Acquire an exclusive lock on a file (prevent two copies of a script running concurrently)

lock_file.py

# Lightly modified from: https://gist.github.com/kjpgit/ceab4fc029c778dd1675bea8592e3bc1
# Useful to ensure two copies of a script aren't running concurrently (assuming they use
# the same lock file, trying to lock it twice will raise IOError).
import fcntl

def _lock_file_exclusively(path):
    """
    Open @path and lock it exlusively.
    Return: file object, which you must maintain a reference to 
    (if it is closed, the lock is released).
    Raises: IOError on failure
    """
    print("Locking file %s" % path)
    lock_file = open(path)
    fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
    return lock_file