futures.py

from concurrent.futures import ThreadPoolExecutor, as_completed

def get_something(x):
    return x

MAX_WORKERS = 8
iterable = range(20)
with ThreadPoolExecutor(max_workers=MAX_WORKERS) as pool:
    futures = [pool.submit(get_something, x) for x in iterable]
    for future in as_completed(futures):
        result = future.result()