useless-with-lock (PLW2101)

Derived from the Pylint linter.

What it does

Checks for lock objects that are created and immediately discarded in with statements.

Creating a lock (via threading.Lock or similar) in a with statement has no effect, as locks are only relevant when shared between threads.

Instead, assign the lock to a variable outside the with statement, and share that variable between threads.

import threading

counter = 0


def increment():
    global counter

    with threading.Lock():
        counter += 1

Use instead:

import threading

counter = 0
lock = threading.Lock()


def increment():
    global counter

    with lock:
        counter += 1