graph command

def cmd_graph(self, args):
        '''graph command'''
        if len(args) == 0:
            # list current graphs
            for i in range(len(self.graphs)):
                print("Graph %u: %s" % (i, self.graphs[i].fields))
            return

        elif args[0] == "help":
            print("graph <timespan|tickresolution|expression>")
        elif args[0] == "timespan":
            if len(args) == 1:
                print("timespan: %.1f" % self.timespan)
                return
            self.timespan = float(args[1])
        elif args[0] == "tickresolution":
            if len(args) == 1:
                print("tickresolution: %.1f" % self.tickresolution)
                return
            self.tickresolution = float(args[1])
        else:
            # start a new graph
            self.graphs.append(Graph(self, args[:]))