code: def flatten(l: Iterable) -> List:
      
      rval = []
      for e in l:
          if not isinstance(e, str) and isinstance(e, Iterable):
              if len(list(e)):
                  rval += flatten(e)
          else:
              rval.append(e)
      return rval
docs: Return a list of all non-list items in l
  
      :param l: list to be flattened
      :return: