How do i use ThreadPoolExecutor submit with a function that yields in Python?

I have the following code.

def foos(n):
    sleep(0.5)
    yield n

k = 8
futures = []
with ThreadPoolExecutor(10) as exc:
    for i in range(k):
        futures.append(exc.submit(foos, i))
    for future in as_completed(futures):
        result = future.result()
        for v in result:
            print(v)

This code currently prints sequentially with an interval of 0.5 secs. How do i concurrently pull the results?