Unbuffered stderr in Python 3

[Steven D'Aprano]

On Wednesday 04 November 2015 09:25, Terry Reedy wrote:

> 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.

This is one of the offending line from our code base:

print('<4>Suspicious answer "{}"!'.format(answer), file=sys.stderr)

So that ought to be terminated by a newline. And yet, the stderr output 
doesn't show up until the program exits.




-- 
Steve