Python file lock module

filelock#

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: with open("high_ground.txt", "a") as f: f.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.

Similar libraries#

• the pid 3rd party library,
• for Windows the msvcrt module in the standard library,
• for UNIX the fcntl module in the standard library,
• the flufl.lock 3rd party library.

Installation#

filelock is available via PyPI, so you can pip install it:

python -m pip install filelock

Tutorial#

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: with open(file_path, "a") as f: f.write("Hello there!") lock.acquire() try: with open(file_path, "a") as f: f.write("General Kenobi!") finally: lock.release() @lock def decorated(): print("You're a decorated Jedi!") decorated() 

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): with open(file_path, "a") as f: f.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: with open(file_path, "a") as f: f.write("I hate it when he does that.") def cite2(): with lock: with open(file_path, "a") as f: f.write("You don't want to sell me death sticks.") # The lock is acquired here. with lock: cite1() cite2() # And released here. 

Logging#

All log messages by this library are made using the DEBUG_ level , under the filelock name. On how to control displaying/hiding that please consult the logging documentation of the standard library. E.g. to hide these messages you can use:

logging.getLogger("filelock").setLevel(logging.INFO) 

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 platform 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.

Asyncio support#

This library currently does not support asyncio. We’d recommend adding an asyncio variant though if someone can make a pull request for it, see here.

FileLocks and threads#

By default the FileLock internally uses threading.local to ensure that the lock is thread-local. If you have a use case where you’d like an instance of FileLock to be shared across threads, you can set the thread_local parameter to False when creating a lock. For example:

lock = FileLock("test.lock", thread_local=False) # lock will be re-entrant across threads # The same behavior would also work with other instances of BaseFileLock like SoftFileLock: soft_lock = SoftFileLock("soft_test.lock", thread_local=False) # soft_lock will be re-entrant across threads. 

Behavior where FileLock is thread-local started in version 3.11.0. Previous versions, were not thread-local by default.

Note: If disabling thread-local, be sure to remember that locks are re-entrant: You will be able to acquire the same lock multiple times across multiple threads.

Contributions and issues#

Contributions are always welcome, please make sure they pass all tests before creating a pull request. This module is hosted on GitHub. If you have any questions or suggestions, don’t hesitate to open a new issue 😊. There’s no bad question, just a missed opportunity to learn more.

Источник

Importance of Filelock and how to use that in Python

We need the filelock module in Python to prevent race conditions in concurrent and multi-process applications. Race conditions occur when multiple processes or threads access the same resource simultaneously and the outcome of the application depends on which process finishes first. For example, consider a scenario where multiple processes write to the same file. If two processes try to write to the file simultaneously, the second process may overwrite the changes made by the first process, leading to data corruption and incorrect results.

To install filelock

Simple Example of filelock module to lock a file in Python:

import os from filelock import Filelock lock = FileLock("file.lock") with lock: with open("file.txt", "a") as f: f.write(f"Line written by process  os.getpid()>\n") 

Here, You can name your lockfile anything you want, in our case, it is file.lock. This file will temporally create while acquiring the lock and it will automatically deleted after releasing the lock.
we use the FileLock class from the filelock module to lock the file file.lock. The with statement is used to obtain the lock and automatically release it after the protected code has executed. This ensures that only one process can access the file at a time and prevents race conditions. The os.getpid() function is used to obtain the process ID, which is written to the file along with the line of text. This allows us to see which process wrote each line to the file.

Summary

The filelock module provides a simple and reliable way to lock files and prevent race conditions. By using a lock file, you can ensure that only one process can access a shared resource at a time, and prevent data corruption and other issues that can occur when multiple processes access the same resource simultaneously. The filelock module is a great tool for developing concurrent and multi-process applications in Python, and it provides a simple and reliable way to lock files and prevent race conditions. “Recently I had to work with filelock but I take some help from AI to understand and Implement this in my project.”

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filelock#

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: with open("high_ground.txt", "a") as f: f.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.

Similar libraries#

• the pid 3rd party library,
• for Windows the msvcrt module in the standard library,
• for UNIX the fcntl module in the standard library,
• the flufl.lock 3rd party library.

Installation#

filelock is available via PyPI, so you can pip install it:

python -m pip install filelock

Tutorial#

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: with open(file_path, "a") as f: f.write("Hello there!") lock.acquire() try: with open(file_path, "a") as f: f.write("General Kenobi!") finally: lock.release() @lock def decorated(): print("You're a decorated Jedi!") decorated() 

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): with open(file_path, "a") as f: f.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: with open(file_path, "a") as f: f.write("I hate it when he does that.") def cite2(): with lock: with open(file_path, "a") as f: f.write("You don't want to sell me death sticks.") # The lock is acquired here. with lock: cite1() cite2() # And released here. 

Logging#

All log messages by this library are made using the DEBUG_ level , under the filelock name. On how to control displaying/hiding that please consult the logging documentation of the standard library. E.g. to hide these messages you can use:

logging.getLogger("filelock").setLevel(logging.INFO) 

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 platform 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.

Asyncio support#

This library currently does not support asyncio. We’d recommend adding an asyncio variant though if someone can make a pull request for it, see here.

FileLocks and threads#

By default the FileLock internally uses threading.local to ensure that the lock is thread-local. If you have a use case where you’d like an instance of FileLock to be shared across threads, you can set the thread_local parameter to False when creating a lock. For example:

lock = FileLock("test.lock", thread_local=False) # lock will be re-entrant across threads # The same behavior would also work with other instances of BaseFileLock like SoftFileLock: soft_lock = SoftFileLock("soft_test.lock", thread_local=False) # soft_lock will be re-entrant across threads. 

Behavior where FileLock is thread-local started in version 3.11.0. Previous versions, were not thread-local by default.

Note: If disabling thread-local, be sure to remember that locks are re-entrant: You will be able to acquire the same lock multiple times across multiple threads.

Contributions and issues#

Contributions are always welcome, please make sure they pass all tests before creating a pull request. This module is hosted on GitHub. If you have any questions or suggestions, don’t hesitate to open a new issue 😊. There’s no bad question, just a missed opportunity to learn more.

Источник