Does python3 asyncio use a work stealing scheduler like Rust Tokio?

"Work-stealing" is a property of multi-threaded executors. Python asyncio's executor (event loop) is single-threaded, so it's by definition not work-stealing. The behavior of the asyncio event loop wrt threads is documented (among other places) in the Concurrency and Multithreading section of the documentation.

As for the algorithm used for scheduling, it's intentionally unspecified, but the stdlib implementation uses:

• a deque to store callbacks that are ready to run (those scheduled with call_soon() or create_task()) as well as those associated with file descriptors that are ready to read/write, and
• a binary heap to store callbacks scheduled for a particular time ordered by the absolute time when they're supposed to fire. This covers callbacks scheduled by loop.call_after() and loop.call_at(), but also continuation of coroutines suspended by asyncio.sleep(), which internally uses loop.call_at().

At each loop iteration the loop waits for something to happen on file descriptors associated with coroutines and sets the timeout to interrupt the sleep at the nearest time-based callback, in case nothing interesting happens before that. It proceeds to call the ready callbacks and the timeouts scheduled to run at the current or earlier time. This is repeated until the event loop is instructed to stop.