How Python's asyncio Event Loop Works Under the Hood

Python's asyncio is commonly used through its public API, but the underlying mechanics explain why the library behaves as it does. At its core, the event loop runs a short cycle: resume a coroutine, observe what it is waiting for, and arrange to resume it once that dependency is ready. Native coroutines build on the same suspend-and-resume principle as Python generators, using send(), throw(), and close() to drive execution frames from outside. The await keyword does not block the event-loop thread; instead, it suspends the current coroutine and returns control to the scheduler, which can then run other ready tasks. A suspended coroutine consumes no CPU, which is why a single thread can manage thousands of concurrent network connections efficiently.