Python sys.stderr flush frequency
How often does sys.stderr flush its buffer, and is this standard among different environments?
>>> import sys
>>> sys.__stderr__
<open file '<stderr>', mode 'w' at 0x2b4fcb7ac270>
I see that it is just a standard file type, but I don't know what value of buffering it's supposed to be. dir() does not seem to yield any useful information either.
On Python 2, I can't find where in the documentation sys.stderr 's buffering is specified. I'd expect the same behaviour as stderr in C that is unbuffered (except Windows) and I don't know whether c99 standard mandates it. The standard error stream is not fully buffered in POSIX. -u option forces standard streams to be unbuffered in Python 2.
On Python 3:
When interactive, standard streams are line-buffered. Otherwise, they are block-buffered like regular text files. You can override this value with the -u command-line option.
-u command-line option:
Force the binary layer of the stdout and stderr streams (which is available as their buffer attribute) to be unbuffered. The text I/O layer will still be line-buffered if writing to the console, or block-buffered if redirected to a non-interactive file.
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