How to get the 'old' value of an attribute?

[MizterB]

I would like to compare the new and old values of an attribute when it changes. Specifically, I'd like to compare the current and previous brightness of a light when I detect the brightness attribute changing in a @state_trigger.

When I create a @state_trigger for an entity attribute, I do not have access to the 'old' value of that attribute inside the function. I understand that the domain.name.old.attr form is available inside the decorator's expression, but that does not appear to carry into the function itself. Instead, the value and old_value arguments always refer back to the entity state, not the entity attribute referenced in the trigger.

Is it possible to make this data available?

[craigbarratt]

You are correct that the domain.name.old.attr form only works in trigger expressions.

However, inside the function, old_value.attr should allow you to get the attributes of the prior entity state.

[MizterB]

Unfortunately, that's not the behavior I'm seeing with this code:

@state_trigger("light.upstairs_hall_1_1_upstairs_hall_ceiling_motion_dimmer.brightness")
def jasco_motiondimmer_state(value=None, old_value=None):
    result = {}
    if value.brightness > 0:
        result["button_label"] = "up"
    elif value.brightness == 0:
        result["button_label"] = "down"
    log.debug(result)

When triggered, it throws

AttributeError: 'StateVal' object has no attribute 'brightness'

[craigbarratt]

Since your state trigger is the attribute light.upstairs_hall_1_1_upstairs_hall_ceiling_motion_dimmer.brightness, I believe value and old_value are the attribute value, not the entity (just based on quick inspection of the code; I haven't tested this).

Assuming my statement is correct, there are two different fixes. Either change your trigger to:

@state_trigger("light.upstairs_hall_1_1_upstairs_hall_ceiling_motion_dimmer")

or change your function to just use value and old_value instead of value.brightness etc.

[MizterB]

That's what I assumed, but it wasn't the behavior I was seeing - hence the issue. I was triggering on the attribute, but the values reflected the entity 'state' value, not the 'attribute' one.

[MizterB]

Just retested to make sure...

@state_trigger("light.upstairs_hall_1_1_upstairs_hall_ceiling_motion_dimmer.brightness")
def jasco_motiondimmer_state(value=None, old_value=None):
    log.debug(f"value: {value}, old_value: {old_value}")

returns state, not attribute

value: on, old_value: off