Context switching from one blocking statement to other and switching back to one until the other resumes.

context_swtiching.py

import concurrent.futures as cf
import asyncio
from time import sleep


def two():
    print('two')
    sleep(4)  # blocking
    print('two again')


async def foo(loop: asyncio.AbstractEventLoop):
    print('one')
    with cf.ThreadPoolExecutor() as pool:
        future = loop.run_in_executor(pool, two)
        print('\none again')  # switches context here
        return future


loop = asyncio.get_event_loop()

asyncio.run(foo(loop))