Slide 50
Slide 50 text
Reddit Voting Algorithm, GAE’d
def time_dependent(decay_seconds, upvotes_name, downvotes_name, created_name, score):!
"""Ranking based on both age and quality.!
!
This is the algorithm Reddit uses to sort stories. We want there to be!
churn, a constant stream of new programs hitting the hot page,!
so this algorithm takes into account both the score of the scratchpad and the age.!
See http://amix.dk/blog/post/19588!
"""!
s = getattr(score, upvotes_name) - getattr(score, downvotes_name)!
!
# Weight votes logarithmically - initial votes are worth a ton!
order = math.log(max(abs(s), 1), 10)!
!
sign = 1 if s > 0 else -1 if s < 0 else 0!
!
# Seconds since this algorithm's start date !
date = getattr(score, created_name) or datetime.datetime.now()!
seconds = epoch_seconds(date) - 1349108492!
!
return round(order + sign * seconds / decay_seconds, 7)
class TimeDependentScoreProperty(ndb.ComputedProperty):!
!
def __init__(self, decay_seconds, upvotes_name="upvotes",!
downvotes_name="downvotes", created_name="created", **kwargs):!
super(TimeDependentScoreProperty, self).__init__(functools.partial(!
time_dependent, decay_seconds, upvotes_name, downvotes_name,!
created_name), **kwargs)!