Concurrent dowload in python

download.py

import asyncio
from aiohttp import ClientSession

CONCURRENT_DOWNLOADS = 16

semaphore = asyncio.Semaphore(CONCURRENT_DOWNLOADS)

def limit_concurrent(f):
    async def wrapper(*args, **kwargs):
        async with semaphore:
            return await f(*args, **kwargs)
    return wrapper

@limit_concurrent
async def download(session: ClientSession, url: str, filename: str = None):
    if not filename:
        filename = url.split('/')[-1]
    async with session.get(url, ) as res:
        with open(filename, "wb") as f:
            async for chunk, _ in res.content.iter_chunks():
                f.write(chunk)

async def main(download_list):
    async with ClientSession() as session:
        await asyncio.gather(*[download(session, i) for i in download_list])

loop = asyncio.get_event_loop()
loop.run_until_complete(main())