# uvloop — Ultra-Fast asyncio Event Loop for Python

> A drop-in replacement for the default asyncio event loop, built on libuv, that makes Python async networking significantly faster.

## Install

Save as a script file and run:

# uvloop — Ultra-Fast asyncio Event Loop for Python

## Quick Use
```bash
pip install uvloop
```
```python
import asyncio
import uvloop

asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())

async def main():
    # your async code runs on uvloop now
    await asyncio.sleep(1)

asyncio.run(main())
```

## Introduction
uvloop is a fast, drop-in replacement for the built-in asyncio event loop in Python. It is implemented in Cython and wraps libuv, the same high-performance I/O library that powers Node.js. Switching to uvloop typically requires only two lines of code and can double or triple the throughput of asyncio-based applications.

## What uvloop Does
- Replaces the default asyncio event loop with a libuv-backed implementation
- Accelerates TCP, UDP, and Unix socket operations for async Python code
- Provides full compatibility with the standard asyncio API
- Improves performance of frameworks like aiohttp, Sanic, and FastAPI
- Supports DNS resolution, subprocess management, and signal handling

## Architecture Overview
uvloop is written in Cython and compiles to a C extension module. It wraps libuv handles and requests to implement the asyncio event loop interface. Socket I/O, timers, signal watchers, and child process management all delegate to libuv's non-blocking, cross-platform primitives. Because it follows the asyncio abstract base class contract, existing coroutines and libraries work without modification.

## Self-Hosting & Configuration
- Install with `pip install uvloop` (requires Python 3.8+)
- Activate globally with `asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())`
- Or use `uvloop.install()` as a shortcut in Python 3.12+
- No configuration files are needed; it is a runtime swap
- Works on Linux and macOS (Windows is not supported by libuv's full feature set in this context)

## Key Features
- Two to four times faster than the default asyncio loop on network benchmarks
- Zero API changes required for existing asyncio code
- Built on libuv, a proven C library with years of production use in Node.js
- Handles millions of connections efficiently with low memory overhead
- Used by Uvicorn, the default ASGI server for FastAPI and Starlette

## Comparison with Similar Tools
- **asyncio (default loop)** — Standard library implementation; uvloop is a faster drop-in alternative
- **Trio** — Alternative async library with structured concurrency; uvloop stays within the asyncio ecosystem
- **curio** — Minimal async kernel; uvloop targets the standard asyncio interface for broader compatibility
- **libuv (raw)** — C library for async I/O; uvloop wraps it and exposes it through Python's asyncio API

## FAQ
**Q: Does uvloop work on Windows?**
A: No. libuv on Windows uses IOCP which has different semantics. uvloop officially supports Linux and macOS.

**Q: Will my existing asyncio code break?**
A: No. uvloop implements the full asyncio event loop interface. Existing coroutines, tasks, and libraries work without changes.

**Q: How do I use uvloop with Uvicorn?**
A: Uvicorn uses uvloop by default when it is installed. Just `pip install uvloop` and Uvicorn will auto-detect it.

**Q: Is there a performance cost to using Cython?**
A: The Cython compilation step happens at package build time. At runtime, uvloop executes as native C code with no interpretation overhead.

## Sources
- https://github.com/MagicStack/uvloop
- https://uvloop.readthedocs.io

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Author: Script Depot