Question

Since input and raw_input() stop the program from running anymore, I want to use a subprocess to run this program…

while True: print raw_input()

and get its output.

This is what I have as my reading program:

import subprocess
process = subprocess.Popen('python subinput.py', stdout=subprocess.PIPE, stderr=subprocess.PIPE) 
while True:
    output=process.stdout.read(12)
    if output=='' and process.poll()!=None:
        break
    if output!='':
        sys.stdout.write(output)
        sys.stdout.flush()

When I run this, the subprocess exits almost as fast as it started. How can I fix this?

Answer 1

I’m afraid it won’t work this way.

You assume, that subprocess will attach your console (your special
case of stdin). This does not work, the module only has two
options for specifying that: PIPE and STDOUT.

When nothing is specified, the subprocess won’t be able to use
the corresponding stream – it’s output will go nowhere or it will
receive no input. The raw_input() ends because of EOF.

The way to go is to have your input in the “main” program,
and the work done in a subprocess.

EDIT:

Here’s an example in multiprocessing

from multiprocessing import Process, Pipe
import time

def child(conn):
    while True:
        print "Processing..."
        time.sleep(1)
        if conn.poll(0):
            output = conn.recv()
            print output
        else:
            print "I got nothing this time"

def parent():
    parent_conn, child_conn = Pipe()
    p = Process(target=child, args=(child_conn,))
    p.start()
    while True:
        data = raw_input()
        parent_conn.send(data)
    # p.join() - you have to find some way to stop all this...
    # like a specific message to quit etc.


if __name__ == '__main__':
    parent()

You of course need to make it more robust by finding a way too stop
this cooperation. In my example both processes are in the same file,
but you may organize it differently.

This example works on Linux, you may have some problems with pipes on Windows,
but it should be altogether solvable.

The “Processing” is the part where you want to do something else, not just
wait for the data from the parent.