How to pass info from one sensor to another?

Development
1

Hi,
i want to ask for your opinion. I wanted to use the alpha_vantage platform which pulls currency exchange rates as well as stock prices by querying the alpha vantage api.
For stocks you can configure a currency: attribute, but this is only used to display the related icon and to set the unit_of_measurement. It does not mean that the stock price is converted to a desired currency.
For example

symbols:

  • symbol: GOOGL
    name: Google
    currency: EUR

Will show a Euro € in the gui, but the numeric value is still the price in Dollar (or whatever currency the Api returns together with the numeric value)

Now i started to introduce a new attribute convert_currency like this

symbols:

  • symbol: GOOGL
    name: Google
    currency: EUR
  • symbol: FLT.V
    name: Drone Delivery Canada
    currency: EUR
    convert_currency: USD_EUR

foreign_exchange:

  • name: USD_EUR
    from: USD
    to: EUR

This means: Alpha Vantage Api returns the price for FLT.V in USD, the price should be converted to EUR using the conversion rate which the sensor USD_EUR already “knows”.
This happens in the update-method of Entity FLT.V

Now my question: i implemented two methods how the conversion rate is transferred from Entity USD_EUR to Entity FLT.V

  1. Entity FLT.V runs self._hass.states.get(“sensor.usd_eur”)
  2. Entity USD_EUR writes the result of an update to self._hass.data[“DATA_alpha_vantage_USD_EUR”] where entity FLT.V reads it

What would be the proper way in homeassistant? Calling this internal Api or using shared memory?

Gerhard

2

Personally, I’d go with the first method. States are basically a big global variable. So if the information is already there, why duplicate it in the data dictionary?

3

Yes, that sounds reasonable. I’ll use the states.get(). My concern was that calls to the “internal api” would put more load on the system than a memory copy, but that’s nonsense for something that happens once a minute or less.
Gerhard