subprocess: reading from stdout hangs process termination, waiting for ENTER keyboard signal

[Kushal Kumaran]

On Wed, Apr 15, 2009 at 1:20 PM, giohappy <giohappy at gmail.com> wrote:
> On 14 Apr, 18:52, MRAB <goo... at mrabarnett.plus.com> wrote:
>> giohappywrote:
>> > Hello everyone.
>> > I'm trying to use subprocess module to launch a Windows console
>> > application. The application prints some results to standard output
>> > and then waits for the user to press any key to terminte. I can't
>> > control this behaviour, as the application is not mine...
>> > I'm stuck at the very first lines of my code. I'm trying to force
>> > process termination (even with proc.terminate()), and it works only if
>> > I don't read from stdout. If I do proc.stdout.read() the process
>> > hangs, and I have to manually press the keyboard to interrupt it.
>> > Probably it's due a low-level handle that is kept on the process
>> > stdout, waiting for the keypress event...
>>
>> > How can I solve it?
>> > Giovanni
>>
>> > ------- Code excerpt-------
>>
>> > proc = subprocess.Popen('the_app.exe',
>> >                        shell=True,
>> >                        stdout=subprocess.PIPE,
>> >                        )
>> > #stdout_value = proc.communicate()[0]
>> > stdout_value = proc.stdout.read()
>> > PROCESS_TERMINATE = 1
>> > handle = win32api.OpenProcess(PROCESS_TERMINATE, False, proc.pid)
>> > win32api.TerminateProcess(handle, -1)
>> > win32api.CloseHandle(handle)
>> > print stdout_value
>>
>> Try this:
>>
>> proc = subprocess.Popen('the_app.exe',
>>                         shell=True,
>>                         stdin=subprocess.PIPE,
>>                         stdout=subprocess.PIPE,
>>                         )
>> stdout_value = proc.communicate("\n")[0]
>
> MRAB, I've tried that too but no result... I still have to press a
> keybord key to terminate (the classical "Press any key to continue")

If it actually is "Press any key to continue" rather than "Press Enter
to continue", it is likely directly using the console using available
low-level APIs, rather than reading from stdin.  AFAIK, subprocess
cannot handle that.

-- 
kushal