Python 日志模块 logging

25 Aug 2018

1.logging基本类说明

Loggers 类，提供实际应用中的直接调用接口
Handlers 类，将日志内容送到合适的地方，如控制台，文件等
Filters 类，提供过滤比日志级别更细致的过滤，如从内容字段等.

Formatters 类，提供输出的格式.

  import logging

  # 创建一个logger
  logger = logging.getLogger('simple_example')
  logger.setLevel(logging.DEBUG) #最低的日志级别，大于此级别的都记录，下同

  # 创建一个handler，用于写入日志文件
  fh = logging.FileHandler('spam.log')
  fh.setLevel(logging.DEBUG)
	
   # 再创建一个handler，用于输出到控制台
  ch = logging.StreamHandler()
  ch.setLevel(logging.ERROR)
	
  # 定义handler的输出格式
  formatter = logging.Formatter(
      '%(asctime)s - %(name)s - %(levelname)s - %(message)s')
  ch.setFormatter(formatter)
  fh.setFormatter(formatter)
	
  # 给logger添加handler
  logger.addHandler(ch)
  logger.addHandler(fh)
	
  # 记录日志
  logger.debug('debug message')
  logger.info('info message')
  logger.warn('warn message')
  logger.error('error message')
  logger.critical('critical message')

2.日志的级别

日志的级别：

Level	Numeric value
CRITICAL	50
ERROR		40
WARNING		30
INFO		20
DEBUG		10
NOTSET		0

3.日志格式

默认是：’%(message)s’

有两种格式化方式：

{}类型，三种特殊的标志: ‘!s’ 代表求值后调用 str(), ‘!r’ 调用 repr()，’!a’ 调用ascii().

  "First, thou shalt count to {0}"  # References first positional argument
  "Bring me a {}"                   # Implicitly references the first positional argument
  "From {} to {}"                   # Same as "From {0} to {1}"
  "My quest is {name}"              # References keyword argument 'name'
  "Weight in tons {0.weight}"       # 'weight' attribute of first positional arg
  "Units destroyed: {players[0]}"   # First element of keyword argument 'players'.

  "Harold's a clever {0!s}"        # Calls str() on the argument first
  "Bring out the holy {name!r}"    # Calls repr() on the argument first
  "More {!a}"                      # Calls ascii() on the argument first

  示例：
  >>"The sum of 1 + 2 is {0}".format(1+2)
  'The sum of 1 + 2 is 3'

模板

  >>> from string import Template
  >>> s = Template('$who likes $what')
  >>> s.substitute(who='tim', what='kung pao')
  'tim likes kung pao'
  >>> d = dict(who='tim')
  >>> Template('Give $who $100').substitute(d)
  Traceback (most recent call last):
  ...
  ValueError: Invalid placeholder in string: line 1, col 11
  >>> Template('$who likes $what').substitute(d)
  Traceback (most recent call last):
  ...
  KeyError: 'what'
  >>> Template('$who likes $what').safe_substitute(d)
  'tim likes $what'

所有可用的属性字段：

参考：