Python logging实用指南

1. 简单的将日志打印到屏幕

Python内置的logging模块提供了强大的日志功能，默认情况下日志级别为WARNING，日志级别大小关系为：CRITICAL > ERROR > WARNING > INFO > DEBUG > NOTSET。以下示例展示了如何将日志信息打印到屏幕：

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

屏幕上打印结果：

WARNING:root:This is warning message

2. 通过`logging.basicConfig`函数对日志进行格式化和配置

可以通过logging.basicConfig函数对日志的输出格式和方式进行配置，例如指定日志文件名、输出格式、时间格式等：

import logginglogging.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='myapp.log',    filemode='w')logging.debug('This is debug message')logging.info('This is info message')logging.warning('This is warning message')

myapp.log文件内容示例：

Sun, 24 May 2009 21:48:54 demo2.py[line:11] DEBUG This is debug messageSun, 24 May 2009 21:48:54 demo2.py[line:12] INFO This is info messageSun, 24 May 2009 21:48:54 demo2.py[line:13] WARNING This is warning message

logging.basicConfig函数参数说明：

filename：指定日志文件名

filemode：指定日志文件的打开模式，支持w或a

format：指定日志输出格式

datefmt：指定日期时间格式

level：设置日志级别，默认为WARNING

stream：指定日志输出流，默认为sys.stderr

3. 将日志同时输出到文件和屏幕

可以通过定义多个日志处理器，将日志信息同时输出到文件和屏幕：

import logging# 定义一个StreamHandler，将INFO级别或更高的日志信息打印到标准错误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')

屏幕上打印结果：

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

myapp.log文件内容示例：

Sun, 24 May 2009 21:48:54 demo2.py[line:11] DEBUG This is debug messageSun, 24 May 2009 21:48:54 demo2.py[line:12] INFO This is info messageSun, 24 May 2009 21:48:54 demo2.py[line:13] WARNING This is warning message

4. 日志回滚

可以使用RotatingFileHandler对日志进行回滚，设置日志文件最大大小和备份文件数量：

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10MBrthandler = RotatingFileHandler('myapp.log', maxBytes=10*1024*1024, backupCount=5)rthandler.setLevel(logging.INFO)formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')rthandler.setFormatter(formatter)logging.getLogger('').addHandler(rthandler)

5. 使用`logging.config`模块进行日志配置

可以通过配置文件来管理日志设置，例如logger.conf：

[loggers]keys = root, example01, example02[logger_root]level = DEBUGhandlers = hand01, hand02[logger_example01]handlers = hand01, hand02qualname = example01propagate = 0[logger_example02]handlers = hand01, hand03qualname = example02propagate = 0[handlers]keys = hand01, hand02, hand03[handler_hand01]class = StreamHandlerlevel = INFOformatter = form02args = (sys.stderr,)[handler_hand02]class = FileHandlerlevel = DEBUGformatter = form01args = ('myapp.log', 'a')[handler_hand03]class = RotatingFileHandlerlevel = INFOformatter = form02args = ('myapp.log', 'a', 10*1024*1024, 5)[formatters]keys = form01, form02[formatter_form01]format = %(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s %(message)sdatefmt = %a, %d %b %Y %H:%M:%S[formatter_form02]format = %(name)-12s: %(levelname)-8s %(message)sdatefmt =

使用示例：

import loggingimport logging.configlogging.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')

6. logging是线程安全的

logging模块设计为线程安全，适用于多线程环境。

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