code: def import_it(cls):
          
          if not cls in cls._FEATURES:
              try:
                  cls._FEATURES[cls] = cls._import_it()
              except ImportError:
                  raise cls.Error(cls._import_error_message(), cls.Error.UNSATISFIED_IMPORT_REQ)
          return cls._FEATURES[cls]
docs: Performs the import only once.