可以添加椭圆的长轴和短轴。
在我展示的代码中，我做了主轴，但你需要处理Angular 部分（基于椭圆的点），而我只是将其设置为45度以快速回答。
这样做的结果将给予完整的解答。
所以，我做了这样的事情：

import matplotlib.patches as patches
import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots(subplot_kw={'aspect': 'equal'})
#################################
# you need to figure this bit out
#################################

ellipse = patches.Ellipse((0, 0), 4, 2, angle=45, fill=False)
ax.add_artist(ellipse)

ellipse.set_clip_box(ax.bbox)
ellipse.set_alpha(0.1)
ax.annotate("",
            xy=(ellipse.center[0], ellipse.center[1] - ellipse.height / 2),
            xytext=(ellipse.center[0], ellipse.center[1] + ellipse.height / 2),
            arrowprops=dict(arrowstyle="<->", color="black"))
ax.annotate("",
            xy=(ellipse.center[0] - ellipse.width / 2, ellipse.center[1]),
            xytext=(ellipse.center[0] + ellipse.width / 2, ellipse.center[1]),
            arrowprops=dict(arrowstyle="<->", color="black"))
ax.annotate("",
            xy=(ellipse.center[0] - ellipse.width / 2 * np.cos(np.deg2rad(ellipse.angle)), 
                ellipse.center[1] - ellipse.height / 2 * np.sin(np.deg2rad(ellipse.angle))),
            xytext=(ellipse.center[0] + ellipse.width / 2 * np.cos(np.deg2rad(ellipse.angle)), 
                    ellipse.center[1] + ellipse.height / 2 * np.sin(np.deg2rad(ellipse.angle))),
            arrowprops=dict(arrowstyle="<->", color="black"))

ax.set_xlim(-2.2, 2.2)
ax.set_ylim(-2.2, 2.2)

plt.show()

这就给你留下了这样一个情节：

基本上，总而言之，anotate行让您完成所需的最后几位。
编辑：我可以简化为：

import matplotlib.patches as patches
import matplotlib.pyplot as plt

fig, ax = plt.subplots(subplot_kw={'aspect': 'equal'})

# patches.Ellipse(center, width, height, angle)
ellipse = patches.Ellipse((0, 0), 4, 2, angle=45, fill=False)
ax.add_artist(ellipse)

ellipse.set_clip_box(ax.bbox)

ax.annotate("",
            xy=(ellipse.center[0] - ellipse.width+2 , 
                ellipse.center[1] - ellipse.height ),
            xytext=(ellipse.center[0] + ellipse.width-1, 
                    ellipse.center[1] + ellipse.height+1),
            arrowprops=dict(arrowstyle="<->", color="red"))
ax.set_xlim(-2.2, 2.2;)
ax.set_ylim(-2.2, 2.2)

plt.show()

它看起来像这样：

from math import sin, cos, radians
import matplotlib.patches as patches
import matplotlib.pyplot as plt

fig, ax = plt.subplots(subplot_kw={'aspect': 'equal'})

##############
ellipse_size = (4,2)
ellipse_rotation = 45
ellipse_position = (0,0)

ellipse = patches.Ellipse(ellipse_position, ellipse_size[0], ellipse_size[1], angle=ellipse_rotation, fill=False)
ax.add_artist(ellipse)

ax.set_xlim(-2.2, 2.2)
ax.set_ylim(-2.2, 2.2)

# math for the start and end axis point positions
ax1_points = [
    (ellipse_position[0]+ellipse_size[0]/2*cos(radians(ellipse_rotation)), 
    ellipse_position[1]+ellipse_size[0]/2*sin(radians(ellipse_rotation))),
    (ellipse_position[0]+ellipse_size[0]/2*cos(radians(ellipse_rotation + 180)), 
    ellipse_position[1]+ellipse_size[0]/2*sin(radians(ellipse_rotation + 180)))
    ]
ax2_points = [
    (ellipse_position[0]+ellipse_size[1]/2*cos(radians(ellipse_rotation+90)), 
    ellipse_position[1]+ellipse_size[1]/2*sin(radians(ellipse_rotation+90))),
    (ellipse_position[0]+ellipse_size[1]/2*cos(radians(ellipse_rotation + 270)), 
    ellipse_position[1]+ellipse_size[1]/2*sin(radians(ellipse_rotation + 270)))]

# ax1 and ax2 contains the start and the end point of the axis ([x,y] format)

# drawing the arrows
arrowprops=dict(arrowstyle="<->", color="red")
ax.annotate("", xy=ax1_points[0], xytext=ax1_points[1], arrowprops=arrowprops)
ax.annotate("", xy=ax2_points[0], xytext=ax2_points[1], arrowprops=arrowprops)
plt.show()

产生这样的结果：

希望这对你有帮助。