How to get output from subprocess.Popen(). proc.stdout.readline() blocks, no data prints out

Question

I want output from execute Test_Pipe.py, I tried following code on Linux but it did not work.

Test_Pipe.py

import time while True :     print "Someting ..."     time.sleep(.1) 

Caller.py

import subprocess as subp import time  proc = subp.Popen(["python", "Test_Pipe.py"], stdout=subp.PIPE, stdin=subp.PIPE)  while True :     data = proc.stdout.readline() #block / wait     print data     time.sleep(.1) 

The line proc.stdout.readline() was blocked, so no data prints out.

Answer 1

You obviously can use subprocess.communicate but I think you are looking for real time input and output.

readline was blocked because the process is probably waiting on your input. You can read character by character to overcome this like the following:

import subprocess import sys  process = subprocess.Popen(     cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE )  while True:     out = process.stdout.read(1)     if out == '' and process.poll() != None:         break     if out != '':         sys.stdout.write(out)         sys.stdout.flush()