Python implementation of the Wilson Score Interval?

Reddit uses the Wilson score interval for comment ranking, an explanation and python implementation can be found here

#Rewritten code from /r2/r2/lib/db/_sorts.pyx

from math import sqrt

def confidence(ups, downs):
    n = ups + downs

    if n == 0:
        return 0

    z = 1.0 #1.44 = 85%, 1.96 = 95%
    phat = float(ups) / n
    return ((phat + z*z/(2*n) - z * sqrt((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n))