Python 的根记录器的名称是什么？

Question

我正在学习有关登录 Python 的基本教程https://docs.python.org/3/howto/logging.html#a-simple-example，并按照 iPython 控制台中的步骤进行操作。如那里所述，根记录器的默认级别是WARNING：

In [1]: import logging

In [2]: logging.warning('Watch out!')
WARNING:root:Watch out!

In [3]: logging.info('I told you so')

我想将根记录器的级别显式设置为INFO。我尝试使用name='root' 进行操作，但这没有明显效果：

In [4]: logging.getLogger('root').setLevel(logging.INFO)

In [5]: logging.info('I told you so')

如果我不带参数调用logging.getLogger()，我可以设置根记录器的级别：

In [6]: logging.getLogger().setLevel(logging.INFO)

In [7]: logging.info('I told you so')
INFO:root:I told you so

不过，我很好奇，为什么第一次没有成功？看起来这应该可以工作，因为它的name 属性是'root'：

In [12]: root_logger = logging.getLogger()

In [14]: root_logger.name
Out[14]: 'root'

简而言之，如果我不想依赖默认值，我会将什么名称传递给 logging.getLogger() 以获取根记录器？

Answer 1

根记录器的名称是root，但您不能通过名称访问根记录器。

检查logging.py 揭示了这一点：

def __init__(self, root):
    """
    Initialize the manager with the root node of the logger hierarchy.
    """
    self.root = root
    self.disable = 0
    self.emittedNoHandlerWarning = 0
    self.loggerDict = {}

root 与loggerDict 分开存储，这是所有命名记录器所在的位置。

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

你可以关注manager.getLogger内部函数，发现找不到root：

def getLogger(self, name):
        """
        Get a logger with the specified name (channel name), creating it
        if it doesn't yet exist. 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
        _acquireLock()
        try:
            if self.loggerDict.has_key(name):
                rv = self.loggerDict[name]
                if isinstance(rv, PlaceHolder):
                    ph = rv
                    rv = _loggerClass(name)
                    rv.manager = self
                    self.loggerDict[name] = rv
                    self._fixupChildren(ph, rv)
                    self._fixupParents(rv)
            else:
                rv = _loggerClass(name)
                rv.manager = self
                self.loggerDict[name] = rv
                self._fixupParents(rv)
        finally:
            _releaseLock()
        return rv

Answer 2

root logger 被访问：

logging.getLogger('')

示例代码：

logging.warning('Watch out!')
logging.getLogger('').setLevel(logging.INFO)
logging.info('I told you so')

输出：

  WARNING:root:Watch out!
  INFO:root:I told you so