SciPy

scipy.special.gammainc

scipy.special.gammainc(x1, x2[, out]) = <ufunc 'gammainc'>

y=gammainc(a,x) returns the incomplete gamma integral defined as 1 / gamma(a) * integral(exp(-t) * t**(a-1), t=0..x). a must be positive and x must be >= 0.