A platform independent file lock for Python
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Benedikt Schmitt
Latest commit b71c3a4 Oct 2, 2018

README.rst

py-filelock

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This package contains a single module, which implements a platform independent file lock in Python, which provides a simple way of inter-process communication:

from filelock import Timeout, FileLock

lock = FileLock("high_ground.txt.lock")
with lock:
    open("high_ground.txt", "a").write("You were the chosen one.")

Don't use a FileLock to lock the file you want to write to, instead create a separate .lock file as shown above.

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Animated example

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Installation

py-filelock is available via PyPi:

$ pip3 install filelock

Documentation

The documentation for the API is available on readthedocs.org.

Examples

A FileLock is used to indicate another process of your application that a resource or working directory is currently used. To do so, create a FileLock first:

from filelock import Timeout, FileLock

file_path = "high_ground.txt"
lock_path = "high_ground.txt.lock"

lock = FileLock(lock_path, timeout=1)

The lock object supports multiple ways for acquiring the lock, including the ones used to acquire standard Python thread locks:

with lock:
    open(file_path, "a").write("Hello there!")

lock.acquire()
try:
    open(file_path, "a").write("General Kenobi!")
finally:
    lock.release()

The acquire() method accepts also a timeout parameter. If the lock cannot be acquired within timeout seconds, a Timeout exception is raised.:

try:
    with lock.acquire(timeout=10):
        open(file_path, "a").write("I have a bad feeling about this.")
except Timeout:
    print("Another instance of this application currently holds the lock.")

The lock objects are recursive locks, which means that once acquired, they will not block on successive lock requests:

def cite1():
    with lock:
        open(file_path, "a").write("I hate it when he does that.")

def cite2():
    with lock:
        open(file_path, "a").write("You don't want to sell me death sticks.")

# The lock is acquired here.
with lock:
    cite1()
    cite2()

# And released here.

FileLock vs SoftFileLock

The FileLock is platform dependent while the SoftFileLock is not. Use the FileLock if all instances of your application are running on the same host and a SoftFileLock otherwise.

The SoftFileLock only watches the existence of the lock file. This makes it ultra portable, but also more prone to dead locks if the application crashes. You can simply delete the lock file in such cases.

Contributions

Contributions are always welcome. Never hesitate to open a new issue.

License

This package is public domain.