Python: How to read stdout of subprocess in a nonblocking way

Check select module

import subprocess
import select
import time
    
x=subprocess.Popen(['/bin/bash','-c',"while true; do sleep 5; echo yes; done"],stdout=subprocess.PIPE)
    
y=select.poll()
y.register(x.stdout,select.POLLIN)

while True:
  if y.poll(1):
     print x.stdout.readline()
  else:
     print "nothing here"
     time.sleep(1)

---

EDIT:

Threaded Solution for non posix systems:

import subprocess
from threading import Thread 
import time
 
linebuffer=[]
x=subprocess.Popen(['/bin/bash','-c',"while true; do sleep 5; echo yes; done"],stdout=subprocess.PIPE)

def reader(f,buffer):
   while True:
     line=f.readline()
     if line:
        buffer.append(line)
     else:
        break

t=Thread(target=reader,args=(x.stdout,linebuffer))
t.daemon=True
t.start()

while True:
  if linebuffer:
     print linebuffer.pop(0)
  else:
     print "nothing here"
     time.sleep(1)

As of python 3.5, you can use os.set_blocking() as follows.

import os
import subprocess

process = subprocess.Popen([path_to_exe, os.path.join(temp_dir,temp_file)], stdout=subprocess.PIPE)
os.set_blocking(process.stdout.fileno(), False) #<----- HERE
while True:   
    output=process.stdout.readline()
    print "test"


    if process.poll() is not None:
        break
rc = process.poll()