'New command.'

def newTopology(self):

    for widget in self.widgetToItem.keys():
        self.deleteItem(self.widgetToItem[widget])
    self.hostCount = 0
    self.switchCount = 0
    self.controllerCount = 0
    self.links = {}
    self.hostOpts = {}
    self.switchOpts = {}
    self.controllers = {}
    self.appPrefs['ipBase'] = self.defaultIpBase
