py-asynclisted

# Python Async Patterns Python's asyncio runs on a single thread. Like Node.js, blocking that thread stalls every coroutine waiting to run. Most asyncio bugs are either blocking calls in async context or mismanaged coroutine scheduling. ## Never block the event loop Any synchronous I/O or CPU-heavy work inside an `async` function blocks all other coroutines. ```python # Bad: requests is synchronous — blocks the event loop entirely async def fetch_user(user_id: str) -> dict: response = requests.get(f'/users/{user_id}') # blocks return response.json() # Good: use an async HTTP client import httpx async def fetch_user(user_id: str) -> dict: async with httpx.AsyncClient() as client: response = await client.get(f'/users/{user_id}') return response.json() ``` Common blocking calls to replace: | Blocking | Async alternative | |---|---| | `requests` | `httpx` (async), `aiohttp` | | `time.sleep` | `await asyncio.sleep` | | `open()` / file I/O | `aiofiles` or `asyncio.to_thread` | | `psycopg2` | `asyncpg`, `psycopg3` (async mode) | For sync code you can't replace, run it in a thread: ```python import asyncio async def process(): result = await asyncio.to_thread(blocking_cpu_work, data) return result ``` `asyncio.to_thread` (Python 3.9+) runs the function in a thread pool executor without blocking the event loop. ## Always `await` coroutines Calling a coroutine without `await` creates a coroutine object but never runs it. Python will war