Understandable! This is because `-a 1 2 3` assiging a = [1, 2, 3] is not GNU style.

If you want that, the GNU style could be `-a "1 2 3"`.

Normally `-a 1 2 3` would be a = 1, and 2 and 3 being positional arguments. A clarified way to write the same would be `-a 1 -- 2 3`.