Python日志输出——logging模块（转）
1. logging介绍Python的logging模块提供了通用的日志系统，可以方便第三方模块或者是应用使用。这个模块提供不同的日志级别，并可以采用不同的方式记录日志，比如文件，HTTP GET/POST，SMTP，Socket等，甚至可以自己实现具体的日志记录方式。
logging模块与log4j的机制是一样的，只是具体的实现细节不同。模块提供logger，handler，filter，formatter。
logger：提供日志接口，供应用代码使用。logger最长用的操作有两类：配置和发送日志消息。可以通过logging.getLogger(name)获取logger对象，如果不指定name则返回root对象，多次使用相同的name调用getLogger方法返回同一个logger对象。
handler：将日志记录（log record）发送到合适的目的地（destination），比如文件，socket等。一个logger对象可以通过addHandler方法添加0到多个handler，每个handler又可以定义不同日志级别，以实现日志分级过滤显示。
filter：提供一种优雅的方式决定一个日志记录是否发送到handler。
formatter：指定日志记录输出的具体格式。formatter的构造方法需要两个参数：消息的格式字符串和日期字符串，这两个参数都是可选的。
与log4j类似，logger，handler和日志消息的调用可以有具体的日志级别（Level），只有在日志消息的级别大于logger和handler的级别。
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[*]import logging
[*]import logging.handlers
[*]
[*]LOG_FILE = 'tst.log'
[*]
[*]handler = logging.handlers.RotatingFileHandler(LOG_FILE, maxBytes = 1024*1024, backupCounts = 5) # 实例化handler
[*]fmt = '%(asctime)s - %(filename)s:%(lineno)s - %(name)s - %(message)s'
[*]
[*]formatter = logging.Formatter(fmt) # 实例化formatter
[*]handler.setFormatter(formatter) # 为handler添加formatter
[*]
[*]logger = logging.getLogger('tst') # 获取名为tst的logger
[*]logger.addHandler(handler) # 为logger添加handler
[*]logger.setLevel(logging.DEBUG)
[*]
[*]logger.info('first info message')
[*]logger.debug('first debug message')
import logging
import logging.handlers
LOG_FILE = 'tst.log'
handler = logging.handlers.RotatingFileHandler(LOG_FILE, maxBytes = 1024*1024, backupCounts = 5) # 实例化handler
fmt = '%(asctime)s - %(filename)s:%(lineno)s - %(name)s - %(message)s'
formatter = logging.Formatter(fmt) # 实例化formatter
handler.setFormatter(formatter) # 为handler添加formatter
logger = logging.getLogger('tst') # 获取名为tst的logger
logger.addHandler(handler) # 为logger添加handler
logger.setLevel(logging.DEBUG)
logger.info('first info message')
logger.debug('first debug message')
输出：
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[*]2012-03-04 23:21:59,682 - log_test.py:16 - tst - first info message
[*]2012-03-04 23:21:59,682 - log_test.py:17 - tst - first debug message
2012-03-04 23:21:59,682 - log_test.py:16 - tst - first info message
2012-03-04 23:21:59,682 - log_test.py:17 - tst - first debug message
关于formatter的配置，采用的是%()s的形式，就是字典的关键字替换。提供的关键字包括：
FormatDescription
%(name)s
Name of the logger (logging channel).
%(levelno)s
Numeric logging level for the message (DEBUG, INFO, WARNING, ERROR, CRITICAL).
%(levelname)s
Text logging level for the message ('DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL').
%(pathname)s
Full pathname of the source file where the logging call was issued (if available).
%(filename)s
Filename portion of pathname.
%(module)s
Module (name portion of filename).
%(funcName)s
Name of function containing the logging call.
%(lineno)d
Source line number where the logging call was issued (if available).
%(created)f
Time when the LogRecord was created (as returned by time.time()).
%(relativeCreated)d
Time in milliseconds when the LogRecord was created, relative to the time the logging module was loaded.
%(asctime)s
Human-readable time when the LogRecord was created. By default this is of the form “2003-07-08 16:49:45,896” (the numbers after the comma are millisecond portion of the time).
%(msecs)d
Millisecond portion of the time when the LogRecord was created.
%(thread)d
Thread ID (if available).
%(threadName)s
Thread name (if available).
%(process)d
Process ID (if available).
%(message)s
The logged message, computed as msg % args.
