Python matplotlib

width=4
height=width*0.618
fig, ax = plt.subplots(figsize=(width, height))

title='ZZZ'

x1=[1, 2., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
y1=[0., 0.5, 0.75, 0.86, 0.87, 0.88,0.86, 0.86, 0.87, 0.86,0.88, 0.87, 0.88]
label1='A'
style1=['8', 'g', (0, (5, 1))]

x2=[1, 2., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
y2=[0., 0.3, 0.6, 0.65, 0.66, 0.64,0.65, 0.65, 0.64, 0.66,0.65, 0.66, 0.65]
label2='B'
style2=['s', 'orange', (0, (2, 1))]

x3=[1, 2., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
y3=[0., 0.2, 0.43, 0.46, 0.47,0.47, 0.46, 0.46, 0.48, 0.47,0.46, 0.47, 0.47]
label3='C'
style3=['v', 'r', (0, (4, 1, 1, 1, 1, 1))]

ax.legend() 由 3 种调用方式

Call signatures:

legend()
legend(labels)
legend(handles, labels)

ax.plot(x1,y1,marker=style1[0],color=style1[1],linestyle=style1[2],label=label1)
ax.plot(x2,y2,marker=style2[0],color=style2[1],linestyle=style2[2],label=label2)
ax.plot(x3,y3,marker=style3[0],color=style3[1],linestyle=style3[2],label=label3)

ax.legend() # 自动添加图例

使用 get_legend_handles_labels() 手动添加图例，效果和 ax.legend() 一样

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles, labels)

但是，如果我们只传入部分 handles, 即

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles[:1], labels[:1])

得到

好像只要出现几个图例由 handles 决定，不管 labels, 即

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles[:1], labels)

效果也只有 label1, 和图 2 一样

但是如果只是传入 handles 这样，程序会报错

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles)

# TypeError: A single argument passed to legend() must be a list of labels, but found an Artist in there.

根据 ax.legend() 3种调用方式可以得知

Call signatures:

legend()
legend(labels)
legend(handles, labels)

在只有一个参数的情况下，我们需要使用 labels

handles, labels = ax.get_legend_handles_labels()
ax.legend(labels[1:])

得到

此时我们发现一个问题，就是绿色的线应该标成 label1, 这里是因为按照默认自动的排序

假如现在只标记 黄色 和 红色 的线

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles[1:], labels[1:])

有更简单的方法是

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles=handles[1:])

一样得到图 4 的效果

h1,=ax.plot(x1,y1,marker=style1[0],color=style1[1],linestyle=style1[2],label=label1)
h2,=ax.plot(x2,y2,marker=style2[0],color=style2[1],linestyle=style2[2],label=label2)
h3,=ax.plot(x3,y3,marker=style3[0],color=style3[1],linestyle=style3[2],label=label3)

ax.legend(handles=[h2,h3])

得到

甚至我们可以在 legend() 函数中重新修改 label

ax.legend(handles=[h2,h3],labels=['new label2','new label3'])

现在我们添加一条 蓝色 的图例，但是没有数据

这个功能主要用于某些画图函数无法直接生成图例，比如 violin 函数 ax.violinplot()

h1,=ax.plot(x1,y1,marker=style1[0],color=style1[1],linestyle=style1[2],label=label1)
h2,=ax.plot(x2,y2,marker=style2[0],color=style2[1],linestyle=style2[2],label=label2)
h3,=ax.plot(x3,y3,marker=style3[0],color=style3[1],linestyle=style3[2],label=label3)

import matplotlib.lines as mlines

blue_line = mlines.Line2D([], [], color='#2F81BA',linestyle=(0,(4,1)), marker='*',label='Blue')

ax.legend(handles=[h1,h2,h3,blue_line])

注意，所有的图例都要写在一起，如果 h1, h2, h3 用一次 ax.legend(), blue_line 用一次 ax.legend(), 只会显示最后那个图例。

ax.legend(handles=[h1,h2,h3])
ax.legend(handles=[blue_line])

import os

import matplotlib.pyplot as plt
import time

font1 = {
    'weight': 'medium',
    'size': 12,
}

font2 = {
    'weight': 'medium',
    'size': 12,
}


def pt():

    width = 4
    height = width * 0.618
    fig, ax = plt.subplots(figsize=(width, height))

    title = 'ZZZ'

    x1 = [1, 2., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
    y1 = [
        0., 0.5, 0.75, 0.86, 0.87, 0.88, 0.86, 0.86, 0.87, 0.86, 0.88, 0.87,
        0.88
    ]
    label1 = 'label1'
    style1 = ['8', 'g', (0, (5, 1))]

    x2 = [1, 2., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
    y2 = [
        0., 0.3, 0.6, 0.65, 0.66, 0.64, 0.65, 0.65, 0.64, 0.66, 0.65, 0.66,
        0.65
    ]
    label2 = 'label2'
    style2 = ['s', 'orange', (0, (2, 1))]

    x3 = [1, 2., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
    y3 = [
        0., 0.2, 0.43, 0.46, 0.47, 0.47, 0.46, 0.46, 0.48, 0.47, 0.46, 0.47,
        0.47
    ]
    label3 = 'label3'
    style3 = ['v', 'r', (0, (4, 1, 1, 1, 1, 1))]

    h1, = ax.plot(x1,
                  y1,
                  marker=style1[0],
                  color=style1[1],
                  linestyle=style1[2],
                  label=label1)
    h2, = ax.plot(x2,
                  y2,
                  marker=style2[0],
                  color=style2[1],
                  linestyle=style2[2],
                  label=label2)
    h3, = ax.plot(x3,
                  y3,
                  marker=style3[0],
                  color=style3[1],
                  linestyle=style3[2],
                  label=label3)

    import matplotlib.lines as mlines

    blue_line = mlines.Line2D([], [],
                              color='#2F81BA',
                              linestyle=(0, (4, 1)),
                              marker='*',
                              label='Blue')

    ax.legend(handles=[h1, h2, h3, blue_line])
    # ax.legend(handles=[blue_line])

    ax.set_ylabel('YYY', font2)
    ax.set_xlabel('XXX', font1)

    ax.set_title('TITLE = ' + title, fontsize=11)
    ax.grid()

    plt.tight_layout()

    SaveDir = 'result/'
    if not os.path.exists(SaveDir):
        os.makedirs(SaveDir)
    now = time.strftime("%Y_%m%d_%H%M_%S", time.localtime(
        time.time()))  # 获得当前时间 2021_1108_2310_22
    SaveFile = SaveDir + title + '_' + now + '.png'  
    fig.savefig(SaveFile)
    print(SaveFile + ' ==================>>> has been complete')
    plt.close()


def example():
    pt()


if __name__ == '__main__':

    example()

legend guide