Feedback on the conversion and dimensionality functionality

[pelson]

Following the discussion in SciTools/cf-units#446 (comment), it would be good to get some feedback on how the implementation here for dimensionality and conversion works out for you @ocefpaf.

The README.md has some info, but for your is_convertible and is_dimensionless cases you can use the following:

from pyudunits2 import UnitSystem

ut_system = UnitSystem.from_udunits2_xml()

unit1 = ut_system.unit('km/h')
unit2 = ut_system.unit('meters per second')

assert unit1.is_convertible_to(unit2)
assert not unit1.is_convertible_to(ut_system.unit('m'))

And:

assert ut_system.unit('radians mg/kilogram').is_dimensionless()

There is an example in the README if you want to do actual conversions, rather than just knowing if conversions are possible.

[ocefpaf]

Phil, this is awesome. See ioos/compliance-checker#1118

That PR passes locally, for some reason the xml file is not installed when doing a pip+git install. Both is_dimensionless and is_convertible_to are working. (I did uncover a few bugs in our tests that I'll be fixing ASAP.)

[ocefpaf]

BTW, the .dimensionality() you mention in SciTools/cf-units#446 (comment) is great. Sadly my test there is not that simple. I do need to check if the unit is one of those in that list and not necessarily something that has dimensionality of meters. I'll have to re-think that part of the code.

[pelson]

for some reason the xml file is not installed when doing a pip+git install

In your PR you are doing https://github.com/pelson/pyudunits2/archive/f75f1afd27d4b66ef77fc9db9301ae914111d288.zip. If that is the pip+git you mention above, it is because that isn't pip+git 😜 - I think the way I'm using setuptools-scm means that a plain tarball won't get the XML file installed. The following seems to work though: pip install git+https://github.com/pelson/pyudunits2.git@f75f1afd27d4b66ef77fc9db9301ae914111d288. Suggest opening an issue for this if it isn't resolved by the above and I will dig into it (or just publish to pypi to make your life easier 😉).

[ocefpaf]

it is because that isn't pip+git 😜

Indeed it is not. And here I thought that going for a tarball would be easier, I would miss only the version info... Let me try a real pip from git now.

Suggest opening an issue for this if it isn't resolved by the above and I will dig into it (or just publish to pypi to make your life easier 😉).

You don't have to do that just for this test. However, if you manage to implement the date parsing, not sure of that is on your roadmap, then a first release would be great!