AttributeError: module 'asyncio' has no attribute 'create_task'

The create_task top-level function was added in Python 3.7, and you are using Python 3.6. Prior to 3.7, create_task was only available as a method on the event loop, so you can invoke it like that:

async def main():
    loop = asyncio.get_event_loop()
    task1 = loop.create_task(async_say(4, 'hello'))
    task2 = loop.create_task(async_say(6, 'world'))
    # ...
    await task1
    await task2

That works in both 3.6 and 3.7, as well as in earlier versions. asyncio.ensure_future will work as well, but when you know you're dealing with a coroutine, create_task is more explicit and is the preferred option.