code: def frequent_users(self):
          
          key = "eighthactivity_{}:frequent_users".format(self.id)
          cached = cache.get(key)
          if cached:
              return cached
          freq_users = self.eighthscheduledactivity_set.exclude(eighthsignup_set__user=None).exclude(administrative=True).exclude(special=True).exclude(
              restricted=True).values('eighthsignup_set__user').annotate(count=Count('eighthsignup_set__user')).filter(
                  count__gte=settings.SIMILAR_THRESHOLD).order_by('-count')
          cache.set(key, freq_users, timeout=60 * 60 * 24 * 7)
          return freq_users
docs: Return a QuerySet of user id's and counts that have signed up for this activity more than
          `settings.SIMILAR_THRESHOLD` times. This is be used for suggesting activities to users.