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Groups > comp.lang.python > #98135

Re: Unbuffered stderr in Python 3

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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.

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Unbuffered stderr in Python 3 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-02 18:52 +1100
  Re: Unbuffered stderr in Python 3 Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2015-11-02 11:48 +0100
  Re: Unbuffered stderr in Python 3 Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2015-11-02 11:54 +0100
  Re: Unbuffered stderr in Python 3 Nobody <nobody@nowhere.invalid> - 2015-11-03 07:10 +0000
    Re: Unbuffered stderr in Python 3 Random832 <random832@fastmail.com> - 2015-11-03 10:00 -0500
    Re: Unbuffered stderr in Python 3 Chris Angelico <rosuav@gmail.com> - 2015-11-04 02:42 +1100
    Re: Unbuffered stderr in Python 3 Terry Reedy <tjreedy@udel.edu> - 2015-11-03 17:25 -0500
      Re: Unbuffered stderr in Python 3 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-04 14:18 +1100
        Re: Unbuffered stderr in Python 3 Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2015-11-04 09:19 +0100
          Re: Unbuffered stderr in Python 3 Steven D'Aprano <steve@pearwood.info> - 2015-11-04 21:24 +1100
            Re: Unbuffered stderr in Python 3 Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2015-11-04 11:43 +0100
            Re: Unbuffered stderr in Python 3 Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2015-11-04 12:49 +0100
            Re: Unbuffered stderr in Python 3 Random832 <random832@fastmail.com> - 2015-11-04 08:43 -0500
        Re: Unbuffered stderr in Python 3 Terry Reedy <tjreedy@udel.edu> - 2015-11-04 18:00 -0500
  Re: Unbuffered stderr in Python 3 srinivas devaki <mr.eightnoteight@gmail.com> - 2015-11-06 19:10 +0530

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