无需冲洗（）和换行即可在子流程输出上进行非阻塞读取

Question

I have a program that I can't modify. This program print data to stdout WITHOUT flushing it or put \\n inside and wait for input and so on.

My question is how can I, from a Python script, print in real-time stdout and write into his stdin ? I found some ways to write into his stdin without closing the programs but the problem remains for printing his stdout too.

In fact, there are some issues with thread, Popen and fcntl to print in real time his output but they all assumes that the program flush stdout after each print and include \\n in their output.

To be clear, let's say I have a program test.c :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main (void)
{
    char name[100], age[100], location[100];
    fprintf (stdout, "\nWhat is your name : ");
    fgets (name, sizeof (name), stdin);
    name[strcspn (name, "\n")] = '\0';
    fprintf (stdout, "How old are you : ");
    fgets (age, sizeof (age), stdin);
    age[strcspn (age, "\n")] = '\0';
    fprintf (stdout, "Where do you live : ");
    fgets (location, sizeof (location), stdin);
    location[strcspn (location, "\n")] = '\0';
    fprintf (stdout, "\nHello %s, you have %s years old and live in 
             %s\n\n", name, age, location);
    return 0;
}

How can I, from a Python script, output the first fprintf() then writing answer into his stdin and so on in the same way I could simply launch test.c ?

The purpose is to control data sent to this program from a script and still having return on what happens.

Answer 1

You may use the following program which is heavily relying on the subprocess package from the standard Python language:

def run_program(cmd, sinput=''):
    """Run the command line and output (ret, sout, serr)."""
    import subprocess

    proc =  subprocess.Popen(cmd,
                             stdin=subprocess.PIPE,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE)
    sin = proc.stdin
    sout, serr = proc.communicate(sinput.encode("utf-8"))
    ret = proc.wait()

    return (ret, sout, serr)

So, the program you just wrote in C would give the following:

cmd = ['myprogram']
sinput = 'myname\n6\nWhitechapel\n'
(ret, sout, serr) = run_program(cmd, sinput)

Note that you cannot avoid the \\n character simply because it is used by your target program to know that you send the answer to a question.