Proof that concurrent.future's executor.map returns values in order

concurrent_executor_map_order_proof.py

import time
import random
import concurrent.futures

e = concurrent.futures.ThreadPoolExecutor(4)
s = range(10)

def sleep_and_return(i):
    time.sleep(random.randint(3,7))
    return i

for i in e.map(sleep_and_return, s):
    print(i)