How does Semaphore differ from Lock in asyncio?

In asyncio, Lock and Semaphore are used to control access to resources, but they differ in purpose and behavior.

• Lock is a simple locking mechanism that allows only one coroutine to access the resource at a time. If the Lock is occupied, other coroutines wait for it to be released.

• Semaphore allows limiting the number of coroutines that can access the resource simultaneously, with the limit set at creation. For example, Semaphore(3) allows three coroutines to work at the same time.

Example usage:

import asyncio

async def worker(sem, worker_id):
    async with sem:
        print(f"Worker {worker_id} started")
        await asyncio.sleep(1)
        print(f"Worker {worker_id} finished")

async def main():
    sem = asyncio.Semaphore(2)  # maximum 2 coroutines at the same time
    await asyncio.gather(*(worker(sem, i) for i in range(5)))

asyncio.run(main())

In this example, no more than two workers will run simultaneously.

Thus, Lock is a special case of a semaphore with a maximum value of 1.