async — Advanced Examples

import asyncio

class AsyncTimer:
    def __init__(self, label):
        self.label = label

    async def __aenter__(self):
        print(f"  [{self.label}] Starting")
        self.start = asyncio.get_event_loop().time()
        return self

    async def __aexit__(self, *args):
        elapsed = asyncio.get_event_loop().time() - self.start
        print(f"  [{self.label}] Done ({elapsed:.4f}s)")

async def main():
    async with AsyncTimer("task"):
        await asyncio.sleep(0.01)

    # Semaphore for concurrency limiting
    sem = asyncio.Semaphore(2)
    async def limited_task(n):
        async with sem:
            print(f"  Task {n} running")
            await asyncio.sleep(0.01)

    await asyncio.gather(*[limited_task(i) for i in range(5)])

asyncio.run(main())