The args attribute gets created by __init__ and nothing in the class
removes it. I don't think it's unreasonable for the class to expect the
attribute to not vanish on it. Possibly it should be spelled __args (or
declared private :-), but neither of those would make a difference in
this case.

Any feature access can be made more robust by checking for it in
__dict__ first, but such a practice is neither practical nor pragmatic.
It may be different for __getargs__, in which case the bug is in the
documentation for __getargs__, which should mention this issue.