Add ecg grids to the axes

def plot_ecg_grids(ecg_grids, fs, units, time_units, axes):
    "Add ecg grids to the axes"
    if ecg_grids == 'all':
        ecg_grids = range(0, len(axes))


    for ch in ecg_grids:
        # Get the initial plot limits
        auto_xlims = axes[ch].get_xlim()
        auto_ylims= axes[ch].get_ylim()

        (major_ticks_x, minor_ticks_x, major_ticks_y,
            minor_ticks_y) = calc_ecg_grids(auto_ylims[0], auto_ylims[1],
                                            units[ch], fs, auto_xlims[1],
                                            time_units)

        min_x, max_x = np.min(minor_ticks_x), np.max(minor_ticks_x)
        min_y, max_y = np.min(minor_ticks_y), np.max(minor_ticks_y)

        for tick in minor_ticks_x:
            axes[ch].plot([tick, tick], [min_y,  max_y], c='#ededed',
                          marker='|', zorder=1)
        for tick in major_ticks_x:
            axes[ch].plot([tick, tick], [min_y, max_y], c='#bababa',
                          marker='|', zorder=2)
        for tick in minor_ticks_y:
            axes[ch].plot([min_x, max_x], [tick, tick], c='#ededed',
                          marker='_', zorder=1)
        for tick in major_ticks_y:
            axes[ch].plot([min_x, max_x], [tick, tick], c='#bababa',
                          marker='_', zorder=2)

        # Plotting the lines changes the graph. Set the limits back
        axes[ch].set_xlim(auto_xlims)
        axes[ch].set_ylim(auto_ylims)