semtest.py

#!/usr/bin/python3

import asyncio

async def doitem(n, sem):
    try:
        print('foo', n)
        await asyncio.sleep(1)
        print('bar', n)
    finally:
        sem.release()
    

async def run():
    sem = asyncio.Semaphore(5)
    for n in range(40):
        await sem.acquire()
        asyncio.create_task(doitem(n, sem))
        
loop = asyncio.get_event_loop()
task = loop.create_task(run())
loop.run_until_complete(task)