python logging 模块，logger.debug(),logger.info()等写入文件时的核心源码

最新推荐文章于 2025-06-16 11:14:12 发布

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最新推荐文章于 2025-06-16 11:14:12 发布

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本文将详细剖析Python logging模块中，logger.debug()、logger.info()等方法将日志写入文件的核心源码。通过理解关键函数emit()，了解如何格式化日志记录，并确保在不同编码环境下正确输出到文件。

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def emit(self, record):
        """
        Emit a record.

        If a formatter is specified, it is used to format the record.
        The record is then written to the stream with a trailing newline.  If
        exception information is present, it is formatted using
        traceback.print_exception and appended to the stream.  If the stream
        has an 'encoding' attribute, it is used to determine how to do the
        output to the stream.
        """
        try:
            msg = self.format(record)
            stream = self.stream
            fs = "%s\n"
            if not _unicode: #if no unicode support...
                stream.write(fs % msg)
            else:
                try:
                    if (isinstance(msg, unicode) and
                        getattr(stream, 'encoding', None)):
                        ufs = fs.decode(stream.encoding)
                        try:
                            stream.write(ufs % msg)
                        except UnicodeEncodeError:
                            #Printing to terminals sometimes fails. For example,
                            #with an encoding of 'cp1251', the above write will
                            #work if written to a stream opened or wrapped by
                            #the codecs module, but fail when writing to a
                            #terminal even when the codepage is set to cp1251.
                            #An extra encoding step seems to be needed.
                            stream.write((ufs % msg).encode(stream.encoding))
                    else:
                        stream.write(fs % msg)
                except UnicodeError:
                    stream.write(fs % msg.encode("UTF-8"))
            self.flush()
        except (KeyboardInterrupt, SystemExit):
            raise
        except:
            self.handleError(record)