这是取消任务的示例：

import asyncio


async def some_func():
    await asyncio.sleep(2)
    print('Haha! Task keeps running!')
    await asyncio.sleep(2)

async def cancel(task):
    await asyncio.sleep(1)
    task.cancel()

async def main():
    func_task = asyncio.ensure_future(some_func())
    cancel_task = asyncio.ensure_future(cancel(func_task))
    try:
        await func_task
    except asyncio.CancelledError:
        print('Task cancelled as expected')

if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())

# Task cancelled as expected
# [Finished in 1.2s]

正常，任务已取消。如果CancelledError陷在some_func任务中不会被取消：

async def some_func():
    try:
        await asyncio.sleep(2)
    except:
        pass
    print('Haha! Task keeps running!')
    await asyncio.sleep(2)

# Haha! Task keeps running!
# [Finished in 3.2s]

可能很容易忘记我不应该在异步代码内（some_func例如，可以是第三方代码）禁止任何地方的异常，但是 应该
取消任务。反正我能做到吗？还是被忽略CancelledError意味着任务根本无法取消？