flock-stuff.py

import fcntl
LOCK_SH = fcntl.LOCK_SH  # shared lock
LOCK_NB = fcntl.LOCK_NB  # non-blocking
LOCK_EX = fcntl.LOCK_EX


# django helpers

def _fd(f):
    """Get a filedescriptor from something which could be a file or an fd."""
    return f.fileno() if hasattr(f, 'fileno') else f


def lock(f, flags):
    ret = fcntl.flock(_fd(f), flags)
    return ret == 0

def unlock(f):
    ret = fcntl.flock(_fd(f), fcntl.LOCK_UN)
    return ret == 0


f = open('/tmp/mylock', 'w')
try:
    lock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
except IOError as e:
    print('failed to get lock')
else:
    print('succeeded in getting lock')


# ...

unlock(f)
f.close()