Examples

This section contains a few extra examples.

Simple example

The following example shows the definition of a rectangle device, getting its width and height from other devices:

from facadevice import Facade, proxy_attribute, logical_attribute


class Rectangle(Facade):

    Width = proxy_attribute(
        property_name='WidthAttribute')

    Height = proxy_attribute(
        property_name='HeightAttribute')

    @logical_attribute(
        bind=['Width', 'Height'])
    def Area(width, height):
        return width * height

if __name__ == '__main__':
    Rectangle.run_server()

A rectangle device is configured using 2 device properties, e.g.:

• WidthAttribute: geometry/point/a/x
• HeightAttribute: geometry/point/b/y

The remote attributes are expected to push either change or periodic events.

A rectangle device exposes 3 float attributes:

• Width
• Height
• Area

Those attributes will be updated as soon as a corresponding event is received. They also pushes events, allowing other high-level devices to react to their changes.

Real-world example

A real-world example of a camera screen device used at MAX-IV:

from tango import DevState
from facadedevice import Facade, proxy_command
from facadedevice import proxy_attribute, logical_attribute, state_attribute


class CameraScreen(Facade):

    # Proxy attributes

    StatusIn = proxy_attribute(
        dtype=bool,
        property_name="StatusInAttribute")

    StatusOut = proxy_attribute(
        dtype=bool,
        property_name="StatusOutAttribute")

    # Logical attributes

    @logical_attribute(
        dtype=bool,
        bind=['StatusIn', 'StatusOut'])
    def Error(self, status_in, status_out):
        return status_in and status_out

    @logical_attribute(
        dtype=bool,
        bind=['StatusIn', 'StatusOut'])
    def Moving(self, status_in, status_out):
        return not status_in and not status_out

    # Proxy commands

    @proxy_command(
        property_name="MoveInAttribute",
        write_attribute=True)
    def MoveIn(self, subcommand):
        subcommand(1)

    @proxy_command(
        property_name="MoveOutAttribute",
        write_attribute=True)
    def MoveOut(self, subcommand):
        subcommand(1)

    # State and status

    @state_attribute(
        bind=['Error', 'Moving', 'StatusIn'])
    def state(self, error, moving, status_in):
        if error:
            return DevState.FAULT, "A conflict has been detected"
        elif moving:
            return DevState.MOVING, "The screen is moving"
        elif status_in:
            return DevState.INSERT, "The screen is inserted"
        else:
            return DevState.EXTRACT, "The screen is exctracted"


if __name__ == '__main__':
    CameraScreen.run_server()