code: def retrieveVals(self):
          
          for iface in self._ifaceList:
              stats = self._ifaceStats.get(iface)
              graph_name = 'netiface_traffic_%s' % iface
              if self.hasGraph(graph_name):
                  self.setGraphVal(graph_name, 'rx', stats.get('rxbytes') * 8)
                  self.setGraphVal(graph_name, 'tx', stats.get('txbytes') * 8)
              graph_name = 'netiface_errors_%s' % iface
              if self.hasGraph(graph_name):
                  for field in ('rxerrs', 'txerrs', 'rxframe', 'txcarrier',
                      'rxdrop', 'txdrop', 'rxfifo', 'txfifo'):
                      self.setGraphVal(graph_name, field, stats.get(field))
docs: Retrieve values for graphs.