Python日志打印里logging.getLogger源码分析详解


Posted in Python onJanuary 17, 2021

实践环境

WIN 10

Python 3.6.5

函数说明

logging.getLogger(name=None)

getLogger函数位于logging/__init__.py脚本

源码分析

_loggerClass = Logger
# ...略
 
root = RootLogger(WARNING)
Logger.root = root
Logger.manager = Manager(Logger.root)
 
# ...略
 
def getLogger(name=None):
  """
  Return a logger with the specified name, creating it if necessary.
 
  If no name is specified, return the root logger.
  """
  if name:
    return Logger.manager.getLogger(name)
  else:
    return root

结论:如函数注释所述,如果调用getLogger时,如果没有指定函数参数(即要获取的日志打印器名称)或者参数值不为真,则默认返回root打印器

Logger.manager.getLogger(self, name)源码分析

该函数位于logging/__init__.py脚本

class Manager(object):
  """
  There is [under normal circumstances] just one Manager instance, which
  holds the hierarchy of loggers.
  """
  def __init__(self, rootnode):
    """
    Initialize the manager with the root node of the logger hierarchy.
    """
    self.root = rootnode
    self.disable = 0
    self.emittedNoHandlerWarning = False
    self.loggerDict = {}
    self.loggerClass = None
    self.logRecordFactory = None
 
  def getLogger(self, name):
    """
    Get a logger with the specified name (channel name), creating it
    if it doesn't yet exist. This name is a dot-separated hierarchical
    name, such as "a", "a.b", "a.b.c" or similar.
 
    If a PlaceHolder existed for the specified name [i.e. the logger
    didn't exist but a child of it did], replace it with the created
    logger and fix up the parent/child references which pointed to the
    placeholder to now point to the logger.
    """
    rv = None
    if not isinstance(name, str):
      raise TypeError('A logger name must be a string')
    _acquireLock()
    try:
      if name in self.loggerDict:
        rv = self.loggerDict[name]
        if isinstance(rv, PlaceHolder):
          ph = rv
          rv = (self.loggerClass or _loggerClass)(name)
          rv.manager = self
          self.loggerDict[name] = rv
          self._fixupChildren(ph, rv)
          self._fixupParents(rv)
      else:
        rv = (self.loggerClass or _loggerClass)(name) # _loggerClass = Logger
        rv.manager = self
        self.loggerDict[name] = rv
        self._fixupParents(rv)
    finally:
      _releaseLock()
    return rv

Logger源码分析

_nameToLevel = {
  'CRITICAL': CRITICAL,
  'FATAL': FATAL,
  'ERROR': ERROR,
  'WARN': WARNING,
  'WARNING': WARNING,
  'INFO': INFO,
  'DEBUG': DEBUG,
  'NOTSET': NOTSET,
}
 
# ...略
 
def _checkLevel(level):
  if isinstance(level, int):
    rv = level
  elif str(level) == level:
    if level not in _nameToLevel:
      raise ValueError("Unknown level: %r" % level)
    rv = _nameToLevel[level]
  else:
    raise TypeError("Level not an integer or a valid string: %r" % level)
  return rv
 
# ...略
class PlaceHolder(object):
  """
  PlaceHolder instances are used in the Manager logger hierarchy to take
  the place of nodes for which no loggers have been defined. This class is
  intended for internal use only and not as part of the public API.
  """
  def __init__(self, alogger):
    """
    Initialize with the specified logger being a child of this placeholder.
    """
    self.loggerMap = { alogger : None }
 
  def append(self, alogger):
    """
    Add the specified logger as a child of this placeholder.
    """
    if alogger not in self.loggerMap:
      self.loggerMap[alogger] = None
 
 
 
class Logger(Filterer):
  """
  Instances of the Logger class represent a single logging channel. A
  "logging channel" indicates an area of an application. Exactly how an
  "area" is defined is up to the application developer. Since an
  application can have any number of areas, logging channels are identified
  by a unique string. Application areas can be nested (e.g. an area
  of "input processing" might include sub-areas "read CSV files", "read
  XLS files" and "read Gnumeric files"). To cater for this natural nesting,
  channel names are organized into a namespace hierarchy where levels are
  separated by periods, much like the Java or Python package namespace. So
  in the instance given above, channel names might be "input" for the upper
  level, and "input.csv", "input.xls" and "input.gnu" for the sub-levels.
  There is no arbitrary limit to the depth of nesting.
  """
  def __init__(self, name, level=NOTSET):
    """
    Initialize the logger with a name and an optional level.
    """
    Filterer.__init__(self)
    self.name = name
    self.level = _checkLevel(level)
    self.parent = None
    self.propagate = True
    self.handlers = []
    self.disabled = False
 
