code: def getDevStats(self, dev, devtype = None):
          
          if devtype is not None:
              if self._devClassTree is None:
                  self._initDevClasses()
              if devtype <> self._mapDevType.get(dev):
                  return None
          return self._diskStats.get(dev)
docs: Returns I/O stats for block device.
          
          @param dev:     Device name
          @param devtype: Device type. (Ignored if None.)
          @return:        Dict of stats.