python-asyncio

## Quick Reference

| Function | Purpose | Code |
|----------|---------|------|
| `asyncio.run()` | Entry point | `asyncio.run(main())` |
| `asyncio.gather()` | Concurrent tasks | `await asyncio.gather(*tasks)` |
| `asyncio.create_task()` | Fire-and-await | `task = asyncio.create_task(coro)` |
| `asyncio.TaskGroup()` | Structured concurrency | `async with asyncio.TaskGroup() as tg:` |
| `asyncio.Semaphore()` | Rate limiting | `async with semaphore:` |
| `asyncio.timeout()` | Timeout (3.11+) | `async with asyncio.timeout(5.0):` |

| Pattern | Sequential | Concurrent |
|---------|------------|------------|
| Execution | `await a(); await b()` | `await gather(a(), b())` |
| Time | Sum of durations | Max of durations |

| Library | Use Case |
|---------|----------|
| `aiohttp` | HTTP client (most popular) |
| `httpx` | HTTP (sync + async) |
| `asyncpg` | PostgreSQL |
| `uvloop` | 2-4x faster event loop |

## When to Use This Skill

Use for **async/concurrent programming**:
- Network requests (HTTP, WebSockets)
- Database queries
- File I/O operations
- Multiple concurrent I/O operations
- FastAPI/Starlette async endpoints

**Related skills:**
- For FastAPI: see `python-fastapi`
- For type hints: see `python-type-hints`
- For gotchas: see `python-gotchas`

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# Python Asyncio Complete Guide

## Overview

Asyncio is Python's built-in framework for writing concurrent code using async/await syntax. It's ideal for I/O-bound operations like network requests, file I/O, and database queries.

## When to Use Asyncio

### Good Use Cases
- Network requests (HTTP clients, WebSockets)
- Database queries
- File I/O operations
- Web servers (FastAPI, Starlette)
- Message queues
- Multiple concurrent I/O operations

### When NOT to Use
- CPU-bound tasks (use multiprocessing instead)
- Simple sequential scripts
- Legacy codebases without async support

## Core Concepts

### Basic Async/Await

```python
import asyncio

# Async function (coroutine)
async def fetch_data(url: str) -> dict