asyncio_cancel.py

import asyncio


async def A():
    try:
        await asyncio.sleep(100)
    except asyncio.CancelledError:
        print("canceled (A)")


async def B():
    try:
        await A()
    except asyncio.CancelledError:
        print("canceled (B)")
        raise
    print('will block forever and prevents C to cancels')
    await asyncio.sleep(100000)

async def C():
    try:
        await B()
    except asyncio.CancelledError:
        print("canceled (C)")
        raise

task = asyncio.ensure_future(C())

loop = asyncio.get_event_loop()
try:
    loop.run_until_complete(task)
except KeyboardInterrupt:
    task.cancel()
    try:
        loop.run_until_complete(task)
    except asyncio.CancelledError:
        pass
    print("Task is canceled:", task.cancelled())