Experimenting with run_secretly_sync_async_fn

secretly_sync.py

import trio


class SyncBackend:
    def return_2(self):
        return 2


class AsyncBackend:
    async def return_2(self):
        return 2


async def work(backend):
    print(await backend.return_2())


# async usage, works as expected
trio.run(work, AsyncBackend())

# adapted from https://github.com/python-trio/hip/issues/1#issuecomment-322028457
def run_secretly_sync_async_fn(async_fn, *args, **kwargs):
    coro = async_fn(*args, **kwargs)
    try:
        coro.send(None)
    except StopIteration as exc:
        return exc.value
    else:
        raise RuntimeError("you lied, this async function is not secretly synchronous")


# sync usage, fails with TypeError: object int can't be used in 'await' expression
run_secretly_sync_async_fn(work, backend=SyncBackend())