  # ... 略

结论:如果调用logging.getLogger()时,有指定日志打印器名称,且名称为真(不为空字符串,0,False等False值),

1)如果名称为不存在的日志打印器名称,则,且参数值为真,但是即要获取的日志打印器名称)或者参数值不为真,则创建一个名为给定参数值的日志打印器,该日志打印器,默认级别默认为NOTSET,disable_existing_loggers配置为False,propagate配置为True。然后在日志打印器字典中记录该名称和日志打印器的映射关系,接着调用 _fixupParents(创建的日志打印器实例)类实例方法--为日志打印器设置上级日志打印器,最后返回该日志打印器。

2)如果名称已存在日志打印器名称,则获取该日志打印器,然后判断日志打印器是否为PlaceHolder类实例,如果是,则创建一个名为所给参数值的日志打印器,同第1)点,该日志打印器,默认级别默认为NOTSET,disable_existing_loggers配置为False,propagate配置为True。然后在日志打印器字典中记录该名称和日志打印器的映射关系,接着调用 _fixupParents(创建的打印器实例)类实例方法,_fixupChildren(PlaceHolder类实例--根据名称获取的日志打印器,新建的日志打印器实例)--为新建日志打印器设置上级日志打印器,为PlaceHolder类实例现有下级PlaceHolder日志打印器实例重新设置上级日志打印器,最后返回该日志打印器。

_fixupParents及_fixupChildren函数源码分析

# _fixupParents
 
# ...略
class Manager(object):
  # ...略
  def _fixupParents(self, alogger):
    """
    Ensure that there are either loggers or placeholders all the way
    from the specified logger to the root of the logger hierarchy.
    """
    name = alogger.name # 获取日志打印器名称
    i = name.rfind(".")
    rv = None # 存放alogger日志打印器的上级日志打印器
    while (i > 0) and not rv: # 如果名称中存在英文的点,并且找到上级日志打印器
      substr = name[:i] # 获取名称中位于最后一个英文的点的左侧字符串(暂且称至为 点分上级)
      if substr not in self.loggerDict: # 如果 点分上级 不存在日志打印器字典中
        self.loggerDict[substr] = PlaceHolder(alogger) # 创建PlaceHolder实例作为 点分上级 对应的日志打印器 # 继续查找点分上级日志打印器 # 注意,这里的PlaceHolder仅是占位用,不是真的打印器,这里为了方便描述,暂且称之为PlaceHolder日志打印器
      else: # 否则
        obj = self.loggerDict[substr] # 获取 点分上级 对应的日志打印器
        if isinstance(obj, Logger): # 如果为Logger实例,如果是,则跳出循环,执行 # 为日志打印器设置上级
          rv = obj
        else: # 否则
          assert isinstance(obj, PlaceHolder) # 断言它为PlaceHolder的实例
          obj.append(alogger) # 把日志打印器添加为点分上级对应的PlaceHolder日志打印器实例的下级日志打印器 执行 # 继续查找点分上级日志打印器
      i = name.rfind(".", 0, i - 1) # 继续查找点分上级日志打印器
    if not rv: # 找不到点分上级、或者遍历完所有点分上级,都没找到上级日志打印器
      rv = self.root # 则 把root日志打印器设置为alogger日志打印器的上级日志打印器
    alogger.parent = rv # 为日志打印器设置上级
 
 
 
  def _fixupChildren(self, ph, alogger):
    """
    Ensure that children of the placeholder ph are connected to the
    specified logger.
    """
    name = alogger.name # 获取日志打印器名称
    namelen = len(name) # 获取日志打印器名称长度
    for c in ph.loggerMap.keys(): # 遍历获取的PlaceHolder日志打印器实例的子级日志打印器
      #The if means ... if not c.parent.name.startswith(nm)
      if c.parent.name[:namelen] != name: # 如果PlaceHolder日志打印器实例名称不以alogger日志打印器名称为前缀,
        alogger.parent = c.parent # 那么,设置alogger日志打印器的上级日志打印器为PlaceHolder日志打印器
        c.parent = alogger # 设置alogger日志打印器为PlaceHolder日志打印器原有下级PlaceHolder日志打印器的上级

结论:日志打印器都是分父子级的,这个父子层级是怎么形成的,参见上述函数代码注解

到此这篇关于Python日志打印里logging.getLogger源码分析详解的文章就介绍到这了,更多相关Python logging.getLogger源码分析内容请搜索三水点靠木以前的文章或继续浏览下面的相关文章希望大家以后多多支持三水点靠木!

