爱站程序员基地日志打印之logging.getLogger源码分析
By:授客 QQ：1033553122
#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 = rootLogger.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, whichholds the hierarchy of loggers.\"\"\"def __init__(self, rootnode):\"\"\"Initialize the manager with the root node of the logger hierarchy.\"\"\"self.root = rootnodeself.disable = 0self.emittedNoHandlerWarning = Falseself.loggerDict = {}self.loggerClass = Noneself.logRecordFactory = Nonedef getLogger(self, name):\"\"\"Get a logger with the specified name (channel name), creating itif it doesn\'t yet exist. This name is a dot-separated hierarchicalname, such as \"a\", \"a.b\", \"a.b.c\" or similar.If a PlaceHolder existed for the specified name [i.e. the loggerdidn\'t exist but a child of it did], replace it with the createdlogger and fix up the parent/child references which pointed to theplaceholder to now point to the logger.\"\"\"rv = Noneif 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 = rvrv = (self.loggerClass or _loggerClass)(name)rv.manager = selfself.loggerDict[name] = rvself._fixupChildren(ph, rv)self._fixupParents(rv)else:rv = (self.loggerClass or _loggerClass)(name) # _loggerClass = Loggerrv.manager = selfself.loggerDict[name] = rvself._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 = levelelif 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 takethe place of nodes for which no loggers have been defined. This class isintended 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] = Noneclass 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 anapplication can have any number of areas, logging channels are identifiedby a unique string. Application areas can be nested (e.g. an areaof \"input processing\" might include sub-areas \"read CSV files\", \"readXLS files\" and \"read Gnumeric files\"). To cater for this natural nesting,channel names are organized into a namespace hierarchy where levels areseparated by periods, much like the Java or Python package namespace. Soin the instance given above, channel names might be \"input\" for the upperlevel, 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 = nameself.level = _checkLevel(level)self.parent = Noneself.propagate = Trueself.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 wayfrom 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 = objelse: # 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 thespecified 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
