pygtk threads subprocess

import gtk
import os
import subprocess as sp
import time
import threading

gtk.gdk.threads_init()
#gobject.threads_init()

CMD = 'du -sh /home/lopz/'

class MainWin:
    """
    Creates a main window object
    """
    def __init__(self):
   w = gtk.Window()
   self.pb = gtk.ProgressBar()
   box = gtk.HBox(False, 0)
   self.btn_start = gtk.Button("Start")
   self.btn_start.connect("clicked", self.btn_start_click)
   box.pack_start(self.btn_start)
   btn_test = gtk.Button("Test")
   btn_test.connect("clicked", self.btn_test_click)
   box.pack_end(btn_test)

   self.btn_stop = gtk.Button("Stop")
   self.btn_stop.connect("clicked", self.btn_stop_click)
        self.btn_stop.set_sensitive(False)
   box.pack_end(self.btn_stop)

   box.pack_start(self.pb)

   w.add(box)
   w.show_all()
   w.connect("destroy", self.quit)

    def get_popen(self, cmd):
        return sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.STDOUT)
   
    def pulse(self):
   while not self.quit:
       time.sleep(0.1)
       gtk.gdk.threads_enter()
       self.pb.pulse()
       gtk.gdk.threads_leave()

    def exec_cmd(self):
   self.popen = self.get_popen(CMD.split())
   out = self.popen.stdout.read()
        if out:
            print out
            self.terminate()
       
    def terminate(self):
   self.quit = True
   os.kill(self.popen.pid, 9)
        self.btn_stop.set_sensitive(False)
        self.btn_start.set_sensitive(True)
        print "Terminate threads"

    def quit(self, widget):
   gtk.main_quit()
   self.terminate()

    def btn_test_click(self, widget):
   print "gtkMain thread"

    def btn_stop_click(self, widget):
   self.pb.set_text("Completed")
   self.terminate()

    def new_thread(self, method):
        t = threading.Thread(target=method, args=())
   t.start()


    def btn_start_click(self, widget):
   print "Start threads"
        self.quit = False
        self.btn_stop.set_sensitive(True)
        widget.set_sensitive(False)
        self.pb.set_text('Running')
        self.new_thread(self.pulse)
        self.new_thread(self.exec_cmd)
       
if __name__ == "__main__":
    gui = MainWin()
    gtk.gdk.threads_enter()
    gtk.main()
    gtk.gdk.threads_leave()