# Trio — Structured Concurrency for Python

> Trio is a Python async/await library that makes concurrent I/O programming easy, correct, and pleasant by enforcing structured concurrency where every task has a well-defined lifetime and clean error propagation.

## Install

Save in your project root:

# Trio — Structured Concurrency for Python

## Quick Use
```bash
pip install trio

import trio

async def fetch(url):
    print(f"Fetching {url}")
    await trio.sleep(1)
    print(f"Done: {url}")

async def main():
    async with trio.open_nursery() as nursery:
        nursery.start_soon(fetch, "https://example.com/a")
        nursery.start_soon(fetch, "https://example.com/b")

trio.run(main)
```

## Introduction
Trio rethinks Python's async concurrency around the principle of structured concurrency: every concurrent task belongs to a nursery that manages its lifetime. This eliminates orphaned tasks, guarantees cleanup, and makes error handling predictable in ways that raw asyncio cannot.

## What Trio Does
- Runs concurrent async tasks within nurseries that enforce lifetime boundaries
- Guarantees that exceptions propagate cleanly and all child tasks finish before the parent continues
- Provides cancellation scopes with deadlines and cancel tokens
- Offers high-level networking, file I/O, and synchronization primitives
- Eliminates common async bugs like fire-and-forget tasks and swallowed exceptions

## Architecture Overview
Trio uses a single-threaded event loop with cooperative scheduling. The nursery abstraction forms a task tree where each nursery awaits all its child tasks before returning. Cancellation flows downward through the tree via cancel scopes. The I/O layer uses platform-native APIs (epoll, kqueue, IOCP) through a thin abstraction.

## Self-Hosting & Configuration
- Install via pip; supports Python 3.8+
- No configuration files; use `trio.run()` as the entry point
- Add trio-compatible libraries (httpx, asks, trio-websocket) for network clients
- Use `trio.testing` module for deterministic async test helpers
- Combine with Hypercorn or Uvicorn (via anyio) for web server deployment

## Key Features
- Nurseries guarantee no orphaned tasks and proper cleanup on failure
- Cancel scopes with deadlines provide structured timeouts
- Checkpoints are explicit, making it clear where context switches occur
- Rich debugging support with task tree introspection
- Designed for correctness first, then performance

## Comparison with Similar Tools
- **asyncio** — stdlib but allows fire-and-forget tasks and has complex cancellation; Trio enforces structure
- **anyio** — compatibility layer that runs on both asyncio and Trio backends
- **Twisted** — callback-based (with deferred); Trio uses native async/await
- **Curio** — similar structured approach but less actively maintained; Trio has a larger ecosystem

## FAQ
**Q: Can I use Trio with existing asyncio libraries?**
A: Use the `trio-asyncio` bridge or choose libraries built on `anyio` which supports both backends natively.

**Q: What is structured concurrency?**
A: A paradigm where concurrent tasks are scoped to a block (nursery). When the block exits, all tasks inside it have completed or been cancelled. No task can outlive its parent scope.

**Q: Is Trio production-ready?**
A: Yes. Trio is used in production systems and has a stable API. Libraries like httpx and Starlette support it via anyio.

**Q: How does Trio handle timeouts?**
A: Wrap code in `with trio.move_on_after(seconds):` or `with trio.fail_after(seconds):` to apply cancel-scope deadlines that propagate to all child tasks.

## Sources
- https://github.com/python-trio/trio
- https://trio.readthedocs.io

---
Source: https://tokrepo.com/en/workflows/asset-fcbc710d
Author: AI Open Source