What are semaphores in Python and can you provide examples?

What are semaphores in Python and can you provide examples?

Semaphores are synchronization primitives that control access to a shared resource in concurrent programming. In Python, you can use the threading module to implement semaphores. Would you like to see a code example?

Yes, please show me a simple example of using a semaphore.

Here's a basic example:

import threading
import time

# Create a semaphore with a limit of 2
semaphore = threading.Semaphore(2)

def worker(num):
    print(f'Worker {num} is waiting to enter...')
    semaphore.acquire()
    print(f'Worker {num} has entered!')
    time.sleep(2)  # Simulate work
    print(f'Worker {num} is leaving...')
    semaphore.release()

# Create multiple threads
threads = []
for i in range(5):
    t = threading.Thread(target=worker, args=(i,))
    threads.append(t)
    t.start()

# Wait for all threads to complete
for t in threads:
    t.join()

This code creates a semaphore that allows up to 2 workers to access a resource at the same time.

What happens if more than 2 workers try to enter?

If more than 2 workers try to enter, they will be blocked until one of the currently active workers releases the semaphore. This ensures that only 2 workers can access the shared resource simultaneously.