units_compatible does not take pint.Unit as arguments type

[nollety]

The signature of units_compatible() says that its arguments must be of type pint.Unit, however the following code:

import pint
from pinttr.util import units_compatible

units_compatible(pint.Unit("m"), pint.Unit("km"))

raises

AttributeError: 'Unit' object has no attribute '_get_non_multiplicative_units'

whereas:

ureg = pint.UnitRegistry()
units_compatible(ureg("m"), ureg("km"))

works fine, which suggests that the arguments type of units_compatible() is pint.Quantity, instead of pint.Unit?

[leroyvn]

ureg("m") and ureg("km") are both pint.Unit instances with registry ureg. If you check the Pint docs, you'll find out that you actually should never use pint.Unit or pint.Quantity right on; instead, you must create them from a registry.

So my answer is: you simply should not do something like pint.Unit("m"): it will not be compatible with any other unit.

[leroyvn]

To be more concrete, this will raise the exception you mentioned as well:

1. * pint.Unit("m")

and this will work:

assert isinstance(ureg.Unit("m"), pint.Unit)

[nollety]

Ah, I'm sorry, I have not read that part of the Pint docs... Thank you for the explanation!