A file locker that uses the context manager.

flock.py

import fcntl


class FileLock:
    def __init__(self, filename, lock_type):
        self.fh = open(filename, "a")
        self.lock_type = lock_type

    def __enter__(self):
        print "Acquiring lock"
        fcntl.flock(self.fh.fileno(), self.lock_type)

    def __exit__(self, type, value, tb):
        print "Releasing lock"
        fcntl.flock(self.fh.fileno(), fcntl.LOCK_UN)
        self.fh.close()


def main():
    import os
    import time

    with FileLock("/tmp/some_lock_file", fcntl.LOCK_EX):
        print "Start: %s" % time.ctime()
        print "PID: %s" % os.getpid()
        time.sleep(5)
        print "Finish: %s" % time.ctime()

if __name__ == '__main__':
    main()