Python - GObject event, Threading, and Signal

#!/usr/bin/python
# coding: utf-8
import os, sys, time
import gobject      # need for gobject event timeout
import signal       # need for system signal.
import threading    # need for python thread.
#from dbus.mainloop.glib import DBusGMainLoop
reload(sys)
sys.setdefaultencoding('utf-8')

def g_event_timer(*args):
    # for gobject.timeout_add(). it's gobject-style thread.
    # note: there are three kind of basic event source.
    print("1. g_event_timer tick.")
    return True  # keep interval

def sys_signal_timer(*args):
    # for system Signal
    print("2. sys_signal_timer tick.")

def thread_timer_func(*args):
    # for threading.Timer
    while True:
        print("3. thread_timer tick.")
        time.sleep(2)

def terminate_gobject_loop(signum, func):
    loop.quit()

signal.signal(signal.SIGINT,  terminate_gobject_loop)

gobject.threads_init()            # required for gobject collaborate with python thread.
#DBusGMainLoop(set_as_default=True) # if you use DBus.
#dbus.mainloop.glib.threads_init() # required for dbus collaborate with python thread.
loop = gobject.MainLoop()

# enable g_event_timer tick.
gobject.timeout_add(2000, g_event_timer)

# enable sys_signal_timer tick.
signal.signal(signal.SIGALRM, sys_signal_timer)
signal.setitimer(signal.ITIMER_REAL, 2, 2)
signal.siginterrupt(signal.SIGALRM, False)  # not really work.

# enable thread_timer tick.
thread_timer = threading.Timer(2, thread_timer_func)
thread_timer.start()

print("PID: %d" % os.getpid())
print("Press Ctrl+C will quit g_event_timer.")
try:
    loop.run()
except:
    print("Unknown error. It breaks eventloop.")

signal.signal(signal.SIGALRM, signal.SIG_IGN)  # cancel signal_timer.

print("Wait 5 seconds.")
print("Quit g_event_timer.")
print("Ignore signal_timer.")
print("Only thread_timer tick.")
time.sleep(5)
# 1. g_event_timer will not tick.
# 2. if I don't cancel signal_timer, signal_timer will tick and interrupt sleep.
# 3. thread_timer will still tick.

print("End")
os._exit(0)