17. AsyncIO & Concurrency

Sync vs Async

• Sync (Blocking): You call a function, the world stops until it returns.
• Async (Non-Blocking): You call a function, it gives you a "Promise" (Future), and you can do other work while waiting.

The Event Loop

Python has a loop that watches for "awaitable" tasks.

python
import asyncio

async def fetch_data():
    print("Start fetching")
    await asyncio.sleep(1) # Simulates I/O
    print("Done fetching")
    return {"data": 1}

async def main():
    # Run concurrently
    task1 = asyncio.create_task(fetch_data())
    task2 = asyncio.create_task(fetch_data())
    
    await task1
    await task2

asyncio.run(main())