以下是使用matplotlib库绘制百分比子组柱状图的示例代码：

import matplotlib.pyplot as plt
import numpy as np

# 数据
labels = ['A', 'B', 'C', 'D']
group1 = [20, 35, 30, 10]
group2 = [15, 30, 25, 20]

# 计算每组的百分比
total1 = sum(group1)
total2 = sum(group2)
percent1 = [x / total1 * 100 for x in group1]
percent2 = [x / total2 * 100 for x in group2]

# 绘图
width = 0.35
x = np.arange(len(labels))

fig, ax = plt.subplots()
ax1 = ax.bar(x - width/2, percent1, width, label='Group 1')
ax2 = ax.bar(x + width/2, percent2, width, label='Group 2')

# 添加标签
ax.set_xticks(x)
ax.set_xticklabels(labels)
ax.set_ylabel('Percentage')

# 添加图例
ax.legend()

# 添加百分比标签
def autolabel(rects):
    for rect in rects:
        height = rect.get_height()
        ax.annotate(f'{height:.1f}%', xy=(rect.get_x() + rect.get_width() / 2, height),
                    xytext=(0, 3), textcoords="offset points",
                    ha='center', va='bottom')
autolabel(ax1)
autolabel(ax2)

plt.show()

运行以上代码，将显示一个包含两个子组的百分比柱状图，其中每个柱子表示一组数据，并显示该组数据在总数中所占的百分比。