Concurrent I/O with Python's asyncio and async/await

This tutorial walks through Python's asyncio library by building a market data service that fetches prices from three independent REST APIs concurrently, enforces per-source deadlines, and writes a consolidated snapshot to disk. It covers the event loop and concurrency vs parallelism, async def and await, asyncio.run, asyncio.gather, asyncio.create_task, asyncio.timeout, asyncio.sleep as a stand-in for real network I/O, and non-blocking file writes with aiofiles.