python_logging 日志处理流程

language_py summary_2018/12

1、py logger level=info 未输出info级别日志

1.1、原因

• root logger并未设置handler

import logging
root = logging.getLogger()
root.setLevel(logging.INFO)
root.info('this is info')
root.error('this is error')
// 输出
this is error

1.2、探究

• 根据源码研究输出error的整个流程
• 1、logger对日志级别的可见性判断

def error(self, msg, *args, **kwargs):
    """
    Log 'msg % args' with severity 'ERROR'.
    To pass exception information, use the keyword argument exc_info with
    a true value, e.g.
    logger.error("Houston, we have a %s", "major problem", exc_info=1)
    """
    # 判断可见性
    if self.isEnabledFor(ERROR):
        self._log(ERROR, msg, args, **kwargs)
def isEnabledFor(self, level):
    """
    Is this logger enabled for level 'level'?
    """
    # 如果logging模块设置了disable level，<=level则不可见
    if self.manager.disable >= level:
        return False
    return level >= self.getEffectiveLevel()
def getEffectiveLevel(self):
    """
    Get the effective level for this logger.
    Loop through this logger and its parents in the logger hierarchy,
    looking for a non-zero logging level. Return the first one found.
    """
    # 查找当前logger，如果未设置level,查找父节点的level，如果均无，返回NOTSET
    logger = self
    while logger:
        if logger.level:
            return logger.level
        logger = logger.parent
    return NOTSET
// 并没有发现问题，可以直接传递到handler进行处理

• 2、logger.handler的处理

// 生成record对象，放入handler中进行处理
def handle(self, record):
    """
    Call the handlers for the specified record.
    This method is used for unpickled records received from a socket, as
    well as those created locally. Logger-level filtering is applied.
    """
    # logger设置disabled是否传递给handler处理、filter过滤
    if (not self.disabled) and self.filter(record):
        self.callHandlers(record)
# 从当前logger对象和父logger对象查找handler，未找到
# 放入lastResort handler处理，但level为warn级别
def callHandlers(self, record):
    """
    Pass a record to all relevant handlers.
    Loop through all handlers for this logger and its parents in the
    logger hierarchy. If no handler was found, output a one-off error
    message to sys.stderr. Stop searching up the hierarchy whenever a
    logger with the "propagate" attribute set to zero is found - that
    will be the last logger whose handlers are called.
    """
    c = self
    found = 0
    while c:
        for hdlr in c.handlers:
            found = found + 1
            if record.levelno >= hdlr.level:
                hdlr.handle(record)
        if not c.propagate:
            c = None  # break out
        else:
            c = c.parent
    if (found == 0):
        if lastResort:
            if record.levelno >= lastResort.level:
                lastResort.handle(record)
        elif raiseExceptions and not self.manager.emittedNoHandlerWarning:
            sys.stderr.write("No handlers could be found for logger"
                             " \"%s\"\n" % self.name)
            self.manager.emittedNoHandlerWarning = True

1.3、结论

• python日志模块在没有handler进行处理的情况下，会将日志放入默认的lastResort handler处理，但level为warn级别，所以没有处理info级别。

// example
import logging
root = logging.getLogger()
# set logger level 为 INFO
root.setLevel(logging.INFO)
# set handler 
handler = logging.StreamHandler()
handler.setLevel(logging.INFO)
root.addHandler(handler)
root.info('this is info')
root.error('this is error')
//输出
this is info
this is error

1.4、参考

• logging — Python的日志记录工具
• Logging HOWTO