Python sys.stderr reset frequency

Question

How often does sys.stderr flush its buffer and is this the standard for different environments?

>>> import sys >>> sys.__stderr__ <open file '<stderr>', mode 'w' at 0x2b4fcb7ac270> 

I see that this is just a standard file type, but I don’t know what buffering value it should be. dir() also does not provide any useful information.

Answer 1

In Python 2, I cannot find where sys.stderr documentation buffering is sys.stderr . I would expect the same behavior as stderr in C, which is not buffered (except Windows) , and I don't know if the c99 standard matches. The standard error stream is not fully buffered on POSIX. -u causes standard threads to be unbuffered in Python 2.

In Python 3 :

In interactive mode, standard streams are buffered per line. Otherwise, they are buffered as regular text files. You can override this value with the -u command line -u .

-u command line option :

Set the binary level of stdout and stderr streams (which are available as a buffer attribute) to be unbuffered. The text I / O layer will still be line-buffered when written to the console or block-buffered if redirected to a non-interactive file.