python日志记录是否刷新每个日志？

Question

当我使用标准模块 logging 将日志写入文件时，每个日志会单独刷新到磁盘吗？ 比如下面的代码会刷新日志10次吗？

logging.basicConfig(level=logging.DEBUG, filename='debug.log')
    for i in xrange(10):
        logging.debug("test")

如果是这样，它会变慢吗？

Answer 1

是的，它确实会在每次调用时刷新输出。你可以在StreamHandler的源代码中看到这一点：

def flush(self):
    """
    Flushes the stream.
    """
    self.acquire()
    try:
        if self.stream and hasattr(self.stream, "flush"):
            self.stream.flush()
    finally:
        self.release()

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
        stream.write(msg)
        stream.write(self.terminator)
        self.flush()   # <---
    except (KeyboardInterrupt, SystemExit): #pragma: no cover
        raise
    except:
        self.handleError(record)

我不会真正介意日志记录的性能，至少在分析并发现它是一个瓶颈之前不会。无论如何，您始终可以创建一个 Handler 子类，它不会在每次调用 emit 时执行 flush（即使如果发生错误异常/解释器崩溃，您将面临丢失大量日志的风险）。