Single legend item with two lines

Question

I\'d like to generate a custom matplotlib legend which, for each entry has two lines for each label as shown in this example:

From some researc

Answer 1

Here is an inadequate solution I have come to after playing around. I post it in case it helps others, but would prefer to do it properly. It uses two columns and the label of the first as a '/' or one could equally use "and".

import matplotlib.pyplot as plt

x = np.linspace(0, 3)
fig, axL = plt.subplots()
axR = axL.twinx()

axL.plot(x, np.sin(x), color='k', label='/')
axR.plot(x, 100*np.cos(x), color='r', label='label')

axL.set_ylabel('sin(x)', color='k')
axR.set_ylabel('100 cos(x)', color='r')
axR.tick_params('y', colors='r')

handlesL, labelsL = axL.get_legend_handles_labels()
handlesR, labelsR = axR.get_legend_handles_labels()
handles = handlesL + handlesR
labels = labelsL + labelsR
axR.legend(handles, labels, loc='lower center', ncol=2, fontsize=16,
           handletextpad=0.4, columnspacing=0.4)