Communicating with a running process

问题

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?

回答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.

回答2:

If you spawn (B) using Python's subprocess module from the standard library, you can set up (B)'s stdin and stdout as byte buffers readable and writable by (A).

b = Popen(["b.exe"], stdin=PIPE, stdout=PIPE)
b.stdin.write("OHAI\n")
print(b.stdout.readline())

For your given example, it's easiest to use communicate, as that takes care to avoid deadlocks for you:

b = Popen(["b.exe"], stdin=PIPE, stdout=PIPE)
b_out = b.communicate("OHAI\n")[0]
print(b_out)

http://docs.python.org/release/3.1.3/library/subprocess.html

http://docs.python.org/release/3.1.3/library/subprocess.html#subprocess.Popen.communicate

If there's a lot of 2-way communication, you should take care to avoid deadlocks because of full buffers. If your communication pattern gives this type of problem, you should consider using socket communication instead.

来源：https://stackoverflow.com/questions/10188389/communicating-with-a-running-process

标签

python

ipc