Unbuffered stderr in Python 3
Terry Reedy
tjreedy at udel.edu
Tue Nov 3 17:25:55 EST 2015
On 11/3/2015 10:42 AM, Chris Angelico wrote:
> On Wed, Nov 4, 2015 at 2:00 AM, Random832 <random832 at fastmail.com> wrote:
>> Nobody <nobody at 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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