That's how you limit CPU usage of a process using signal module

cpulimit.py

#!/usr/bin/env python

import time, os, sys, signal

sleeptime = waketime = 0.01

def send(signal, pids):
	for pid in pids:
		os.kill(pid, signal)

pids = map(int, sys.argv[1:])

while 1:
	send(signal.SIGSTOP, pids)
	try: time.sleep(sleeptime)
	except KeyboardInterrupt, e:
		send(signal.SIGCONT, pids)
		raise e

	send(signal.SIGCONT, pids)
	time.sleep(waketime)