我想在嵌套饼图的内部饼图中添加一个图例：
import matplotlib.pyplot as plt
# Make data: I have 3 groups and 7 subgroups
group_names=['groupA', 'groupB', 'groupC']
group_size=[12,11,30]
subgroup_names=['A.1', 'A.2', 'A.3', 'B.1', 'B.2', 'C.1', 'C.2', 'C.3',
'C.4', 'C.5']
subgroup_size=[4,3,5,6,5,10,5,5,4,6]
# Create colors
a, b, c=[plt.cm.Blues, plt.cm.Reds, plt.cm.Greens]
# First Ring (outside)
fig, ax = plt.subplots()
ax.axis('equal')
mypie, _ = ax.pie(group_size, radius=1.3, labels=group_names, colors=
[a(0.6), b(0.6), c(0.6)] )
plt.setp( mypie, width=0.3, edgecolor='white')
# Second Ring (Inside)
mypie2, _ = ax.pie(subgroup_size, radius=1.3-0.3,
labels=subgroup_names, labeldistance=0.7, colors=[a(0.5), a(0.4),
a(0.3), b(0.5), b(0.4), c(0.6), c(0.5), …