Get realtime output from python subprocess

Question

I'm trying to invoke a command line utility from Python. The code is as follows

import subprocess
import sys

class Executor :

    def executeEXE(self,executable ) :

        CREATE_NO_WINDOW = 0x08000000
        process = subprocess.Popen(executable, stdout=subprocess.PIPE,
                                   creationflags=CREATE_NO_WINDOW )
        while True:
            line = process.stdout.readline()
            if line == '' and process.poll() != None:
                break
            print line

The problem with above code is I want the real-time output of above process which I'm not getting. What I'm doing wrong here.

The way `subprocess.popen()` output is echoed in [this answer](http://stackoverflow.com/a/4416529/355230) might be helpful. — martineau, Apr 03 '15 at 13:54
Here's [another couple of articles that won't help you](http://stackoverflow.com/q/2715847/4279) (it seems you are on Windows). At the very least use `iter()`-based loop instead of the `while`-loop. — jfs, Apr 03 '15 at 20:27
@Sebastian I think the `readline()` statement is somehow not returning the output. I'm not sure how `iter()` will help. And yes I'm on Windows. — Ganesh Satpute, Apr 04 '15 at 16:41

score 1 · Answer 1 · edited May 23 '17 at 11:43

1

there are 2 problems in your code:

first of all, readline() will block untill when a new line is printed out and flushed.
That means you should execute the code

while True:
...

in a new Thread and call a callback function when the output is ready.

Since the readline is waiting for a new line, you must use

print 'Hello World'
sys.stdout.flush()

everytime in your executable.

You can see some code and example on my git:
pyCommunicator

Instead, if your external tool is buffered, the only thing you can try is to use stderr as PIPE: https://stackoverflow.com/a/11902799/2054758

edited May 23 '17 at 11:43

Community

1
1

answered Apr 21 '15 at 15:49

user2054758

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Thanks for your answer :) I understand this problem but I can't find my way out of it. When I run the same executable on command line I can see real time output. And I know it enters newlines. And about second part I've tried that still that doesn't work out. That should mean process is buffering the output. Also if possible can I input commands on stdin of the new process and use it like shell? – Ganesh Satpute Apr 22 '15 at 16:51
yes, just put in your 'executable' variable an array of string command and args – user2054758 May 15 '15 at 13:12
No. I mean literally like shell.. To execute commands on shell, read output and do the same again.. – Ganesh Satpute May 16 '15 at 15:57

Get realtime output from python subprocess

1 Answers1