.. py:currentmodule:: sdbus

D-Bus allows signals to not carry any data. Such signals have the type signature of "". (empty string)

To emit such signals the :py:meth:`emit <DbusSignalAsync.emit>` must be explicitly called with None.

Example of an empty signal:

from asyncio import new_event_loop
from sdbus import DbusInterfaceCommonAsync, dbus_signal_async


class ExampleInterface(
    DbusInterfaceCommonAsync,
    interface_name="org.example.signal"
):

    @dbus_signal_async("")
    def name_invalidated(self) -> None:
        raise NotImplementedError


test_object = ExampleInterface()


async def emit_empty_signal() -> None:
    test_object.export_to_dbus("/")

    test_object.name_invalidated.emit(None)


loop = new_event_loop()
loop.run_until_complete(emit_empty_signal())