rewrite units for plotting

[dcherian]

It would be nice if we could rewrite the units attribute when using .cf.plot() so units = "kg/m3" becomes units = "kg/m³". There must be some convenient way of doing this, maybe with pint?

cc @keewis @jthielen

[jthielen]

Yes, this could definitely be done with Pint (see the formatting options here: https://pint.readthedocs.io/en/stable/tutorial.html#string-formatting)! Though, in order to interpret CF/UDUNITS-style exponents, a custom preprocessor (like that in MetPy) is needed, which connects back to the larger issue of xarray-contrib/pint-xarray#26.

[dcherian]

Thanks.

Another option is cf_units

import cf_units

for string in ["degreeN", "m2/s4", "kg/m3", "degC"]:
    print(cf_units.Unit(string).format(cf_units.UT_UTF8))

which looks good except for the reversed order for kg/m³

°
m²·s⁻⁴
m⁻³·kg
°C

[aulemahal]

One argument against cf_units is that it is not pip-installable. It requires the UDUNITS-2 library which is not on pypi. Works well with conda, but potential headaches otherwise!