Flushing stdout

[Graham Ashton]

Hi. I'm having trouble flushing sys.stdout. I've written a small example
to illustrate my problem (see below). In short, I expect it to ping
"received hello", sleep for 5 seconds and then print "received world".
Instead I get nothing for 5 seconds and then both statements pop out at
once.

As you'll no doubt gather from the example, the problem I'm really trying
to solve is sending message back from one process to another via a pipe.
Changing the buffering option in the os.pipe() call doesn't have any
effect either.

Any thoughts? Thanks.

P.S. I've not found -u and PYTHONUNBUFFERE D to help me.

P.P.S. I'm running 2.3.3 on Linux, libc 2.2.5-11.5.

---cut---
#!/usr/bin/env python

import os, sys, time

if len(sys.argv) > 1:
sys.stdout.writ e("hello\n")
sys.stdout.flus h()
time.sleep(5)
sys.stdout.writ e("world\n")
else:
command = "python %s foo" % os.path.basenam e(sys.argv[0])
for line in os.popen(comman d, "r", 1):
print "received", line,

[Steve Holden]

Re: Flushing stdout

Graham Ashton wrote:[color=blue]
> Hi. I'm having trouble flushing sys.stdout. I've written a small example
> to illustrate my problem (see below). In short, I expect it to ping
> "received hello", sleep for 5 seconds and then print "received world".
> Instead I get nothing for 5 seconds and then both statements pop out at
> once.
>[/color]
You aren't actually having trouble flushing sys.stdout at all ...
[color=blue]
> As you'll no doubt gather from the example, the problem I'm really trying
> to solve is sending message back from one process to another via a pipe.
> Changing the buffering option in the os.pipe() call doesn't have any
> effect either.
>[/color]
Nope. The holdup is elsewhere.
[color=blue]
> Any thoughts? Thanks.
>
> P.S. I've not found -u and PYTHONUNBUFFERE D to help me.
>[/color]
Nope, they won't ...
[color=blue]
> P.P.S. I'm running 2.3.3 on Linux, libc 2.2.5-11.5.
>
> ---cut---
> #!/usr/bin/env python
>
> import os, sys, time
>
> if len(sys.argv) > 1:
> sys.stdout.writ e("hello\n")
> sys.stdout.flus h()
> time.sleep(5)
> sys.stdout.writ e("world\n")
> else:
> command = "python %s foo" % os.path.basenam e(sys.argv[0])
> for line in os.popen(comman d, "r", 1):
> print "received", line,
>[/color]
The iteration over the pipe's contents is waiting until it sees the end
of the output before it yields anything. Try this:

import os, sys, time

if len(sys.argv) > 1:
sys.stdout.writ e("hello\n")
sys.stdout.flus h()
time.sleep(5)
sys.stdout.writ e("world\n")
else:
command = "python %s foo" % os.path.basenam e(sys.argv[0])
f = os.popen(comman d, "r", 1)
while 1:
line = f.readline()
if not line:
break
print "received", line,

You can probably find a tidier way to bundle this now you know what's up.

regards
Steve
--

http://www.holdenweb.com

http://pydish.holdenweb.com

Holden Web LLC +1 800 494 3119

[Graham Ashton]

Re: Flushing stdout

On Mon, 01 Nov 2004 16:41:04 -0500, Steve Holden wrote:
[color=blue]
> Graham Ashton wrote:[color=green]
>> Hi. I'm having trouble flushing sys.stdout.[/color]
> You aren't actually having trouble flushing sys.stdout at all ...
>[color=green]
>> As you'll no doubt gather from the example, the problem I'm really trying[/color]
>
> The iteration over the pipe's contents is waiting until it sees the end
> of the output before it yields anything.[/color]

Genius. Thanks Steve, much appreciated. Now I can actually send our users
some feedback...

Graham