Allow users to add custom units

[rju]

Wee are developing multiple special languages (domain-specific languages (DSLs)) for configuration, bio-geo-chemical models and testing for model code which use mostly SI units, but in certain areas also use other custom units. These DSLs use therefore units to ensure safety and perform necessary unit conversions if necessary. When moving from the early prototypes in Java to Python, as this language is more widely used in science, we came across your cf_units library which almost fits our purpose. The only missing part are custom units. You already added ppm and dB yourself. However, we want to be able to add arbitrary units to the system.

To test whether this is possible, we already created a fork over at Codeberg and could contribute it to your code base. If it is sufficient in quality as a contribution.

https://codeberg.org/prefec2/cfunits/src/branch/add-special-units

In our example we also added a small script to showcase the usage called cf_test.py

Sorry for not using the correct template for feature requests. I could not find them.

[davidhassell]

Hi @rju,

Thanks for this. As I understand it, you'd like to add a new "new_units" class method that defines a new unit for the duration of the session, and that each new unit would be a new base unit (in the sense of the seven SI base units). Is that right? Sounds like good idea and generally useful feature, which we'd like to have.

Would it be OK you to create a Pull Request from the code you've written (see https://ncas-cms.github.io/cfunits/contributing.html#preparing-pull-requests)? Then it will be easy to test and review.

All the best,
David

[rju]

I'll do. Thanks for considering it.
I've created a pull request. Id is 59