Python, asyncio: decorator in class to simplify loop syntax

Lets consider the following example of a class containing an asyncio loop and an async coroutine:

import asyncio

class Async:
    def __init__(self):
        self.loop=asyncio.get_event_loop()

    async def function(self, word):
        print(word)
        await asyncio.sleep(1.0)

a=Async()
a.loop.run_until_complete(a.function("hello_world"))

This does work.
I would like to create a decorator so that i can simplify the syntax of the code calling function to

a.function("hello_world")

I tried the following:

class Async:
    def __init__(self):
        self.loop=asyncio.get_event_loop()

    def async_loop(f):
        def decorated(*args, **kwargs):
            self.loop.run_until_complete(f(*args, **kwargs))

    @async_loop
    async def function(self, word):
        print(word)
        await asyncio.sleep(1.0)

a=Async()
a.function("hello_world")

At that point i receive the error: 'NoneType' object is not callable. - I also tried to have the decorator function outside of the class, but i got the same error. I'm not sure whether the decorator function best stands inside the claass (as a method) or outside. I'm quite new to python so Asyncio, decorator, and decorators in classes are still quite confusing for me. Any good soul would have an idea how to do that code correctly?