Imperial/Metric conversion: Where do you put your single source of truth?

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21

I tried to do this. Declared a variable in the top level of my script module: Here’s that and my function that runs on gateway startup:

import json
import system

_logger = system.util.getLogger("UnitConversion")

CONVERSIONS = {}

def load():
    """
    Runs at GATEWAY STARTUP in Linux container.
    Loads JSON and computes inverse coefficients.
    """
    global CONVERSIONS

    try:
        # Absolute path inside the container
        path = "/unitConversion.json"
        raw = system.file.readFileAsString(path)
        data = json.loads(raw)

        for src, targets in data.iteritems():
            for dst, coeffs in targets.iteritems():
                a = float(coeffs[0])
                b = float(coeffs[1])

                inv_a = 1.0 / a
                inv_b = -b

                if len(coeffs) < 4:  # avoid duplicate appends
                    coeffs.append(inv_a)
                    coeffs.append(inv_b)

        CONVERSIONS = data
        _logger.info("Unit conversions loaded successfully from {}. Contents: {}".format(path, CONVERSIONS))

    except Exception as e:
        _logger.error("Failed to load unit conversions from {}: {}".format(path, e))

What I found was that when I try to run my conversion scripts, they’d fail because CONVERSIONS would be an empty dictionary. If I went into the script console and just did a print on that variable, it’d be populated. But running it in the designer, I set my logger to report the value of that same variable as it ran the script, and it would report back “{}” as the value.

I guess I’m not understanding how this variable is supposed to work in the library script module. Alternatively, I can just write the contents of the JSON file to a memory document tag. That’s my stop-gap to getting it to work now. Is storing it in a tag versus the library script module an alright solution? Or am I not implementing it correctly?

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