Custom sensor unavailable

[jamesball]

Hello! I am trying to create a customer sensor to calculate days until I need to change my HVAC filter. Unfortunately the newly created sensor shows as unavailable.

First, I created two Helpers to output values that will be used in my customer sensor:

input_datetime:
  air_filter_installed:
    name: Air Filter Installed
    icon: mdi:air-filter
    has_date: true
    has_time: false

input_number:
  air_filter_lifespan:
    name: Air Filter Lifespan
    initial: 90
    min: 0
    max: 365
    step: 1
    mode: box
    unit_of_measurement: days
    icon: mdi:history

Then I created the sensor:

sensor:
  - platform: template
    sensors:
      air_filter_days_remaining:
        friendly_name: "Air Filter Days Remaining"
        unique_id: "air filter timer"
        unit_of_measurement: "days"
        icon_template: 'mdi:calendar-clock'
        value_template: >-
         {%- set inst = as_timestamp(states('input_datetime.air_filter_installed')) -%}
         {%- set dif = states('input_number.air_filter_lifespan') | int * 86400 -%}
         {%- set nt = as_timestamp(states('sensor.date')) -%}
         {{ (((inst + dif) - nt) / 86400) | round(0) }}

Everything seems to work, I get no config errors and I can see the newly created entities but the custom sensor shows as unavailable.

Where am I going wrong?

Thanks,

[KSC]

@jamesball

Everything seems to work, I get no config errors and I can see the newly created entities but the custom sensor shows as unavailable.

Hi, @jamesball - have you perchance tried the template statements in the developer template tool? You can print out the actual values - specifically the values for inst, dif, nt, and then the answer. I’m not in front of a computer at the moment, but will try tomorrow.

[tom_l]

I suspect your issue is because your input_datetime is not a datetime object, it is a string. datetime object methods are unavailable unless one first converts the string via strptime. Check this in the template editor:

@jamesball

{{ as_timestamp(states('input_datetime.air_filter_installed')) }}

Then vote here:

Make typed states available for entities

In the forum and on Discord, I often see people struggle with casting states to the appropriate type for a calculation or comparison (math, date, etc.). This stems from the fact that all states are represented as strings, and any calculation/comparison of a string with a typed value will likely either result in an unexpected error, or just fail silently. Either way, it adds a barrier for new users to not only understand that states are strings, but also how to convert that string into somethin…

From the templating docs:

• as_timestamp() converts datetime object or string to UNIX timestamp.

• strptime(string, format) parses a string based on a format and returns a datetime object.

[jamesball]

I didn’t know that this tool existed - thanks for pointing it out! I found the error… I didn’t have a sensor.date entity so that is why it wouldn’t work.

I added these lines into my config file and then it worked:

  - platform: time_date
    display_options:
      - 'date'

Thank you!

[jamesball]

I got it to work so it seems that it didn’t need to be a datetime object. The UNIX timestamp format seems to work…

[KSC]

@jamesball

I didn’t know that this tool existed - thanks for pointing it out! I found the error… I didn’t have a sensor.date entity so that is why it wouldn’t work.

Glad you figured it out! The developer template tool is one of the most frequent things I use.

[KSC]

@tom_l

I suspect your issue is because your input_datetime is not a datetime object, it is a string. datetime object methods are unavailable unless one first converts the string via strptime.

Hi, @tom_l - I checked this in the template editor and found that, as long as it’s cast using as_timestamp, it can then be used in math calcs. I added the results from the template editor on the feature-request page you referenced here: Make typed states available for entities - #5 by KSC

@jamesball - one other thing I wanted to mention is that you don’t need to use the - in the template, as in: {%- ssssss -%}. Those confused me in the beginning. They are, I think, for formatting output - which we’re not doing in a template. Just makes the code a little cleaner.

Again, glad you got it working!

[finity]

you could also eliminate the ambiguity of what might or might not work depending on the string syntax by using the “timestamp” attribute of the input_datetime.

{{ state_attr('input_datetime.air_filter_installed', 'timestamp') }}