Matplotlib のすべてのサブプロットに単一の凡例を作成する方法

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)