How to best run sensor reading the output of a Python script?

Installation Home Assistant OS
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1

Hi

I am new to HA. I have installed hass.io in a VM on Windows Server and everything is running. I have ssh access to the Home Assistant shell. I’m a little confused with hass.io/supevisor/ha itself and this is the first time I’ve seen yaml.

I would like to bring in some air quality information as a sensor into HA. I have a local station that publishes the raw pollutant data and I have written a short Python script to scrape it and process it to calculate some indices (it’s a piecewise linear function with some choice of maximal params). I can output this to the shell or a text file, or whatever is best. One thing to note is that I have multiple data from each scrape (levels of different pollutants) and I would like to feed them to different sensors (attributes?) in HA.

I would like to understand a hassionic way of bringing this in as a sensor. I can see a few scenarios:

  • Scrape directly in HA through the scrape sensor and replicate the mathematical operations in HA. Not sure if this is possible/appropriate in YAML. Is there some better method?

  • use the command_line sensor to run the python script and get its output. I don’t see how to get multiple sensors out without running the scrape multiple times and filtering the output differently for each sensor. Might get annoying for the data server.

  • Run the python script as a cron job every 15 mins, outputting to a text file and use the file as a data source for the sensor. Where would I set up cron? It doesn’t seem available in the HA shell, Maybe it needs to be at a lower level in the VMs? How do I access it?

Then there are some things in HACS called appdaemon and netdaemon: may this is a better way of achieving what I want? Haven’t investigated that part of HA yet.

But I may be barking up the wrong tree completely. Advice much appreciated!

Thanks!

2

I’m a fan of publishing to an mqtt broker and subscribing to the topics in Home Assistant (mqtt sensor).

Other options:

Push the values from your script directly to Home Assistant using the Home Assistant rest API ( e.g. post /api/states/<entity_id>).

Skip the Python script and scrape directly using home assistant, (scrape sensor)

3

why not create the sensor in the Python script directly? You can set the state and all attributes.

4

Could you please point me to some documentation/examples? I have no real idea of the architecture of HA yet.

Also how do I run the script in HA? in the HA shell cron doesn’t seem available?

5

How? Because maybe you could replace your Python script by a scrape or RESTful sensor?

6

There is no API at the weather station, so I have to scrape the data from a table on a webpage.

The problem is that the data are raw quantity measurements and I have to apply some simple arithmetic to get the index I want to present in the Dashboard.

Can I do algebraic transformations on scraped data within HA? It’s just a bunch of min/max functions and multiplying by constants, so it’s not very complicated, but I don’t see where I could do it.

7

Algebraic operations can be done using Template Sensors or predefined Min/Max or Statistics sensors, that consume other sensor’s values (like your scrape sensor).

8

read up on te subject: Python Scripts - Home Assistant

here’s a simple script, python_script.overview_entities:

count_all = 0
domains = []
attributes = {}

for entity_id in hass.states.entity_ids():
    count_all = count_all + 1
    entity_domain = entity_id.split('.')[0]
    if entity_domain not in domains:
        domains.append(entity_domain)

attributes['Domains'] = len(domains)
attributes['--------------'] = '-------'

for domain in sorted(domains):
    attributes[domain] = len(hass.states.entity_ids(domain))

attributes['friendly_name'] = 'Entities'
attributes['icon'] = 'mdi:format-list-numbered'

hass.states.set('sensor.overview_entities', count_all, attributes)

you can run a python script with the service python_script.name_of_the_script which will show up after you have saved the script, and reloaded the python scripts with the service python_script.reload

use the service in a HA script or automation:

  run_after_delayed_startup:
    alias: Run after delayed startup
    mode: restart
    sequence:
      - service: python_script.average_indoor_temp
# give even extra time for system to settle before doing:
      - delay:
          seconds: >
            {{states('input_number.ha_delayed_startup')|int}}
      - service: python_script.overview_entities
      - service: python_script.overview_components
      - service: script.update_entities_uun

a couple of other examples:

  - alias: Last Automation
    id: Last Automation
    trigger:
      platform: event
      event_type: automation_triggered
    condition: []
    mode: queued
    max: 50
    action:
      service: python_script.last_automation
      data:
        event: >
          {{trigger.event}}

or

  - alias: Run at startup
    id: Run at startup
    trigger:
      platform: homeassistant
      event: start
    action:
      - service: script.notify_startup
      - service: python_script.family_home
      - delay:
          seconds: >
            {{states('input_number.ha_delayed_startup')|int}}
      - event: delayed_homeassistant_start
9

Thanks for the pointers. So I have studied the Jinja2 template language and it turns out it’s quite flexible. In case anyone else is looking a this in the future, I leave here my implementation of a simple piecewise linear conversion of pollutant concentration to a CAQI subindex as a macro (function) in the template language

caqi_so3:
                name: CAQI SO3
                unit_of_measurement: " "
                # levels: 0, 50, 100, 350, 500
                select: "#content > table >tr:nth-child(27) > td:nth-child(3)"
                value_template: >
                    {% macro calc_caqi(val, range_top, range_bot, caqi_top, caqi_bot) -%}
                    {{ '%0.1f'|format(caqi_bot + (caqi_top-caqi_bot)/(range_top-range_bot)*(val-range_bot)) }}
                    {%- endmacro %}
                    {% set levels = [500,350,100,50,0] %}
                    {% set caqi_levels = [100,75,50,25,0] %}
                    {% set sensor = float(value) %}
                    {% if sensor >levels[0] -%}
                    {{'%0.1f'|format(caqi_levels[0] + (caqi_levels[0]-caqi_levels[1])/(levels[0]-levels[1])*(val-levels[1])) }}
                    {%- elif sensor >= levels[1] -%}
                    {{calc_caqi(sensor,levels[0],levels[1],caqi_levels[0],caqi_levels[1]) }}
                    {%- elif sensor >= levels[2] -%}
                    {{calc_caqi(sensor,levels[1],levels[2],caqi_levels[1],caqi_levels[2]) }}
                    {%- elif sensor >= levels[3] -%}
                    {{calc_caqi(sensor,levels[2],levels[3],caqi_levels[2],caqi_levels[3]) }}
                    {%- elif sensor >= levels[4] -%}
                    {{calc_caqi(sensor,levels[3],levels[4],caqi_levels[3],caqi_levels[4]) }}
                    {%- else -%}
                    N/A
                    {%- endif %}