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Re: Unbuffered stderr in Python 3

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From Terry Reedy <tjreedy@udel.edu>
Newsgroups comp.lang.python
Subject Re: Unbuffered stderr in Python 3
Date Tue, 3 Nov 2015 17:25:55 -0500
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On 11/3/2015 10:42 AM, Chris Angelico wrote:
> On Wed, Nov 4, 2015 at 2:00 AM, Random832 <random832@fastmail.com> wrote:
>> Nobody <nobody@nowhere.invalid> writes:
>>
>>> It's probably related to the fact that std{in,out,err} are Unicode
>>> streams.
>>
>> There's no fundamental reason a Unicode stream should have to be line
>> buffered. If it's "related", it's only in that an oversight was made in
>> the course of making that change.

The current behavior is not an 'oversight'.  I was considered, decided, 
and revisited in https://bugs.python.org/issue13601.  Guido: 
"Line-buffering should be good enough since in practice errors messages 
are always terminated by a newline."  If not, print(part_line, 
file=sys.stderr, flush=True) works for the unusual case.

> Yep. Unicode *input* streams need to be buffered, but *output* can
> always be insta-flushed. The only significance of Unicode to output is
> that a single character may cause multiple bytes to be output; and
> since output can block for even a single byte, it should be no
> different.
>
> +1 for making sys.stderr unbuffered.

-
Terry Jan Reedy

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Thread

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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