Stop Hot Loops: What to Do When Coroutines Never Await

If a coroutine in your loop never calls await, it can create a hot loop that starves your event loop. Catch it by...

September 05, 2025

In partnership with

New at hackr.io

This week we’re looking at one of the easiest mistakes to make in async Python: missing awaits. It’s subtle, but the fix is straightforward once you know what to look for.

Partner Message

9 Surprising Amazon Prime Features You’re Missing Out On

Amazon Prime isn’t just about free shipping and streaming – it’s loaded with perks you might not even know exist. From exclusive discounts to free photo storage, these 9 hidden features can take your Prime experience to the next level. Don’t miss out on the benefits that can help you save more, shop smarter, and enjoy even more from your membership. It only takes a few clicks to unlock these powerful perks. You’re already paying for it – now make sure you’re getting everything you deserve.

The Scoop

Why This Happens

Asyncio coroutines rely on await to hand control back to the event loop. If you forget it, the loop never releases, creating a hot loop that spins uncontrollably.

What To Do

  1. Add await asyncio.sleep(0) inside long-running loops to yield.

  2. Double-check that every async call is properly awaited.

  3. Use linting tools and type checkers to catch missed awaits before runtime.

# Bad: Hot loop burns CPU
async def worker():
    while True:
        do_work()  # No await here, loop never yields

To fix this, try:

# Fixed: Yields control back
async def worker():
    while True:
        do_work()
        await asyncio.sleep(0)  # or another async call

Partner Message

Marketing ideas for marketers who hate boring

The best marketing ideas come from marketers who live it.

That’s what this newsletter delivers.

The Marketing Millennials is a look inside what’s working right now for other marketers. No theory. No fluff. Just real insights and ideas you can actually use—from marketers who’ve been there, done that, and are sharing the playbook.

Every newsletter is written by Daniel Murray, a marketer obsessed with what goes into great marketing. Expect fresh takes, hot topics, and the kind of stuff you’ll want to steal for your next campaign.

Because marketing shouldn’t feel like guesswork. And you shouldn’t have to dig for the good stuff.

Full Python Course

And test your skills in real time with the free online Python editor.

Get full access to Python with Dr. Johns when you sign up for Hackr Premium.

“Robert is a great teacher! The material is concise and easy to follow along with.”

Dovi
Skills

Asyncio Debug Mode

Python has a built-in debug mode for asyncio. It can warn you about tasks that were never awaited and help track down tight loops that chew up resources.

Best Practices for Async Loops

  • Avoid while True without a clear await path.

  • Consider using asyncio.create_task for background work.

  • Profile your event loop if you see unexplained CPU spikes.

Modern async programming is powerful, but a single missed await can cost you hours of debugging. Add a few checks and safeguards now, and your coroutines will behave.

That’s it for today.

Thanks for being part of the Hackr.io community. Keep building. Keep pushing your skills.

The Hackr.io Team

P.S.

New here? Browse Python projects to build real-world skills you can bring to any industry.