RFont_designspaces.py

import more_itertools

def _as_list(item):
    return list(more_itertools.always_iterable(item))    

def _get_designspaces(self) -> list[str]:
    return _as_list(self.lib.get('public.designspaces', []))

def _set_designspaces(self, new_designspace:str | list[str]):
    self.lib['public.designspaces'] = _as_list(new_designspaces)

_designspaces = property(_get_designspaces, _set_designspaces) 

from mojo.roboFont import RFont
RFont.designspaces = _designspaces
RFont.designspace = _designspaces