docs: def listify(arg):
      """
      Simple utility method to ensure an argument provided is a list. If the
      provider argument is not an instance of `list`, then we return [arg], else
      arg is returned.
  
      :type arg: list
      :rtype: list
      """
      if isinstance(arg, (set, tuple)):
          # if it is a set or tuple make it a list
          return list(arg)
      if not isinstance(arg, list):
          return [arg]
      return arg