Question

We have:

• A Python based server (A)
• A running command-line application (on the same Linux machine) which is able to read stdin, computes something and provides the output into stdout (B)

What is the best (most elegant) way how to send an input from (A) to stdin of (B), and wait for an answer from (B), i.e read its stdout?

Answer 1

As @Deestan pointed subprocess,module, is an elegant and proven one. We use subprocess a lot when we have to run commands from python.

Ours mostly involves running a command, mostly in-house built, and capturing its output. Our wrapper to run such commands looks thus.

import subprocess
def _run_command( _args, input=[],withShell=False):
    """
    Pass args as array, like ['echo', 'hello']
    Waits for completion and returns
    tuple (returncode, stdout, stderr)
    """
    p = subprocess.Popen(_args, shell = withShell,
                         stdin=subprocess.PIPE, stdout=subprocess.PIPE)
    [p.stdin.write(v) for v in input]
    stdout, stderr = p.communicate()
    return p.returncode, stdout, stderr

_,op,er = _run_command(['cat'],["this","is","for","testing"])
value="".join(op)
print value

_,op,er = _run_command(['ls',"/tmp"])
value="".join(op)
print value

If your input to B is minimal then subprocess is a yes.