On 2008-12-23, s...@pobox.com <s...@pobox.com> wrote:
> Grant> Are you sure it's not Python buffering its input? Have you tried
> Grant> "python -u mympstat.py"?
>
> >> Nope. -u unbuffers stdout and stderr, not stdin. It really must be
> >> mpstat being uncooperative.
>
> Grant> That's not what my python man page says:
>
> Grant> -u Force stdin, stdout and stderr to be totally
> Grant> unbuffered. On systems where it matters, also put
> Grant> stdin, stdout and stderr in binary mode.
>
> Grant> That's for 2.5.2, but that's how I remember previous versions
> Grant> working as well.
>
> I'm still running 2.4.5 at work. It's -u help:
>
> -u : unbuffered binary stdout and stderr (also PYTHONUNBUFFERED=x)
> see man page for details on internal buffering relating to '-u'
>
> Was stdin unbuffering maybe added in 2.5?
Let's do some experiments...
$ cat echo.py
import sys
while 1:
line = sys.stdin.readline()
sys.stdout.write(line)
$ (while sleep 1; do date; done) | python2.4 echo.py
[I see a line printed once per second.]
$ (while sleep 1; do date; done) | python2.5 echo.py
[same as 2.4]
Is python stdin is line-buffered by default? We'll do a
version that doesn't have newlines in the input stream...
$ cat echo2.py
import sys
while 1:
sys.stdout.write(sys.stdin.read(1))
$ (while sleep 1; do echo -n $(date); done) | python2.4 echo2.py
[wait 10-20 seconds -- no output. When I hit ctrl-C, I see a
all the output.]
$ (while sleep 1; do echo -n $(date); done) | python2.5 echo2.py
[same as 2.4]
It appears the by default both 2.4 and 2.5 have line-buffered
stdin.
Let's try -u...
$ (while sleep 1; do echo -n $(date); done) | python2.4 -u echo2.py
[I see output once per second.]
$ (while sleep 1; do echo -n $(date); done) | python2.5 -u echo2.py
[same as 2.4]
Under Linux, the '-u' option unbuffers stdin in both 2.4 and
2.5. It just isn't mentioned in the help output or the man
page for 2.4.
--
Grant Edwards grante Yow! Will the third world
at war keep "Bosom Buddies"
visi.com off the air?
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