freebsd/linux pidfile+lockfile

lockme.py

#!/usr/bin/env python

import os, fcntl, time

def locked(func):
    def wrapper(*args, **kwargs):
        with open('LOCKFILE','a+') as lf:
            try:
                fcntl.flock(lf.fileno(), fcntl.LOCK_EX|fcntl.LOCK_NB)
            except IOError:
                raise SystemExit('Cannot acquire lock')
            else:
                lf.truncate(0)
                lf.write('%d\n' % os.getpid())
                lf.flush()
                try:
                    func(*args, **kwargs)
                finally:
                    lf.truncate(0)
    return wrapper

@locked
def job(foo):
    print "Doing serious business"
    print foo
    time.sleep(15)
    print "Bye"

if __name__ == "__main__":
    job('yo, dawg!')

Thank you, I've updated the code with the snippet you suggested.