asyncio Concurrency Limiter (Semaphore)

import asyncio
import aiohttp

async def fetch(session, sem, url):
    async with sem:               # blocks if N tasks already inside
        async with session.get(url) as r:
            return await r.text()

async def fetch_many(urls, limit=10):
    sem = asyncio.Semaphore(limit)
    async with aiohttp.ClientSession() as session:
        return await asyncio.gather(*(fetch(session, sem, u) for u in urls))

# 1000 URLs, but never more than 10 in flight at once
urls = [f"https://api.example.com/items/{i}" for i in range(1000)]
results = asyncio.run(fetch_many(urls, limit=10))