fn, lno, func = self.findCaller()  

        f = currentframe()  #f是frame對象，每個方法調用生成一個frame對象，放在程序堆棧中。
        if f is not None:
            f = f.f_back
        rv = "(unknown file)", 0, "(unknown function)"
        while hasattr(f, "f_code"):
            co = f.f_code   #獲取code對象，它包含filename屬性，funcname屬性
            filename = os.path.normcase(co.co_filename)
            if filename == _srcfile:  #_srcfile是這個模塊文件自己的文件名，當文件名不再相同時
                f = f.f_back          # 得到外部調用者的frame，這就是需要的。
                continue
            rv = (filename, f.f_lineno, co.co_name)
            break
        return rv

def currentframe():
    """Return the frame object for the caller's stack frame."""
    try:
        raise Exception    #拋出異常，將生成traceback對象，其中包含frame對象。
    except:
        #sys.exc_traceback.tb_frame當前的frame， f_back調用著的frame
        return sys.exc_traceback.tb_frame.f_back
#sys._getframe(3)返回的并不是當前的frame，3應該是計算好了的，減少循環的次數，返回的是logger.error()的frame
if hasattr(sys, '_getframe'): currentframe = lambda: sys._getframe(3)

root = RootLogger(WARNING)     #RootLogger類是Logger的子類，無特殊功能，只是定義名字為‘root'。
Logger.root = root
Logger.manager = Manager(Logger.root)

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

    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
        _acquireLock()
        try:
            if name in self.loggerDict:
                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