docs: def get_plugin_class(self, typ):
          """
          get class by name
          """
          if typ in self._class:
              return self._class[typ]
  
          # try to import by same name
          try:
              importlib.import_module("%s.%s" % (self.namespace, typ))
              if typ in self._class:
                  return self._class[typ]
  
          except ImportError as e:
              self.log.debug("ImportError " + str(e))
  
          raise ValueError("unknown plugin '%s'" % typ)