self.fig = figure()
    self.ax = self.fig.add_subplot(111)
    self.ax.set_ylim( min(y), max(y) )

    self.line, = self.ax.semilogx(x,y,'.-')   #tuple of a single element
    self.canvas = FigureCanvasTkAgg(self.fig,master=master)
    self.ax.semilogx(x,y,'o-')
    self.canvas.show()
    self.canvas.get_tk_widget().pack(side='top', fill='both', expand=1)
    self.frame.pack()

#call the clear method on your axes
self.ax.clear()

#plot the new data
self.ax.set_ylim(min(newy), max(newy))
self.ax.semilogx(newx, newy, 'o-')

#call the draw method on your canvas
self.canvas.draw()