Python 相关文章推荐
Pyhton中防止SQL注入的方法
Feb 05 Python
python3实现暴力穷举博客园密码
Jun 19 Python
Python执行时间的计算方法小结
Mar 17 Python
Python常用时间操作总结【取得当前时间、时间函数、应用等】
May 11 Python
Python实现的栈(Stack)
Jan 26 Python
设置python3为默认python的方法
Oct 31 Python
在Pycharm terminal中字体大小设置的方法
Jan 16 Python
在Django下测试与调试REST API的方法详解
Aug 29 Python
Django自带日志 settings.py文件配置方法
Aug 30 Python
python实现统计代码行数的小工具
Sep 19 Python
python itsdangerous模块的具体使用方法
Feb 17 Python
Python如何将字符串转换为日期
Jul 31 Python
Python中的面向接口编程示例详解
Jan 17 #Python
Python学习之time模块的基本使用
Jan 17 #Python
python中re模块知识点总结
Jan 17 #Python
史上最详细的Python打包成exe文件教程
Jan 17 #Python
python制作微博图片爬取工具
Jan 16 #Python
python工具——Mimesis的简单使用教程
Jan 16 #Python
Python 内存管理机制全面分析
Jan 16 #Python
You might like
中国广播史趣谈 — 几个历史第一次
2021/03/01 无线电
PHP单例模式详细介绍
2015/07/01 PHP
无需数据库在线投票调查php代码
2016/07/20 PHP
phpmailer绑定邮箱的实现方法
2016/12/01 PHP
IE和FireFox(FF)中js和css的不同
2009/04/13 Javascript
JS 树形递归实例代码
2010/05/18 Javascript
jQuery Validate验证框架经典大全
2015/09/23 Javascript
jQuery实现的网页左侧在线客服效果代码
2015/10/23 Javascript
JS 拼凑字符串的简单实例
2016/09/02 Javascript
巧用数组制作图片切换js代码
2016/11/29 Javascript
学习vue.js表单控件绑定操作
2016/12/05 Javascript
Bootstrap模态框插入视频的实现代码
2017/06/25 Javascript
Angular2关于@angular/cli默认端口号配置的问题
2017/07/15 Javascript
vue.js中$set与数组更新方法
2018/03/08 Javascript
webpack 静态资源集中输出的方法示例
2018/11/09 Javascript
Vue项目history模式下微信分享爬坑总结
2019/03/29 Javascript
详解ES6 Promise的生命周期和创建
2019/08/18 Javascript
es6 super关键字的理解与应用实例分析
2020/02/15 Javascript
Python 调用VC++的动态链接库(DLL)
2008/09/06 Python
Python中asyncore异步模块的用法及实现httpclient的实例
2016/06/28 Python
python中virtualenvwrapper安装与使用
2018/05/20 Python
pyshp创建shp点文件的方法
2018/12/31 Python
pyqt 实现QlineEdit 输入密码显示成圆点的方法
2019/06/24 Python
python编写计算器功能
2019/10/25 Python
Win10下配置tensorflow-gpu的详细教程(无VS2015/2017)
2020/07/14 Python
python 实现倒计时功能(gui界面)
2020/11/11 Python
利达恒信公司.NET笔试题面试题
2016/03/05 面试题
岗位职责定义及内容
2013/11/08 职场文书
微信营销策划方案
2014/02/24 职场文书
机械制造专业毕业生求职信
2014/03/02 职场文书
前台文员职责范本
2014/03/07 职场文书
初中班主任经验交流材料
2014/05/16 职场文书
人力资源管理系自荐信
2014/05/31 职场文书
食品安全汇报材料
2014/08/18 职场文书
群众路线个人剖析材料
2014/10/07 职场文书
老人节标语大全
2014/10/08 职场文书