code: def notify(self, resource):
          
          observers = self._observeLayer.notify(resource)
          logger.debug("Notify")
          for transaction in observers:
              with transaction:
                  transaction.response = None
                  transaction = self._requestLayer.receive_request(transaction)
                  transaction = self._observeLayer.send_response(transaction)
                  transaction = self._blockLayer.send_response(transaction)
                  transaction = self._messageLayer.send_response(transaction)
                  if transaction.response is not None:
                      if transaction.response.type == defines.Types["CON"]:
                          self._start_retransmission(transaction, transaction.response)
  
                      self.send_datagram(transaction.response)
docs: Notifies the observers of a certain resource.
  
          :param resource: the resource