我们将图例进行行显示或者列显示后，只能想继续赋予不同行或者列不同的title来进行分类。比较简单的方式，就是通过ax.annotate方法添加标签，这样方法复用率比较低，每次使用都要微调ax.annotate的显示位置。比较方便的方法是在案例1实现的基础上，添加title显示的功能。

motplotlib图例案例1：通过多个legend完全控制图例显示顺序（指定按行排序 or 按列排序）

添加title显示功能后的代码：

import matplotlib.pyplot as plt
import matplotlib.axes
from typing import List, Tuple, Any
#这个函数可以获得axis对象的已经绘制的artist中的所有的hander和labels，这个可以只给它一个axis参数。注意这个参数需要是列表类的。
from matplotlib.legend import _get_legend_handles_labels as get_legend_handles_labels

def custom_legend_layout(axis: matplotlib.axes.Axes,
                         handlers: List[Any]=None,
                         labels: List[str]=None,
                         n_items: int = 3,
                         offset: float = 0.05,
                         vertical: bool = False,
                         loc: str = 'upper right',
                         first_bbox_to_anchor: Tuple[float, float] = (1, 1),
                         title:List[str]=None,
                         title_shift:List[Tuple[float,float]]=None,
                         **kwargs) -> None:
    """
    A function to arrange legend items in a custom layout.

    :param axis: Axis object on which to place the legends.
    :param lines: List of line objects to include in the legends.
    :param labels: List of labels corresponding to the line objects.
    :param n_items: Number of items per row (if vertical=False) or column (if vertical=True).
    :param offset: Vertical offset between rows (or horizontal offset between columns if vertical=True).
    :param vertical: If True, legends are arranged vertically, otherwise horizontally.
    :param loc: Location anchor for all legends.
    :param first_bbox_to_anchor:  `~matplotlib.transforms.BboxBase` instance，Bbox anchor of the first legend.
    :param kwargs: Additional keyword arguments to pass to the legend function.
    """
    va_dict={
        "center":'center',
        "lower":'top',
        "upper":'bottom'
    }

    ha_dict={
        "center": 'center',
        "right":"left",
        "left":"right",
    }

    if (handlers is None) != (labels is None):  # Check if only one of handlers or labels is provided
        raise ValueError("Both 'handlers' and 'labels' must be specified if one is provided.")

    if (handlers is None) and (labels is None): # get default handlers and labels from ax
        handlers,labels=get_legend_handles_labels(axs=[axis]) # note:  the param axs is list object

    # 确保n_items不为0，避免除以0的错误
    n_items = max(1, n_items)
    # 计算需要多少个图例
    n_legends = len(handlers) // n_items + (1 if len(handlers) % n_items else 0)

    # 计算每个图例的bbox_to_anchor
    for i in range(n_legends):
        start_idx = i * n_items
        end_idx = min(start_idx + n_items, len(handlers))
        legend_lines = handlers[start_idx:end_idx]
        legend_labels = labels[start_idx:end_idx]

        if vertical:
            # 对于垂直布局
            ncol = 1
            if i == 0:
                bbox_anchor = first_bbox_to_anchor
            else:
                # 计算后续图例的bbox_to_anchor
                bbox_anchor = (first_bbox_to_anchor[0] + i * offset, first_bbox_to_anchor[1])
        else:
            # 对于水平布局
            ncol = len(legend_lines)
            if i == 0:
                bbox_anchor = first_bbox_to_anchor
            else:
                # 计算后续图例的bbox_to_anchor
                bbox_anchor = (first_bbox_to_anchor[0], first_bbox_to_anchor[1] - i * offset)

        legend = axis.legend(legend_lines, legend_labels, loc=loc, bbox_to_anchor=bbox_anchor, ncol=ncol, frameon=False, **kwargs)
        axis.add_artist(legend)
        # 计算每个title的位置
        va_key,ha_key=loc.split(" ")
        if title and len(title)==n_legends:

            w_shift= title_shift[i][0] if title_shift else 0
            h_shift=title_shift[i][1] if title_shift else 0

            axis.annotate(
                text=title[i],
                xy=(bbox_anchor[0]+w_shift, bbox_anchor[1]+h_shift),
            xycoords='axes fraction',
            va=va_dict[va_key],
            ha=ha_dict[ha_key]
            )

if __name__ == '__main__':


    # 示例使用这个函数
    fig, ax = plt.subplots()
    handlers = [ax.scatter(range(10), [i * x for x in range(10)], label=f'Line {i}') for i in range(7)]

    # 调用函数，横向排列图例
    custom_legend_layout(ax, n_items=3, offset=0.25, vertical=True,
                         loc='upper left', first_bbox_to_anchor=(0.2, 0.8),
                         title=["title 1","title 2","title 3"],
                         #title_shift=[(-0.1,0),(-0.1,0),(-0.1,0)],
                         )


    from matplotlib.legend import _get_legend_handles_labels as get_legend_handles_labels

    handles,labels=get_legend_handles_labels([ax])

    plt.show()

运行后：