text: class InvalidBackendError(Exception):
      """
      InvalidBackendError is raised when instances of BackendPool
      can't get a backend implementation
      """
  
      def __init__(self, backend_type, backend_id, available_backends):
          self.backend_type = backend_type
          self.backend_id = backend_id
          self.available_backends = available_backends
          self.error_message = 'Invalid {} backend: {}'.format(
              self.backend_type, self.backend_id
          )
  
          super(InvalidBackendError, self).__init__(
              self.backend_type,
              self.backend_id,
              self.error_message,
              self.available_backends,
          )
  