How to enter a code block?

from pylab import plot, show, ylim, yticks
from matplotlib.numerix import sin, cos, exp, pi, arange

t = arange(0.0, 2.0, 0.01)
s1 = sin(2*pi*t)
s2 = exp(-t)
s3 = sin(2*pi*t)*exp(-t)
s4 = sin(2*pi*t)*cos(4*pi*t)

t = arange(0.0, 2.0, 0.01)
plot(t, s1, t, s2+1, t, s3+2, t, s4+3, color='k')
ylim(-1,4)
yticks(arange(4), ['S1', 'S2', 'S3', 'S4'])

show()