Cómo mantener un script en ejecución

import sys
#Get the process id of this process
pid = os.getpid()
#Get the name of this script, as passed to the Python interpreter
myname = sys.argv[0]
#Run a ps command that includes the command lines of processes
ps = os.popen('ps --no-headers -elf|fgrep %s' % myname)
#Search for any processes that are running python and this script.  We check for
#python so that we don't bomb when, for example, someone's editing this script
#in vi.
for p in ps:
	if p.find('python')>-1 and p.find(myname)>-1:
		#If the pid of the process we've found is not the same as our pid,
		#then another instance is running.
		otherpid = int(p.split()[3])
		if otherpid <> pid: sys.exit()
ps.close()