python: nonblocking subprocess, check stdout
- by Will Cavanagh
Ok so the problem I'm trying to solve is this:
I need to run a program with some flags set, check on its progress and report back to a server. So I need my script to avoid blocking while the program executes, but I also need to be able to read the output. Unfortunately, I don't think any of the methods available from Popen will read the output without blocking. I tried the following, which is a bit hack-y (are we allowed to read and write to the same file from two different objects?)
import time
import subprocess
from subprocess import *
with open("stdout.txt", "wb") as outf:
with open("stderr.txt", "wb") as errf:
command = ['Path\\To\\Program.exe', 'para', 'met', 'ers']
p = subprocess.Popen(command, stdout=outf, stderr=errf)
isdone = False
while not isdone :
with open("stdout.txt", "rb") as readoutf: #this feels wrong
for line in readoutf:
print(line)
print("waiting...\\r\\n")
if(p.poll() != None) :
done = True
time.sleep(1)
output = p.communicate()[0]
print(output)
Unfortunately, Popen doesn't seem to write to my file until after the command terminates.
Does anyone know of a way to do this? I'm not dedicated to using python, but I do need to send POST requests to a server in the same script, so python seemed like an easier choice than, say, shell scripting.
Thanks!
Will
