如何在Python pyplot中显示条形图中的百分比变化

import matplotlib.pyplot as plt
import numpy as np

categories = ['A', 'B', 'C', 'D']
before_values = [50, 70, 90, 60]
after_values = [70, 80, 60, 80]

percent_changes = [(after - before) / before * 100 for before, after in zip(before_values, after_values)]

fig, ax = plt.subplots()
bar_width = 0.35
index = np.arange(len(categories))

bars1 = ax.bar(index, before_values, bar_width, label='Before')
bars2 = ax.bar(index + bar_width, after_values, bar_width, label='After')

ax.set_xlabel('Categories')
ax.set_ylabel('Values')
ax.set_title('Percentage Change in Bar Chart')
ax.set_xticks(index + bar_width / 2)
ax.set_xticklabels(categories)
ax.legend()

# 添加百分比标签
for i, v in enumerate(percent_changes):
    ax.text(i, max(before_values[i], after_values[i]), f'{v:.1f}%', ha='center', va='bottom')

plt.show()