code: def perform_import(val, setting_name):
      
      if val is None:
          return None
      elif isinstance(val, six.string_types):
          return import_from_string(val, setting_name)
      elif isinstance(val, (list, tuple)):
          return [import_from_string(item, setting_name) for item in val]
      return val
docs: If the given setting is a string import notation,
      then perform the necessary import or imports.