Hmm, I thought the point of leaving this as a list was to pass through units? How does this work with e.g. datetime units?

Why would we want a list for the units machinery?

This is really old code, and I suspect predates numpy handling of masks. Maybe it should be rethought wholesale, but I don't think we do ourselves any favours unpacking the existing ndarray and turning it into a list.

I think I'm thinking of this comment https://github.com/matplotlib/matplotlib/pull/12283/files#diff-7e79bc5b4cdd21de353697e9ada248b7L3171 , and also I just fixed errorbar plotting for astropy, so was thinking this change might not play well with that; #8871. I'll check if this PR breaks the example given in that issue.

I think all that stuff was before numpy arrays could have arbitrary data in them, but I could be incorrect.

@dstansby is correct, the list is to preserve units. Some of the unit frameworks loose their units when you put them into numpy arrays like that.

OK, on the other hand this didn't fail any tests, so I guess we don't test that functionality...