Asynchronous context managers

You can use the following pattern to implement context managers with asynchronous entry:

def my_coro():
    with (yield my_context_manager(x=5)) as val:
        print(f"Got val {val}")

where:

def my_context_manager(x):
    print("Initialising...")
    yield tinyio.sleep(1)
    print("Initialised")
    return make_context_manager(x)

@contextlib.contextmanager
def make_context_manager(x):
    try:
        yield x
    finally:
        print("Cleaning up")

This isn't anything fancier than just using a coroutine that returns a regular with-compatible context manager. See the source code for tinyio.Semaphore for an example of this pattern.