Simplest possible upper & lower bound plot using matplotlib

upper_lower_bound_plot.py

import matplotlib.pyplot as plt
import numpy as np

N = 100

x = np.linspace(0, 6*np.pi, N)

y = np.sin(x)

upper = y + 0.2
lower = y - 0.5

plt.plot(x, y, color = (1, 0, 0, 0.6))
plt.fill_between(x, upper, lower, color = (1, 0, 0, 0.2))

plt.xlabel(r'$\theta$', labelpad = 15)
plt.ylabel('y', labelpad = 15)
plt.show()