Some context:  I noticed this while discussing (in a course) a programming trick involving instance initialization and locals() that I'd encountered in the past:

    def _init(locs):
        self = locs.pop('self')
        for name, val in locs.items():
            setattr(self, name, val)

    class Spam:
        def __init__(self, a, b, c, d):
            _init(locals())

In looking at locals(), it was coming back in reverse order of method arguments (d, c, b, a, self).   To be honest, it wasn't a critical matter, but more of an odd curiosity in light of recent dictionary ordering.

I could imagine writing a slightly more general version of _init() that didn't depend on a named 'self' argument if order was preserved:

    def _init(locs):
       items = list(locs.items())
       _, self = items[0]
       for name, val in items[1:]:
           setattr(self, name, val)

Personally, I don't think the issue Nathaniel brings up is worth worrying about because it would be such a weird edge case on something that is already an edge case.  Returning variables in "lexical order"--meaning the order in which first encountered in the source seems pretty sensible to me.