def plot_grouped_bars(tick_names: List[str], data_lists: List[List], \
        colors: List[str], gap_percent: float, axis_obj = None, \
        orientation: str = 'vertical', **kwargs):
    if len(data_lists) > len(colors):
        raise ValueError
    num_data_lists = len(data_lists)
    locations_centered = np.arange(len(tick_names))

    usable_for_bars = 1.0 - (gap_percent / 100.0)
    bar_width = usable_for_bars / num_data_lists
    center_offset = (bar_width / 2.0) * (1 - num_data_lists % 2)
    tick_positions = locations_centered + usable_for_bars / 2.0
    category_starts = locations_centered + center_offset

    offset = 0.0
    for cur_height_list, cur_color in zip(data_lists, colors):
        if len(tick_names) != len(cur_height_list):
            raise ValueError
        if axis_obj:
            # AXIS object is already provided, use it
            if orientation == 'vertical':
                plt.xticks(locations_centered, tick_names)
                axis_obj.bar(category_starts + offset, cur_height_list, \
                             bar_width, color=cur_color, **kwargs)
            else:
                plt.yticks(locations_centered, tick_names)
                axis_obj.barh(category_starts + offset, cur_height_list, \
                             bar_width, color=cur_color, **kwargs)
        else:
            # AXIS object is not provided, use "plt."
            if orientation == 'vertical':
                plt.xticks(locations_centered, tick_names)
                plt.bar(category_starts + offset, cur_height_list, bar_width, \
                        color=cur_color, **kwargs)
            else:
                plt.yticks(locations_centered, tick_names)
                plt.barh(category_starts + offset, cur_height_list, bar_width, \
                        color=cur_color, **kwargs)
        offset = offset - bar_width
    # return category_starts + (bar_width / 2.0), bar_width
    return locations_centered, bar_width