fnctl:lockf-vs-flock.py

import fcntl

# Expected output:
#  lock acquired
#  failed to lock
#  lock acquired

lf = '/tmp/some.lock'
h = None

def lock(path):
    global h
    try:
        # w is used so we don't re-use the same FD, this simulates as if separate programs are running this code
        w = None
        if not h:
            h = open(lf, 'w')
            w = h
        else:
            w = open(lf, 'w')
        fcntl.flock(w, fcntl.LOCK_EX | fcntl.LOCK_NB)
    except IOError:
        return False
    print 'lock acquired'
    return True

if not lock(lf):
    print 'failed to lock'

if not lock(lf):
    print 'failed to lock'

h.close()
if not lock(lf):
    print 'failed to lock'