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）

这个方法的核心，是手动的获得图中的handlers和labels，然后对它们进行切分和提取，最后分为几个legend进行显示。代码如下：

后来对下面的代码进行修改，通过handlers, labels = get_legend_handles_labels(axs=[axis])自动的获得handler。不再需要诸如handlers = [ax.scatter(range(10), [i * x for x in range(10)], label=f'Line {i}') for i in range(7)]之类的手动提取handler。源代码中这个依然进行了保留，是因为这个代码还是一个绘图过程

# -*- coding: utf-8 -*-
'''
@Time    : 2024/1/5 20:55  \n
@Author  : 月司   \n
@Email   : 815603884@qq.com \n
@File    : 图像图例的横向显示以及纵向显示.py   \n
@version : 1.0  \n
@Software: PyCharm  \n
@Desc    : 
'''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_labelsdef 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),**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: :param first_bbox_to_anchor:  `~matplotlib.transforms.BboxBase` instance, Bbox anchor of the first legend.Bbox anchor of the first legend.:param kwargs: Additional keyword arguments to pass to the legend function."""if (handlers is None) != (labels is None):  # Check if only one of handlers or labels is providedraise 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 axhandlers,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_anchorfor i in range(n_legends):start_idx = i * n_itemsend_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 = 1if i == 0:bbox_anchor = first_bbox_to_anchorelse:# 计算后续图例的bbox_to_anchorbbox_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_anchorelse:# 计算后续图例的bbox_to_anchorbbox_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)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 center', first_bbox_to_anchor=(0.2, 0.8))from matplotlib.legend import _get_legend_handles_labels as get_legend_handles_labelshandles,labels=get_legend_handles_labels([ax])plt.show()