The Si(x)-function (integral of the sine) in Python requires the usage of the scipy-package!
import scipy from scipy.special import* (si,ci) = sici(X)
Now si and ci hold the results of the sine / cosine integral.
Make sure not to confuse the Si(x)-function with si(x) = sin(x)/x = sinc(x), the cardinal sine function. Especially German literatur often uses the expression si(x) instead of sinc(x).