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Inside the Asyncio Event Loop

Asyncio Core

Event Loop Fundamentals

The event loop drives asyncio. Understand how it schedules tasks, handles callbacks, and wakes up on I/O readiness.

LifecycleIntegrate blocking code

Lifecycle​

import asyncio

async def main():
    await asyncio.sleep(1)

asyncio.run(main())
  • asyncio.run creates an event loop, runs the coroutine, then closes the loop.
  • Inside the loop, tasks are awaited; when they yield control, the loop schedules other awaiting tasks.
  • Under the hood, the loop relies on selectors (epoll/kqueue/IOCP) for efficient I/O.

Integrating blocking code​

  • Use await loop.run_in_executor(None, blocking_func) or asyncio.to_thread to run blocking functions without freezing the loop.
  • Use asyncio.create_task to schedule background tasks; remember to await or handle their result to avoid swallowing errors.

Next up in your learning path

async/await

Write coroutines that cooperate with the loop.

Hands-on

aiohttp

Build HTTP clients/servers on top of asyncio.

Practical

threading vs async

Review when to choose each model.

Comparison