
format=%(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s %(message)s
datefmt=%a, %d %b %Y %H:%M:%S

[formatter_form02]
format=%(name)-12s: %(levelname)-8s %(message)s
datefmt=%a, %d %b %Y %H:%M:%S

将日志同时输出到文件和屏幕的例子：

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

import logging.config

logging.config.fileConfig("logger.conf")
logger = logging.getLogger("example01")

logger.debug('This is debug message')
logger.info('This is info message')
logger.warning('This is warning message')

日志回滚的例子：

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

import logging.config

logging.config.fileConfig("logger.conf")
logger = logging.getLogger("example02")

logger.debug('This is debug message')
logger.info('This is info message')
logger.warning('This is warning message')