%pylab inline

Populating the interactive namespace from numpy and matplotlib

import matplotlib.pyplot as plt
centre=(0.5,0.5)
width=1.0
plt.figure(figsize=(20,20))
fig = plt.gcf()
for i in xrange(1,50):    
    square=plt.Rectangle((0.5-width/2,0.5-width/2),width,width,color='k')
    radius=width/2
    circle=plt.Circle(centre,radius,color='w')
    width=2*(np.sqrt(radius*radius/2))
    fig.gca().add_artist(square)
    fig.gca().add_artist(circle)
plt.show()