py-filelock

py-filelock is a single Python module, which implements a platform independent file lock. The lock is thread safe and easy to use:

lock = filelock.FileLock("my_lock_file")
with lock:
    shutil.copy("...", "...")

The lock implements also a counter, which allows you to acquire the lock multiple times without blocking:

lock = filelock.FileLock("my_lock_file")

def update_files1():
    with lock:
        assert lock.is_locked
        # ...
    return None

def update_files2():
    with lock:
        assert lock.is_locked
        # ...
    return None

def update_all_files():
    with lock:
        assert lock.is_locked

        update_files1()

        assert lock.is_locked

        update_files2()

        assert lock.is_locked
    assert not lock.is_locked
    return None

update_all_files()

Installation

This package is listed on PyPi, so you’re done with:

$ pip3 install filelock

Examples

import filelock

lock = filelock.FileLock("my_lock_file")

# Simply use the lock into a with statement.
with lock:
    pass

# If you want to set a timeout parameter, you can do it by:
with lock.acquire(timeout = 10):
    pass

# You can also set a default timeout value, which is used, when no
# special timeout value is given to the *acquire()* method:
lock.timeout = 20

with lock: # 20s timeout
    pass

with lock.acquire() # 20s timeout
    pass

with lock.acquire(timeout = 10) # 10s timeout
    pass

# If you can not use the *with* statement, use a try-finally construct
# instead:
lock.acquire()
try:
    pass
finally:
    lock.release()

# If you want to use a timeout value, you should consider to catch
# a Timeout exception:
try:
    with lock.acquire(timeout = 10):
        pass
except filelock.Timeout:
    pass

# If you can not use the with statement, you can again use a try-final
# construct instead.
try:
    lock.acquire()
except filelock.Timeout:
    pass
else:
    try:
        pass
    finally:
        lock.release()

# Please note, that you can acquire the lock multiple times without
# blocking. The lock will count, how often it has been acquired and releases
# the lock, as soon as the counter is 0.
with lock:
    assert lock.is_locked
    with lock:
        assert lock.is_locked
    assert lock.is_locked
assert (not lock.is_locked)

API

A platform independent file lock that supports the with-statement.

class filelock.BaseFileLock(lock_file, timeout=-1)

Bases: object

Implements the base class of a file lock.

acquire(timeout=None, poll_intervall=0.05)

Acquires the file lock or fails with a Timeout error.

# You can use this method in the context manager (recommended)
with lock.acquire():
    pass

# Or you use an equal try-finally construct:
lock.acquire()
try:
    pass
finally:
    lock.release()

Parameters:

• timeout (float) – The maximum time waited for the file lock. If timeout <= 0, there is no timeout and this method will block until the lock could be acquired. If timeout is None, the default timeout is used.

• poll_intervall (float) – We check once in poll_intervall seconds if we can acquire the file lock.

Raises:

Timeout – if the lock could not be acquired in timeout seconds.

Changed in version 2.0.0: This method returns now a proxy object instead of self, so that it can be used in a with statement without side effects.

property is_locked

True, if the object holds the file lock.

Changed in version 2.0.0: This was previously a method and is now a property.

property lock_file

The path to the lock file.

release(force=False)

Releases the file lock.

Please note, that the lock is only completly released, if the lock counter is 0.

Also note, that the lock file itself is not automatically deleted.

Parameters:

force (bool) – If true, the lock counter is ignored and the lock is released in every case.

property timeout

You can set a default timeout for the filelock. It will be used as fallback value in the acquire method, if no timeout value (None) is given.

If you want to disable the timeout, set it to a negative value.

A timeout of 0 means, that there is exactly one attempt to acquire the file lock.

New in version 2.0.0.

filelock.FileLock

Alias for the lock, which should be used for the current platform. On Windows, this is an alias for WindowsFileLock, on Unix for UnixFileLock and otherwise for SoftFileLock.

class filelock.SoftFileLock(lock_file, timeout=-1)

Bases: BaseFileLock

Simply watches the existence of the lock file.

exception filelock.Timeout(lock_file)

Bases: TimeoutError

Raised when the lock could not be acquired in timeout seconds.

lock_file

The path of the file lock.

class filelock.UnixFileLock(lock_file, timeout=-1)

Bases: BaseFileLock

Uses the fcntl.flock() to hard lock the lock file on unix systems.

class filelock.WindowsFileLock(lock_file, timeout=-1)

Bases: BaseFileLock

Uses the msvcrt.locking() function to hard lock the lock file on windows systems.

License

py-filelock is public domain:

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to <http://unlicense.org>

GitHub

This module is hosted on GitHub. If you have any questions or suggestions, don’t hesitate to open a new issue :).