enable/disable grid display

def enable_grid(self, show=None, delay_draw=False):
        "enable/disable grid display"
        if show is not None:
            self.show_grid = show
        axes = self.canvas.figure.get_axes()
        ax0 = axes[0]
        for i in ax0.get_xgridlines() + ax0.get_ygridlines():
            i.set_color(self.gridcolor)
            i.set_zorder(-1)
        axes[0].grid(self.show_grid)
        for ax in axes[1:]:
            ax.grid(False)
        if not delay_draw:
            self.canvas.draw()