Optional members

The decorators @dbus_method(), @dbus_property(), and @dbus_signal() are collected from the class when an interface is constructed, so the set of members is normally fixed when you write the class. A common need, though, is to write the interface once with all of its members and then expose only some of them depending on runtime configuration.

The disabled argument accepted by each decorator is evaluated when the class is built, so wrapping the class body in a factory function lets you produce variants of an interface with different optional members enabled. Passing the set of members to enable — rather than to disable — keeps any members added later opt-in:

from dbus_fast.annotations import DBusStr, DBusUInt16
from dbus_fast.service import ServiceInterface, dbus_property, PropertyAccess


def make_advertisement(enabled_properties=("Appearance", "LocalName")):
    class Advertisement(ServiceInterface):
        def __init__(self, name="org.example.Advertisement"):
            super().__init__(name)
            self._appearance = 0
            self._local_name = ""

        @dbus_property(
            PropertyAccess.READ,
            disabled="Appearance" not in enabled_properties,
        )
        def Appearance(self) -> DBusUInt16:
            return self._appearance

        @dbus_property(
            PropertyAccess.READ,
            disabled="LocalName" not in enabled_properties,
        )
        def LocalName(self) -> DBusStr:
            return self._local_name

    return Advertisement


# All properties enabled.
Advertisement = make_advertisement()
# A variant that exposes only LocalName.
MinimalAdvertisement = make_advertisement(enabled_properties=["LocalName"])

Build the class once and reuse it for every instance — there is no need to rebuild it per object.