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How to implement a dynamic attribute from signal
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:ref:`how-to-event-driven` describes how to use :class:`.attribute_from_signal` to implement an event driven Tango device with a static set of attributes using a static set of signals.  The signal bus mechanism also supports a more dynamically generated signal names and working with dynamic attributes.  When using dynamic signal names, we cannot use the signal data descriptors and must use :meth:`.BusProtocol.emit` ourselves.  Dynamic attributes can be used with signal data descriptors, provided the signal name is known statically.

For example, the following device dynamically adds an attribute using a random signal name which is updated randomly every time the :func:`!MyCmd` command is called:

.. code :: python

    class MyDevice(stb.software_bus.SignalBusMixin, stb.SKADevice):
        def init_device(self) -> None:
            super().init_device()

            self.signal = randomise_signal_name()
            self.add_attribute(
                stb.software_bus.attribute_from_signal(
                    self.signal, name="myDynAttr", dtype=int
                )
            )

    @tango.server.command
    def MyCmd(self) -> None:
        self.shared_bus.emit(self.signal, randomise_value())