asynctopo.py

import asyncio
from graphlib import TopologicalSorter

graph = {
    "A": ["B", "C"],
    "B": ["D"],
    "C": ["D"],
    "D": ["E"],
}


async def runner(node: str, sorter: TopologicalSorter):
    print(f"processing node {node}")
    sorter.done(node)


async def main():
    sorter = TopologicalSorter(graph)

    sorter.prepare()

    while sorter.is_active():
        node_group = sorter.get_ready()

        if not node_group:
            await asyncio.sleep(0.25)
        else:
            tasks = set()
            for node in node_group:
                task = asyncio.create_task(runner(node, sorter))
                tasks.add(task)
                task.add_done_callback(tasks.discard)


if __name__ == "__main__":
    asyncio.run(main())