What is the `threading` module?

Question

Accepted Answer

**threading** — run code concurrently using OS threads.

```python
import threading
import time

def worker(name, delay):
    for i in range(3):
        time.sleep(delay)
        print(f"{name}: {i}")

# Create threads
t1 = threading.Thread(target=worker, args=("A", 0.5))
t2 = threading.Thread(target=worker, args=("B", 0.3))

# Start and join
t1.start()
t2.start()
t1.join()  # Wait for t1
t2.join()  # Wait for t2

# Lock for shared resources
counter = 0
lock = threading.Lock()

def increment():
    global counter
    with lock:
        counter += 1

# Thread pool
from concurrent.futures import ThreadPoolExecutor

with ThreadPoolExecutor(max_workers=4) as executor:
    futures = [executor.submit(worker, f"Thread-{i}", 0.1) for i in range(4)]
```

**GIL consideration:**
- Threads don't help with CPU-bound work.
- Good for I/O-bound work (network, file I/O).

Python: What is the `threading` module?