LogRecord 没有预期的字段

在使用“logging”模块的Python中，文档承诺LogRecord实例将具有许多属性，这些属性在文档中明确列出。

然而，情况似乎并不总是如此。当我不使用日志记录模块的“basicConfig()”方法时，下面的程序显示属性“asctime”和“message”不存在于传递给 LogHandler 的“emit”方法的 LogRecord 中。

import logging

class LoggingHandler(logging.Handler):
    def __init__(self):
        logging.Handler.__init__(self)
    def emit(self, record):
        assert isinstance(record, logging.LogRecord)
        print("LoggingHandler received LogRecord: {}".format(record))

        # List of LogRecord attributes expected when reading the
        # documentation of the logging module:

        expected_attributes = \
            "args,asctime,created,exc_info,filename,funcName,levelname," \
            "levelno,lineno,module,msecs,message,msg,name,pathname," \
            "process,processName,relativeCreated,stack_info,thread,threadName"

        for ea in expected_attributes.split(","):
            if not hasattr(record, ea):
                print("UNEXPECTED: LogRecord does not have the '{}' field!".format(ea))


loggingHandler = LoggingHandler()
rootLogger = logging.getLogger()
rootLogger.addHandler(loggingHandler)

# emit an WARNING message
logging.warning("WARNING MESSAGE")

在 Python 3 上运行它会给出：

$python3 test_logging.py
LoggingHandler received LogRecord: <LogRecord: root, 30, test_logging.py, 28, "WARNING MESSAGE">
UNEXPECTED: LogRecord does not have the 'asctime' field!
UNEXPECTED: LogRecord does not have the 'message' field!

这里发生了什么？我是否误解了文档？需要做什么来确保 LogRecord 实例具有承诺的“asctime”和“message”属性？

其责任是Formatter https://docs.python.org/3/library/logging.html#logging.Formatter to set asctime and message所以在打电话之前self.format(record)，这些属性是未定义的。从文档format https://docs.python.org/3/library/logging.html#logging.Formatter.format method:

记录的属性字典用作字符串的操作数 格式化操作。返回结果字符串。格式化前 字典中，执行了几个准备步骤。这 记录的消息属性是使用 msg % args 计算的。如果 格式化字符串包含“(asctime)”，调用 formatTime() 设置事件时间的格式。

由于您的示例代码未调用self.format(record)因此，这些属性未定义是预期的行为。

To have message and asctime设置，你必须先调用self.format(record)在 - 的里面emit方法。请尝试

import logging

class LoggingHandler(logging.Handler):
    def emit(self, record):
        assert isinstance(record, logging.LogRecord)
        print("LoggingHandler received LogRecord: {}".format(record))

        self.format(record)

        # List of LogRecord attributes expected when reading the
        # documentation of the logging module:

        expected_attributes = \
            "args,asctime,created,exc_info,filename,funcName,levelname," \
            "levelno,lineno,module,msecs,message,msg,name,pathname," \
            "process,processName,relativeCreated,stack_info,thread,threadName"

        for ea in expected_attributes.split(","):
            if not hasattr(record, ea):
                print("UNEXPECTED: LogRecord does not have the '{}' field!".format(ea))


formatter = logging.Formatter("%(asctime)s")
loggingHandler = LoggingHandler()
loggingHandler.setFormatter(formatter)
rootLogger = logging.getLogger()
rootLogger.addHandler(loggingHandler)

# emit an WARNING message
logging.warning("WARNING MESSAGE")