What is the `concurrent.futures` module?

Question

Accepted Answer

**concurrent.futures** — high-level interface for async execution.

```python
from concurrent.futures import ThreadPoolExecutor, ProcessPoolExecutor, as_completed
import time

def fetch(url):
    time.sleep(1)  # Simulate network
    return f"Data from {url}"

# ThreadPoolExecutor
urls = ["url1", "url2", "url3", "url4"]

with ThreadPoolExecutor(max_workers=4) as executor:
    # Submit and get futures
    futures = {executor.submit(fetch, url): url for url in urls}
    
    # Process as completed
    for future in as_completed(futures):
        url = futures[future]
        try:
            result = future.result()
            print(f"{url}: {result}")
        except Exception as e:
            print(f"{url} failed: {e}")

# ProcessPoolExecutor for CPU-bound
with ProcessPoolExecutor() as executor:
    results = list(executor.map(cpu_bound, data_chunks))
```

**Key features:**
- Future objects for result handling.
- as_completed() for ordered results.
- Submit/map patterns.

Python: What is the `concurrent.futures` module?