也许最简单的方法是创建相应数量的Patch实例:
import matplotlib.patches as mpatches
import matplotlib.pyplot as plt
import numpy as np
data = np.random.randint(8, size=(100,100))
cmap = plt.cm.get_cmap('PiYG', 8)
plt.pcolormesh(data,cmap = cmap,alpha = 0.75)
# Set borders in the interval [0, 1]
bound = np.linspace(0, 1, 9)
# Preparing borders for the legend
bound_prep = np.round(bound * 7, 2)
# Creating 8 Patch instances
plt.legend([mpatches.Patch(color=cmap(b)) for b in bound[:-1]],
['{} - {}'.format(bound_prep[i], bound_prep[i+1] - 0.01) for i in range(8)])