Using Python pid to controll processes

python_pid.py

#!/usr/bin/python

import os
import time
import signal

# Get process PID
PID = str(os.getpid())

PIDFILE = "RUNNING.pid"

def can_it_run():

  # Check wether lock PIDFILE exists
  if os.path.isfile(PIDFILE):
    return False
  else:
    return True

def run():

  # Write lock file containing process PID
  file(PIDFILE, 'w').write(PID);
  print "Executing under PID " + PID
  
  try:
    # Simulating miscellaneous tasks
    time.sleep(60)
  finally:
    # removing lock file upon script execution
    os.unlink(PIDFILE)

if __name__ == '__main__':

  if can_it_run():
    run();
  else:
    # Retrieving PID of previous execution
    old_pid = ''.join(file("RUNNING.pid"))
    print "Script already running under PID %s, which is now being terminated." % old_pid

    # forcing a new execution by killing old process
    os.kill(int(old_pid),signal.SIGTERM)

    run()