'update the slider position'

def _update(self, event):

    if self.ignore(event):
        return
    if (event.button != 1):
        return
    if ((event.name == u'button_press_event') and (event.inaxes == self.ax)):
        self.drag_active = True
        event.canvas.grab_mouse(self.ax)
    if (not self.drag_active):
        return
    elif ((event.name == u'button_release_event') or ((event.name == u'button_press_event') and (event.inaxes != self.ax))):
        self.drag_active = False
        event.canvas.release_mouse(self.ax)
        return
    val = self._value_in_bounds(event.xdata)
    if (val is not None):
        self.set_val(val)
