import pylab as plt
import numpy as np

x = np.arange(0.0, 2, 0.01)
y1 = np.sin(2 * np.pi * x)
y2 = 0.8 * np.sin(4 * np.pi * x)

fig, (ax1, ax2, ax3) = plt.subplots(
  3, 1, sharex=True, figsize=(6, 6))

ax1.fill_between(x, y1)
ax1.set_title('fill between y1 and 0')

ax2.fill_between(x, y1, 1)
ax2.set_title('fill between y1 and 1')

ax3.fill_between(x, y1, y2)
ax3.set_title('fill between y1 and y2')
ax3.set_xlabel('x')
fig.tight_layout()

import pylab as plt
import numpy as np

X = np.linspace(0, 3, 200)
Y1 = X**2 + 3
Y2 = np.sin(X)
Y3 = np.cos(X)

plt.plot(X, Y1, lw=4)
plt.plot(X, Y2, lw=4)
plt.plot(X, Y3, lw=4)

plt.fill_between(X, Y1, Y2, color='k', alpha=.5)
plt.fill_between(X, Y1, Y3, color='y', alpha=.5)

plt.show()

import matplotlib.pyplot as plt


x = [1, 2, 1, 0]
y = [2, 1, 0, 1]

plt.fill(x, y)
plt.show()