[Python] matplotlib.plt adds an unwanted line when using fill_between

Question about using fill_between:

Using fill_between in the following snippet adds an unwanted vertical and horizontal line. Is it because of the parametric equation? How can I fix it?

import matplotlib.pyplot as plt
import numpy as np
t = np.linspace(0, 2 * np.pi, 100)
x = 16 * np.sin(t)**3
y = 13 * np.cos(t) - 5 * np.cos(2*t) - 2*np.cos(3*t) - np.cos(4*t)
plt.plot(x,y, 'red', linewidth=2)
plt.fill_between(x, y, color = 'red', alpha = 0.2)


Here is the outcome:



Continue reading...