LogRecord没有期望的字段

Question

在使用“日志记录”模块的Python中，文档保证LogRecord实例将具有许多属性，这些属性在文档中明确列出。

但是，似乎并非总是如此。当我不使用日志记录模块的'basicConfig（）'方法时，下面的程序显示在传递给LogHandler的'emit'方法的LogRecords中不存在属性'asctime'和'message'。

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上运行可以得到：

$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？

Answer 1

Formatter设置是负责的asctime，message因此在调用之前self.format(record)，这些属性是未定义的。从format方法的文档中：

记录的属性字典用作字符串格式化操作的操作数。返回结果字符串。在格式化字典之前，需要执行几个准备步骤。使用msg％args计算记录的message属性。如果格式化字符串包含“（asctime）”，则调用formatTime（）格式化事件时间。

由于您的示例代码未调用self.format(record)，因此可以预料，未定义这些属性。

有message和asctime设置，必须先调用self.format(record)内部emit方法。请试试

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")