这个是摘自官网，提供了很多信息。
2. logging的配置
logging的配置可以采用python代码或是配置文件。python代码的方式就是在应用的主模块中，构建handler，handler，formatter等对象。而配置文件的方式是将这些对象的依赖关系分离出来放在文件中。比如前面的例子就类似于python代码的配置方式。这里看一下采用配置文件的方式。
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[*]import logging
[*]import logging.config
[*]
[*]logging.config.fileConfig("logging.conf") # 采用配置文件
[*]
[*]# 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")
import logging
import logging.config
logging.config.fileConfig("logging.conf") # 采用配置文件
# 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")
loggin.conf采用了模式匹配的方式进行配置，正则表达式是r'^[(.*)]$'，从而匹配出所有的组件。对于同一个组件具有多个实例的情况使用逗号‘，’进行分隔。对于一个实例的配置采用componentName_instanceName配置块。使用这种方式还是蛮简单的。
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[*]
[*]keys=root,simpleExample
[*]
[*]
[*]keys=consoleHandler
[*]
[*]
[*]keys=simpleFormatter
[*]
[*]
[*]level=DEBUG
[*]handlers=consoleHandler
[*]
[*]
[*]level=DEBUG
[*]handlers=consoleHandler
[*]qualname=simpleExample
[*]propagate=0
[*]
[*]
[*]class=StreamHandler
[*]level=DEBUG
[*]formatter=simpleFormatter
[*]args=(sys.stdout,)
[*]
[*]
[*]format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
[*]datefmt=
keys=root,simpleExample
keys=consoleHandler
keys=simpleFormatter
level=DEBUG
handlers=consoleHandler
level=DEBUG
handlers=consoleHandler
qualname=simpleExample
propagate=0
class=StreamHandler
level=DEBUG
formatter=simpleFormatter
args=(sys.stdout,)
format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
datefmt=
在指定handler的配置时，class是具体的handler类的类名，可以是相对logging模块或是全路径类名，比如需要RotatingFileHandler，则class的值可以为：RotatingFileHandler或者logging.handlers.RotatingFileHandler。args就是要传给这个类的构造方法的参数，就是一个元组，按照构造方法声明的参数的顺序。
输出：
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[*]2012-03-06 00:09:35,713 - simpleExample - DEBUG - debug message
[*]2012-03-06 00:09:35,713 - simpleExample - INFO - info message
[*]2012-03-06 00:09:35,714 - simpleExample - WARNING - warn message
[*]2012-03-06 00:09:35,714 - simpleExample - ERROR - error message
[*]2012-03-06 00:09:35,714 - simpleExample - CRITICAL - critical message
2012-03-06 00:09:35,713 - simpleExample - DEBUG - debug message
2012-03-06 00:09:35,713 - simpleExample - INFO - info message
2012-03-06 00:09:35,714 - simpleExample - WARNING - warn message
2012-03-06 00:09:35,714 - simpleExample - ERROR - error message
2012-03-06 00:09:35,714 - simpleExample - CRITICAL - critical message
这里还要明确一点，logger对象是有继承关系的，比如名为a.b和a.c的logger都是名为a的子logger，并且所有的logger对象都继承于root。如果子对象没有添加handler等一些配置，会从父对象那继承。这样就可以通过这种继承关系来复用配置。
3. 多模块使用logging
logging模块保证在同一个python解释器内，多次调用logging.getLogger('log_name')都会返回同一个logger实例，即使是在多个模块的情况下。所以典型的多模块场景下使用logging的方式是在main模块中配置logging，这个配置会作用于多个的子模块，然后在其他模块中直接通过getLogger获取Logger对象即可。 这里使用上面配置文件：
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[*]
[*]keys=root,main
[*]
[*]
[*]keys=consoleHandler,fileHandler
[*]
[*]
[*]keys=fmt
[*]
[*]
[*]level=DEBUG
[*]handlers=consoleHandler
[*]
[*]
[*]level=DEBUG
[*]qualname=main
[*]handlers=fileHandler
[*]
[*]
[*]class=StreamHandler
[*]level=DEBUG
[*]formatter=fmt
[*]args=(sys.stdout,)
[*]
[*]
[*]class=logging.handlers.RotatingFileHandler
[*]level=DEBUG
[*]formatter=fmt
[*]args=('tst.log','a',20000,5,)
[*]
[*]
[*]format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
[*]datefmt=
keys=root,main
keys=consoleHandler,fileHandler
keys=fmt
level=DEBUG
handlers=consoleHandler
level=DEBUG
qualname=main
handlers=fileHandler
class=StreamHandler
level=DEBUG
formatter=fmt
args=(sys.stdout,)
class=logging.handlers.RotatingFileHandler
level=DEBUG
formatter=fmt
args=('tst.log','a',20000,5,)
format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
datefmt=
主模块main.py：
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[*]import logging
[*]import logging.config
[*]
[*]logging.config.fileConfig('logging.conf')
[*]root_logger = logging.getLogger('root')
[*]root_logger.debug('test root logger...')
