The confidence sort algorithm is implemented in _sorts.pyx, I have rewritten their Pyrex implementation into pure Python (do also note that I have removed their caching optimization)

Reddits_Algorithm.py

#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 #1.0 = 85%, 1.6 = 95%
    phat = float(ups) / n
    return sqrt(phat+z*z/(2*n)-z*((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n)

def confidence(ups, downs):
    if ups + downs == 0:
        return 0
    else:
        return _confidence(ups, downs)

quick note (little time): The sqrt should only be over the 3rd term. In your line 13, it's over all three terms. You're doing it correctly in sorts.py though.