code: def flatten_unique(l: Iterable) -> List:
      
      rval = OrderedDict()
      for e in l:
          if not isinstance(e, str) and isinstance(e, Iterable):
              for ev in flatten_unique(e):
                  rval[ev] = None
          else:
              rval[e] = None
      return list(rval.keys())
docs: Return a list of UNIQUE non-list items in l