如何在matplotlib图中添加海轴和子图？

import matplotlib.pyplot as plt
import matplotlib.gridspec as gridspec

fig = plt.figure(figsize=(8, 6))
gs = gridspec.GridSpec(2, 2, width_ratios=[1, 2], height_ratios=[2, 1])

ax1 = plt.subplot(gs[0, 0])
ax2 = plt.subplot(gs[0, 1])
ax3 = plt.subplot(gs[1, :])

ax1.plot(x1, y1)
ax2.plot(x2, y2)
ax3.plot(x3, y3)

ax4 = ax3.twinx()
ax4.plot(x4, y4, 'r')

ax1.set_title('Subplot 1')
ax2.set_title('Subplot 2')
ax3.set_title('Subplot 3')
ax4.set_ylabel('Secondary Y-axis')

plt.tight_layout()

plt.show()