async getitem with futures

example.py

import asyncio


class MyAsyncDict:

    async def async_getitem(self, fut, key):
        try:
            await asyncio.sleep(0.5)
            raise RuntimeError('oops')
        except Exception as e:
            fut.set_exception(e)
        else:
            fut.set_result(1)

    def __getitem__(self, key):
        loop = asyncio.get_event_loop()
        fut = loop.create_future()
        loop.create_task(self.async_getitem(fut, key))
        return fut


async def myfunc():
    a = MyAsyncDict()
    print(await a['x'])


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    try:
        loop.run_until_complete(myfunc())
    finally:
        loop.close()