async loop

looping.py

import asyncio
import time

sema = asyncio.Semaphore(value=5)


async def worker():
    async with sema:
        print("Start")
        await asyncio.sleep(3)
        print("Finish")


async def add():
    while True:
        await asyncio.sleep(0)
        async with sema:
            asyncio.ensure_future(worker())


async def main():
    asyncio.ensure_future(add())


loop = asyncio.get_event_loop()
asyncio.ensure_future(main())
loop.run_forever()