my matplotlib realtime plot doesn't show the line between the points

[Nicolas Marat]

sorry that the real piece of code




        self.MplWidget.canvas.axes.set_xlim(left=max(0, self.i-40), right= self.i+60)
        self.MplWidget.canvas.axes.plot(x, y,'.k-')
        self.MplWidget.canvas.axes.set_title('pull')
        self.MplWidget.canvas.draw()