Python: What is the asyncio.run_until_complete vs asyncio.run?

asyncio.run is the modern way to start an event loop. run_until_complete is lower-level.

1import asyncio
2
3async def main():
4    await asyncio.sleep(1)
5    return "Done"
6
7# Modern (Python 3.7+) — recommended
8result = asyncio.run(main())
9print(result)  # "Done"
10
11# Legacy — manual loop management
12loop = asyncio.get_event_loop()
13task = loop.create_task(main())
14loop.run_until_complete(task)
15result = task.result()
16loop.close()  # Don't forget!

Key differences:

• run creates a new loop, runs, then closes it.
• run_until_complete uses existing loop.
• run handles signal registration.
• run sets running loop context.

When to use run_until_complete:

• Integrating with existing event loops.
• Testing async code.
• When you need loop control.