import numpy as np
import matplotlib.pyplot as plt

x, y = np.ogrid[-2:4:1024j, -1.5:1.5:768j]

r = x + 1j * y
z = 0.4

for g in range(100):
    print('Iteration number: ', g)
    z = z ** 2 + r

threshold = 256
mask = np.abs(z) < threshold

plt.imshow(mask.T, extent=[-2, 4, -1.5, 1.5])
plt.gray()
plt.show()