How to modify a single field of an object contained in a Variable?

[gmulders]

I'm trying to do the following:

• read the state from a light from someplace (state includes on/off, brightness, color)
• store the state in a Variable light_state
• show an on/off switch in the ui
• modify the on/off state in the light_state variable
• update the source from the light_state variable (to actually turn the light on or off)

The last step needs the entire light_state to work.

In my attempt I created an extra bool variable light_on that is connected with the light_state and can be shown as a switch. However I'm not sure how to update the light_state when the light_on gets updated.

[gmulders]

To answer my own question; I believe that the tuple field access is for this: https://smarthomeconnect.readthedocs.io/en/latest/variables_expressions.html#tuple-field-access

[mhthies]

Thanks for checking out SHC and for your question! 🙂

So, if I understand correctly, you want to keep multiple properties of a single light in a single Variable. That's not strictly necessary; in my personal SHC projects, I just created multiple Variables for lights which have an on/off value and e.g. a dimmer percentage value.

If you still want to do that, you're right with your own answer: You can create a typed NamedTuple and use it as the Variable's value type. Than you can use the Variable.field() method to retrieve connectable objects representing the individual fields of that tuple:

import typing
import shc
import shc.web
import shc.web.widgets


class MySpecialLightbulb(typing.NamedTuple):
    on_off: bool
    brightness: shc.datatypes.RangeFloat1
    color: shc.datatypes.RGBUInt8


light_state = shc.Variable(MySpecialLightbulb, "light_state")\
    .connect(my_special_light_interface.light_state_connector())  # or however you get the connectable object for your light


web_server = shc.web.WebServer('localhost', 8080, index_name='index')
page = web_server.page('index', 'Home')
page.add_item(shc.web.widgets.Switch("My light", color="yellow")
              .connect(light_state.field("on_off")))

The interesting bit w.r.t. to your question is the last line of that snippet: There, the Switch UI widget is connected to the 'on_off' field of the light_state variable.

Note, that in this configuration, upon every change of the on_off value, the full MySpecialLightbulb value is published/written to the other interface (which I called 'my_special_light_interface' above). The other fields ('brightness' and 'color') are set to the latest values that have been written to the Variable.

Further note, that this will only work, once the Variable itself is initialized with a complete MySpecialLightbulb value. You might want to use an initial_value in the construction of the Variable to ensure this at application startup.