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From: Nobody <nobody@nowhere.invalid>
Newsgroups: comp.lang.python
Subject: Re: Unbuffered stderr in Python 3
Date: Tue, 03 Nov 2015 07:10:58 +0000
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On Mon, 02 Nov 2015 18:52:55 +1100, Steven D'Aprano wrote:

> In Python 2, stderr is unbuffered.
> 
> In most other environments (the shell, C...) stderr is unbuffered.
> 
> It is usually considered a bad, bad thing for stderr to be buffered. What
> happens if your application is killed before the buffer fills up? The
> errors in the buffer will be lost.
> 
> So how come Python 3 has line buffered stderr? And more importantly, how
> can I turn buffering off?

It's probably related to the fact that std{in,out,err} are Unicode
streams. 

	> type(sys.stderr)
	<class '_io.TextIOWrapper'>
	> type(sys.stderr.buffer)
	<class '_io.BufferedWriter'>
	> type(sys.stderr.buffer.raw)
	<class '_io.FileIO'>

It appears that you can turn it off with:

	sys.stderr = io.TextIOWrapper(sys.stderr.buffer.raw)
or:
	sys.stderr = io.TextIOWrapper(sys.stderr.detach().detach())

This results in a sys.stderr which appears to work and whose
.line_buffering property is False.