How/where to store calibration values - written by program A, read by program B

[DL Neil]

On 12/6/23 03:37, Chris Green via Python-list wrote:
> Is there a neat, pythonic way to store values which are 'sometimes'
> changed?
> 
> My particular case at the moment is calibration values for ADC inputs
> which are set by running a calibration program and used by lots of
> programs which display the values or do calculations with them.
> 
>  From the program readability point of view it would be good to have a
> Python module with the values in it but using a Python program to
> write/update a Python module sounds a bit odd somehow.
> 
> I could simply write the values to a file (or a database) and I
> suspect that this may be the best answer but it does make retrieving
> the values different from getting all other (nearly) constant values.
> 
> Are there any Python modules aimed specifically at this sort of
> requirement?

Another programming-term for these might be "environment variables". 
However, be aware that such also has a specific meaning at the Operating 
System level.

1 Sysops Environment Variables exist completely outside the code. Python 
interrogates the Sysops to fetch/set them. Can be problematic because 
only apply on single machine and are not part of change-control, VS, etc.

2 A .con file (in my tradition, likely still .uni type in MSFT) or 
similar, which contains the key:value pairs recommended elsewhere. There 
are formal .con and .uni (etc) formats. Most of the teams I've 
worked-with recently seem to settle on .JSON files which are 
very-conveniently structured as (read into/written from) a Python 
dictionary, and a single function-call interaction.

Word of warning/voice of [bitter] experience: ALWAYS *trumpet* any 
changes in these values AND output them (as you would any "assumptions" 
for a calculation) at the top of output reports. The trouble is that 
humans assume continuity but such an arrangement is NOT idempotent - 
which leads to complaints: "I ran it on Monday and got these results, 
but when I ran it again on Tuesday, the results changed"...

Yes there are Python libraries. Choose your method/format first, and 
then search - either Duckboards or straight from Pepi.

I have systems which use an DBMS for environment variables, but (a) only 
when there's a significant number, and (b) when the application is 
already connecting to the DBMS for processing [and maybe (c) because I 
know my way around such tools so they're 'easy']. Not recommended!

-- 
Regards =dn