How to use the sniffio.AsyncLibraryNotFoundError function in sniffio

The current thread must not be already running an event loop.

    :param func: a coroutine function
    :param args: positional arguments to ``func``
    :param backend: name of the asynchronous event loop implementation – one of ``asyncio``,
        ``curio`` and ``trio``
    :param backend_options: keyword arguments to call the backend ``run()`` implementation with
    :return: the return value of the coroutine function
    :raises RuntimeError: if an asynchronous event loop is already running in this thread
    :raises LookupError: if the named backend is not found

    """
    try:
        asynclib_name = sniffio.current_async_library()
    except sniffio.AsyncLibraryNotFoundError:
        pass
    else:
        raise RuntimeError(f'Already running {asynclib_name} in this thread')

    try:
        asynclib = import_module(f'{__name__}._backends._{backend}')
    except ImportError as exc:
        raise LookupError(f'No such backend: {backend}') from exc

    token = None
    if sniffio.current_async_library_cvar.get(None) is None:
        # Since we're in control of the event loop, we can cache the name of the async library
        token = sniffio.current_async_library_cvar.set(backend)

    try:
        backend_options = backend_options or {}