Python subprocess and user interaction

Question

I'm working on a GUI front end in Python 2.6 and usually it's fairly simple: you use subprocess.call() or subprocess.Popen() to issue the command and wait for it to finish or react to an error. What do you do if you have a program that stops and waits for user interaction? For example, the program might stop and ask the user for an ID and password or how to handle an error?

c:\> parrot
Military Macaw - OK
Sun Conure - OK
African Grey - OK
Norwegian Blue - Customer complaint!
(r) he's Resting, (h) [Hit cage] he moved, (p) he's Pining for the fjords

So far everything I've read tells you how to read all output from a program only after it's finished, not how to deal with output while the program is still running. I can't install new modules (this is for a LiveCD) and I'll be dealing with user input more than once.

Answer 1

Check out the subprocess manual. You have options with subprocess to be able to redirect the stdin, stdout, and stderr of the process you're calling to your own.

from subprocess import Popen, PIPE, STDOUT

p = Popen(['grep', 'f'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)

grep_stdout = p.communicate(input='one\ntwo\nthree\nfour\nfive\nsix\n')[0]
print grep_stdout

You can also interact with a process line by line. Given this as prog.py:

import sys
print 'what is your name?'
sys.stdout.flush()
name = raw_input()
print 'your name is ' + name
sys.stdout.flush()

You can interact with it line by line via:

>>> from subprocess import Popen, PIPE, STDOUT
>>> p = Popen(['python', 'prog.py'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)
>>> p.stdout.readline().rstrip()
'what is your name'
>>> p.communicate('mike')[0].rstrip()
'your name is mike'