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hgrecco / pint

Operate and manipulate physical quantities in Python
http://pint.readthedocs.org/
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Q: Is it possible to encode a substance type? #991

Closed cwerner closed 4 years ago

cwerner commented 4 years ago

Hi.

Very fresh user of the library so I might be missing something. I'm looking for a solution to the following use case (also, I'd +1 for a discourse channel to discuss the use of this great library):

I work with environmental data (greenhouse gas fluxes) and want to encode the units into my computations.

Now, this works fine for basic calculations (i.e. kg ha-1 * area), however I usually have emissions like N2O, NOx or CH4 and their quantities are given in kg N ha-1 or kg C ha-1, respectively

Question 1: Can I somehow enforce a check that additions of N-based substances work, but for instance 12 kg N2O-N + 6 kg CH4-C gives an error? Would I need to redefine kg for that or can the chemistry context help?

Question 2: For N2O, CH4 or CO2 we often convert to CO2-eq (global worming potential, GWP). This is basically a ratio to convert from N2O-> CO2-eq (factor 285) or from CH4->CO2-eq (28). After the conversion the variables can be added up (i.e. the GWP). How would one do that?

Cheers

hgrecco commented 4 years ago

In general, I would argue that this type of higher level checks should be in a different package that use pint. Having said that, there was a discusion to annotate quantities, which could allow user defined checks. Look up "Role" in the tracker.

cwerner commented 4 years ago

Ah, ok. I’ll try to check out the role() discussion. Thanks

hgrecco commented 4 years ago

And if that does not suit your needs, start a package that uses pint. We will be happy to support you.

cwerner commented 4 years ago

Thanks. I'll try to learn a bit more about pint and then maybe try to create a small package as suggested. My first idea would be to subclass Quantity and customise it slightly... Cheers