Description

Our spectroscopy package radis depends on Astropy.units. Latest build fetched astropy==4.3
and failed with the following error :

AttributeError: module 'astropy.units' has no attribute 'imperial'

• I could find a similar error encountered by @pllim in Create a class to represent physical types #11204 (comment), which helped a lot to yield a fix, below.
• I trace the error to the change of Imports in Minor physical type updates #11592 by @namurphy :

Expected behavior

Original code worked :

import astropy.units as u
u.K in (u.K, u.imperial.deg_F)
>>> cannot import name 'imperials' from 'astropy.units'

Now I have to update the code to

import astropy.units as u
from astropy.units.imperial import deg_F 
u.K in (u.K, deg_F)
>>> True

If this is the expected behavior (and cleaner way to import), this Issue can be closed right away. Hopefully the title will help people that would encounter the same proper to find an easy fix.