trio

Trio is a Python library for async concurrency built on one big idea: structured concurrency. Tasks live inside "nurseries" that own them, so when the block exits, every task it started is finished or cancelled. No orphaned coroutines, no leaked tasks. If you write servers, scrapers, or anything juggling lots of network calls at once, this makes correct concurrency much harder to get wrong.

Install is trivial, `pip install trio`, pure Python, no compiler. The real cost is in your head. Structured concurrency is a different model than asyncio, and adopting it means learning to think in nurseries and cancel scopes. It's worth it, but it isn't free.

For a new project where getting concurrency right matters, Trio is the clearer foundation, and its ideas were good enough that Python's own asyncio borrowed them as TaskGroups. The catch is the ecosystem. Asyncio is the default, so most third-party async libraries target it, not Trio. You'll lean on the trio-asyncio bridge or Trio-native packages, and sometimes you'll hit friction the asyncio crowd never sees. Pick Trio for correctness, and know you're off the main road.