defsim_distance(prefs,person1,person2): si={} for item in prefs[person1]: if item in prefs[person2]: si[item]=1
if len(si)==0:return0 sum_of_squares=sum([pow(prefs[person1][item]-prefs[person2][item],2) for item in prefs[person1] if item in prefs[person2]]) return1/(1+sqrt(sum_of_squares))