python日志记录是否刷新每个日志？
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Does python logging flush every log?
提问by Vincent Xue
When I write a log to file using the standard module logging, will each log be flushed to disk separately? For example, will the following code flush log by 10 times?
当我使用标准模块logging将日志写入文件时，每个日志是否会分别刷新到磁盘？例如，以下代码会将日志刷新 10 次吗？
logging.basicConfig(level=logging.DEBUG, filename='debug.log')
for i in xrange(10):
logging.debug("test")
if so, will it slow down ?
如果是这样，它会变慢吗？
采纳答案by Bakuriu
Yes, it does flush the output at every call. You can see this in the source code for the StreamHandler:
是的，它会在每次调用时刷新输出。您可以在以下源代码中看到这一点StreamHandler：
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)
I wouldn't really mind about the performance of logging, at least not before profiling and discovering that it is a bottleneck. Anyway you can always create a Handlersubclass that doesn't perform flushat every call to emit(even though you will risk to lose a lot of logs if a bad exception occurs/the interpreter crashes).
我真的不介意日志记录的性能，至少在分析和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不会flush在每次调用时都执行的子类emit（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）。
