why does python.subprocess hang after proc.communicate()?

Question

I\'ve got an interactive program called my_own_exe. First, it prints out alive, then you input S\\n and then it prints out alive

Answer 1

comunicate will only run once and then will close the pipe, therefore if you want to send several commands to it you need to send one after the other in the same string.

Here is an example that worked for me after some investigation, trying threads, subprocess32, stdin.write, stdout.read etc etc. This information is not in the official python reference information for communicate: https://docs.python.org/2/library/subprocess.html

The only place where I found this out was here: Python subprocess communicate kills my process

Here is the code, it is simple, no threads, no subprocess32, works on linux and windows. Yes you have to know how many times to send commands to the other process but in general you do know that. On top of this you can add threads, cwd, shell=True or anything else you may want but this is the simplest case:

def do_commands(self, cmd, parms):
    proc = subprocess.Popen(cmd,  stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE )

    # wait for the process to terminate
    out, err = process.communicate(cmd_parms)
    errcode = process.returncode

    return errcode, out, err

So for example if you want to send multiple carriage returns (\n) to the application being called and the a param in the middle (interactively mind you) you would call it something like this:

cmd_parms = "\n\n\n\n\nparm\n\n"

errcode, out, err = do_commands(command, cmd_parms)

Hope it helps.