[*]
[*]logger = logging.getLogger('main')
[*]logger.info('test main logger')
[*]logger.info('start import module \'mod\'...')
[*]import mod
[*]
[*]logger.debug('let\'s test mod.testLogger()')
[*]mod.testLogger()
[*]
[*]root_logger.info('finish test...')
import logging
import logging.config
logging.config.fileConfig('logging.conf')
root_logger = logging.getLogger('root')
root_logger.debug('test root logger...')
logger = logging.getLogger('main')
logger.info('test main logger')
logger.info('start import module \'mod\'...')
import mod
logger.debug('let\'s test mod.testLogger()')
mod.testLogger()
root_logger.info('finish test...')
子模块mod.py：
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[*]import logging
[*]import submod
[*]
[*]logger = logging.getLogger('main.mod')
[*]logger.info('logger of mod say something...')
[*]
[*]def testLogger():
[*] logger.debug('this is mod.testLogger...')
[*] submod.tst()
import logging
import submod
logger = logging.getLogger('main.mod')
logger.info('logger of mod say something...')
def testLogger():
logger.debug('this is mod.testLogger...')
submod.tst()
子子模块submod.py：
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[*]import logging
[*]
[*]logger = logging.getLogger('main.mod.submod')
[*]logger.info('logger of submod say something...')
[*]
[*]def tst():
[*] logger.info('this is submod.tst()...')
import logging
logger = logging.getLogger('main.mod.submod')
logger.info('logger of submod say something...')
def tst():
logger.info('this is submod.tst()...')
然后运行python main.py，控制台输出：
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[*]2012-03-09 18:22:22,793 - root - DEBUG - test root logger...
[*]2012-03-09 18:22:22,793 - main - INFO - test main logger
[*]2012-03-09 18:22:22,809 - main - INFO - start import module 'mod'...
[*]2012-03-09 18:22:22,809 - main.mod.submod - INFO - logger of submod say something...
[*]2012-03-09 18:22:22,809 - main.mod - INFO - logger say something...
[*]2012-03-09 18:22:22,809 - main - DEBUG - let's test mod.testLogger()
[*]2012-03-09 18:22:22,825 - main.mod - DEBUG - this is mod.testLogger...
[*]2012-03-09 18:22:22,825 - main.mod.submod - INFO - this is submod.tst()...
[*]2012-03-09 18:22:22,841 - root - INFO - finish test...
2012-03-09 18:22:22,793 - root - DEBUG - test root logger...
2012-03-09 18:22:22,793 - main - INFO - test main logger
2012-03-09 18:22:22,809 - main - INFO - start import module 'mod'...
2012-03-09 18:22:22,809 - main.mod.submod - INFO - logger of submod say something...
2012-03-09 18:22:22,809 - main.mod - INFO - logger say something...
2012-03-09 18:22:22,809 - main - DEBUG - let's test mod.testLogger()
2012-03-09 18:22:22,825 - main.mod - DEBUG - this is mod.testLogger...
2012-03-09 18:22:22,825 - main.mod.submod - INFO - this is submod.tst()...
2012-03-09 18:22:22,841 - root - INFO - finish test...
可以看出，和预想的一样，然后在看一下tst.log，logger配置中的输出的目的地：
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[*]2012-03-09 18:22:22,793 - main - INFO - test main logger
[*]2012-03-09 18:22:22,809 - main - INFO - start import module 'mod'...
[*]2012-03-09 18:22:22,809 - main.mod.submod - INFO - logger of submod say something...
[*]2012-03-09 18:22:22,809 - main.mod - INFO - logger say something...
[*]2012-03-09 18:22:22,809 - main - DEBUG - let's test mod.testLogger()
[*]2012-03-09 18:22:22,825 - main.mod - DEBUG - this is mod.testLogger...
[*]2012-03-09 18:22:22,825 - main.mod.submod - INFO - this is submod.tst()...
2012-03-09 18:22:22,793 - main - INFO - test main logger
2012-03-09 18:22:22,809 - main - INFO - start import module 'mod'...
2012-03-09 18:22:22,809 - main.mod.submod - INFO - logger of submod say something...
2012-03-09 18:22:22,809 - main.mod - INFO - logger say something...
2012-03-09 18:22:22,809 - main - DEBUG - let's test mod.testLogger()
2012-03-09 18:22:22,825 - main.mod - DEBUG - this is mod.testLogger...
2012-03-09 18:22:22,825 - main.mod.submod - INFO - this is submod.tst()...
tst.log中没有root logger输出的信息，因为logging.conf中配置了只有main logger及其子logger使用RotatingFileHandler，而root logger是输出到标准输出。
转：http://blog.iyunv.com/chosen0ne/article/details/7319306
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