您需要自己创建图例。为此，创建一些未在图中显示的矩形（所谓的代理艺术家）。
#create legend
handles = [Rectangle((0,0),1,1,color=c,ec="k") for c in [low,medium, high]]
labels= ["low","medium", "high"]
plt.legend(handles, labels)
完整的例子：
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.patches import Rectangle
data = np.random.rayleigh(size=1000)*35
N, bins, patches = plt.hist(data, 30, ec="k")
cmap = plt.get_cmap('jet')
low = cmap(0.5)
medium =cmap(0.25)
high = cmap(0.8)
for i in range(0,4):
patches[i].set_facecolor(low)
for i in range(4,11):
patches[i].set_facecolor(medium)
for i in range(11,30):
patches[i].set_facecolor(high)
#create legend
handles = [Rectangle((0,0),1,1,color=c,ec="k") for c in [low,medium, high]]
labels= ["low","medium", "high"]
plt.legend(handles, labels)
plt.xlabel("Watt Hours", fontsize=16)
plt.ylabel("Households", fontsize=16)
plt.xticks(fontsize=14)
plt.yticks(fontsize=14)
plt.gca().spines["top"].set_visible(False)
plt.gca().spines["right"].set_visible(False)
plt.show()
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