Simple python file locking context manager example on linux using python stdlib's `fcntl.flock`

locked_open.py

import logging
import fcntl
from contextlib import contextmanager

@contextmanager
def locked_open(filename, mode='r'):
    """locked_open(filename, mode='r') -> <open file object>
    
       Context manager that on entry opens the path `filename`, using `mode`
       (default: `r`), and applies an advisory write lock on the file which
       is released when leaving the context. Yields the open file object for
       use within the context.

       Note: advisory locking implies that all calls to open the file using
       this same api will block for both read and write until the lock is
       acquired. Locking this way will not prevent the file from access using
       any other api/method.
    """
    with open(filename, mode) as fd:
        fcntl.flock(fd, fcntl.LOCK_EX)
        logging.debug('acquired lock on %s', filename)
        yield fd
        # raw_input('press enter to release lock ')
        logging.debug('releasing lock on %s', filename)
        fcntl.flock(fd, fcntl.LOCK_UN)