how to flush child_stdin

[joelcarrier@gmail.com]

I'm opening up a subprocess like this where slave.py is a text based
app that receives commands and responds with output:

r, w, e = popen2.popen3(' python slave.py')

I need to send slave.py a command and see the output,
so I'll do something like:

w.write("comman d here")
then i'll try this:
w.flush()

A separate thread is reading from r to retrieve output of slave.py.

The problem is that slave.py doesn't seem to receive commands unless I
also do:
w.close()

But I don't want to do this because I'll want to send more commands.

Any idea what is going on?

[joelcarrier@gmail.com]

Re: how to flush child_stdin

On Feb 22, 12:15 am, Dennis Lee Bieber <wlfr...@ix.net com.comwrote:

On Thu, 21 Feb 2008 12:34:28 -0800 (PST), "joelcarr...@gm ail.com"
<joelcarr...@gm ail.comdeclaime d the following in comp.lang.pytho n:
>
>
>

I'm opening up a subprocess like this where slave.py is a text based
app that receives commands and responds with output:

>

r, w, e = popen2.popen3(' python slave.py')

>

I need to send slave.py a command and see the output,
so I'll do something like:

>

w.write("comman d here")
then i'll try this:
w.flush()

>

A separate thread is reading from r to retrieve output of slave.py.

>

The problem is that slave.py doesn't seem to receive commands unless I
also do:
w.close()

>
What happens if you do:
>
w.write("comman d here\n")
w.flush()
>
Could the slave be blocked waiting for an EOL character before
processing said command?
--
Wulfraed Dennis Lee Bieber KD6MOG
wlfr...@ix.netc om.com wulfr...@bestia ria.com

HTTP://wlfraed.home.netcom.com/

(Bestiaria Support Staff: web-a...@bestiaria. com)
HTTP://www.bestiaria.com/

I don't think that is the problem, I'm feeding it newline characters.

[joelcarrier@gmail.com]

Re: how to flush child_stdin

On Feb 22, 2:01 pm, Dennis Lee Bieber <wlfr...@ix.net com.comwrote:

On Fri, 22 Feb 2008 08:35:03 -0800 (PST), "joelcarr...@gm ail.com"
<joelcarr...@gm ail.comdeclaime d the following in comp.lang.pytho n:
>

I don't think that is the problem, I'm feeding it newline characters.

>
It wasn't shown in your sample, so I jumped on the first likely
thing...
>
The second is in the hands of the subprocess... While you are
flushing output /to/ the subprocess, is IT flushing its output (the
stuff you are trying to read). A common problem seems to be that, as
soon as the process detects a pipe, it goes to buffered I/O, and if the
buffer isn't filled, the parent has no access...
--
Wulfraed Dennis Lee Bieber KD6MOG
wlfr...@ix.netc om.com wulfr...@bestia ria.com

HTTP://wlfraed.home.netcom.com/

(Bestiaria Support Staff: web-a...@bestiaria. com)
HTTP://www.bestiaria.com/

I'm actually running something like : r, w, e = popen2.popen3(' python -
u slave.py')
to try and force unbuffered. slave.py is basically outputting by
using print.
I guess it might still be buffering?
Anyway, thanks for your thoughts... I may have to take an entirely
difference approach. I was hoping not to have to touch the code base
represented by slave.py.

[Gabriel Genellina]

Re: how to flush child_stdin

En Fri, 22 Feb 2008 17:53:55 -0200, joelcarrier@gma il.com
<joelcarrier@gm ail.comescribió :

On Feb 22, 2:01 pm, Dennis Lee Bieber <wlfr...@ix.net com.comwrote:

>On Fri, 22 Feb 2008 08:35:03 -0800 (PST), "joelcarr...@gm ail.com"
><joelcarr...@g mail.comdeclaim ed the following in comp.lang.pytho n:
>>

I don't think that is the problem, I'm feeding it newline characters.

>>
> It wasn't shown in your sample, so I jumped on the first likely
>thing...
>>
> The second is in the hands of the subprocess... While you are
>flushing output /to/ the subprocess, is IT flushing its output (the
>stuff you are trying to read). A common problem seems to be that, as
>soon as the process detects a pipe, it goes to buffered I/O, and if the
>buffer isn't filled, the parent has no access...

>
I'm actually running something like : r, w, e = popen2.popen3(' python -
u slave.py')

That was not on your posted example either...

to try and force unbuffered. slave.py is basically outputting by
using print.
I guess it might still be buffering?
Anyway, thanks for your thoughts... I may have to take an entirely
difference approach. I was hoping not to have to touch the code base
represented by slave.py.

[master.py]

import popen2
r, w, e = popen2.popen3(' python -u slave.py')

w.write('comman d 1\n')
w.flush()
print r.readline()
w.write('comman d 2\n')
w.flush()
print r.readline()
w.write('\n')
w.flush()
print r.readline()

[slave.py]

while True:
line = raw_input().str ip()
if not line:
print "bye!"
break
print "echo:",lin e

That works OK for me on Windows XP.

--
Gabriel Genellina