import threading
from subprocess import Popen, PIPE, STDOUT

class MyThread(threading.Thread):
    def run(self):
        print "before Popen"
        sp = Popen(["ls", "-al"], stdout=PIPE, stderr=STDOUT)
        print "before first line"
        for line in sp.stdout:
            print line[:-1]
        print "after last line"


t = MyThread()
t.start()