Como criar uma única legenda para todos os subquadros em Matplotlib

import matplotlib.pyplot as plt

fig = plt.figure()
axes = fig.subplots(nrows=2, ncols=2)


for ax in fig.axes:
    ax.plot([0, 10], [0, 10], label='linear')

lines, labels = fig.axes[-1].get_legend_handles_labels()
    
fig.legend(lines, labels, loc = 'upper center')

plt.show()

lines, labels = fig.axes[-1].get_legend_handles_labels()

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(0, 10, 501)

fig = plt.figure()
axes = fig.subplots(nrows=2, ncols=2)

axes[0, 0].plot(x,
                np.sin(x),
                color = 'k',
                label="sin(x)")
axes[0, 1].plot(x,
                np.cos(x),                
                color = 'b',
                label="cos(x)")
axes[1, 0].plot(x,
                np.sin(x) + np.cos(x),
                color = 'r',
                label="sin(x)+cos(x)")
axes[1, 1].plot(x,
                np.sin(x) - np.cos(x),
                color = 'm',
                label="sin(x)-cos(x)")

lines = []
labels = []

for ax in fig.axes:
    axLine, axLabel = ax.get_legend_handles_labels()
    lines.extend(axLine)
    labels.extend(axLabel)

    
fig.legend(lines, labels,           
           loc = 'upper right')

plt.show()

for ax in fig.axes:
    axLine, axLabel = ax.get_legend_handles_labels()
    lines.extend(axLine)
    labels.extend(axLabel)