How to use the uvicorn.importer.import_from_string function in uvicorn

def test_invalid_module():
    with pytest.raises(ImportFromStringError) as exc:
        import_from_string("module_does_not_exist:myattr")
    expected = 'Could not import module "module_does_not_exist".'
    assert expected in str(exc)

def test_internal_import_error():
    with pytest.raises(ImportError) as exc:
        import_from_string("tests.importer.raise_import_error:myattr")

def test_no_import_needed():
    from tempfile import TemporaryFile

    instance = import_from_string(TemporaryFile)
    assert instance == TemporaryFile

encoded_headers
            if b"server" in dict(encoded_headers)
            else [(b"server", b"uvicorn")] + encoded_headers
        )  # type: List[Tuple[bytes, bytes]]

        if isinstance(self.http, str):
            self.http_protocol_class = import_from_string(HTTP_PROTOCOLS[self.http])
        else:
            self.http_protocol_class = self.http

        if isinstance(self.ws, str):
            self.ws_protocol_class = import_from_string(WS_PROTOCOLS[self.ws])
        else:
            self.ws_protocol_class = self.ws

        self.lifespan_class = import_from_string(LIFESPAN[self.lifespan])

        try:
            self.loaded_app = import_from_string(self.app)
        except ImportFromStringError as exc:
            logger.error("Error loading ASGI app. %s" % exc)
            sys.exit(1)

        if self.interface == "auto":
            if inspect.isclass(self.loaded_app):
                use_asgi_3 = hasattr(self.loaded_app, "__await__")
            elif inspect.isfunction(self.loaded_app):
                use_asgi_3 = asyncio.iscoroutinefunction(self.loaded_app)
            else:
                call = getattr(self.loaded_app, "__call__", None)
                use_asgi_3 = asyncio.iscoroutinefunction(call)
            self.interface = "asgi3" if use_asgi_3 else "asgi2"

def setup_event_loop(self):
        loop_setup = import_from_string(LOOP_SETUPS[self.loop])
        if loop_setup is not None:
            loop_setup()