how to flush child_stdin

Gabriel Genellina gagsl-py2 at
Tue Feb 26 04:11:07 CET 2008

En Fri, 22 Feb 2008 17:53:55 -0200, joelcarrier at  
<joelcarrier at> escribió:
> On Feb 22, 2:01 pm, Dennis Lee Bieber <wlfr... at> wrote:
>> On Fri, 22 Feb 2008 08:35:03 -0800 (PST), "joelcarr... at"
>> <joelcarr... at> declaimed the following in comp.lang.python:
>> > 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')

That was not on your posted example either...

> to try and force unbuffered. 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


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

w.write('command 1\n')
print r.readline()
w.write('command 2\n')
print r.readline()
print r.readline()


while True:
   line = raw_input().strip()
   if not line:
     print "bye!"
   print "echo:",line

That works OK for me on Windows XP.

Gabriel Genellina

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