Python Async & Concurrency

When to use this skill

• Writing high-concurrency I/O bound applications (FastAPI, bots, scrapers).
• Using

  asyncio

  ,

  aiohttp

  , or

  httpx

  .
• Managing background tasks or task queues.

1. Asyncio Basics

• Entry Point: Use

  asyncio.run(main())

  for the entry point.
• TaskGroups: Use

  async with asyncio.TaskGroup() as tg

  (Python 3.11+) instead of

  gather()

  for better error handling/cancellation.
• Blocking Code: Run blocking (CPU-bound) code in

  await asyncio.to_thread(...)

  .

2. HTTP Clients

• HTPX/AIOHTTP: Use

  httpx.AsyncClient

  or

  aiohttp.ClientSession

  as a context manager.
• Singleton: Reuse the client session across requests; do not create a new one per request.

3. Pitfalls

• Sync in Async: Never call blocking sync functions (requests, time.sleep) inside async functions.
• Fire and Forget: Avoid unreferenced background tasks; keep a reference to prevent garbage collection (or use

  TaskGroup

  ).