Can I use the same lock on multiple threads if they do not access the same variable?

Imagine I have two threads, each modifying a different variable. Can I pass the same lock object to them, or shall I use two separate locks? In general, when shall I use multiple locks?

Here is a toy example:

from threading import Thread, Lock
from time import sleep


def task(lock, var):
    with lock:
        var = 1
    sleep(5)


lock = Lock()

var1 = []
var2 = []

Thread(target=task, args=(lock, var1)).start()
Thread(target=task, args=(lock, var2)).start()

or is it better

lock1 = Lock()
lock2 = Lock()

var1 = []
var2 = []

Thread(target=task, args=(lock1, var1)).start()
Thread(target=task, args=(lock2, var2)).start()

>Solution :

Only one thread can hold a lock at a time, and a lock is used to provide mutually-exclusive access to a piece of data (or variable).

Based on your example, where each thread accesses separate variables, you want two separate locks—one per variable. Note that if only one thread accesses a variable, though, you do not need to use a lock for it.

If you were to only use one lock, only one thread would be able to perform "work" at a time—even though their work is completely independent.