old_contents: import itertools
  import operator
  
  from django.db.models import Count, Min
  
  from symposion.schedule.models import Room, Slot, SlotRoom
  
  
  class TimeTable(object):
      
      def __init__(self, day):
          self.day = day
      
      def slots_qs(self):
          qs = Slot.objects.all()
          qs = qs.filter(day=self.day)
          return qs
      
      def rooms(self):
          qs = Room.objects.all()
          qs = qs.filter(schedule=self.day.schedule)
          qs = qs.filter(pk__in=SlotRoom.objects.filter(slot__in=self.slots_qs().values("pk")).values("room"))
          qs = qs.order_by("order")
          return qs
      
      def __iter__(self):
          slots = self.slots_qs().all()
          times = sorted(set(itertools.chain(*slots.values_list("start", "end"))))
          slots = slots.annotate(room_count=Count("slotroom"), order=Min("slotroom__room__order"))
          slots = slots.order_by("start", "order")
          row = []
          for time, next_time in pairwise(times):
              row = {"time": time, "slots": []}
              for slot in slots:
                  if slot.start == time:
                      slot.rowspan = TimeTable.rowspan(times, slot.start, slot.end)
                      slot.colspan = slot.room_count
                      row["slots"].append(slot)
              if row["slots"] or next_time is None:
                  yield row
      
      @staticmethod
      def rowspan(times, start, end):
          return times.index(end) - times.index(start)
  
  
  def pairwise(iterable):
      a, b = itertools.tee(iterable)
      b.next()
      return itertools.izip_longest(a, b)
  
new_contents: import itertools
  
  from django.db.models import Count, Min
  
  from symposion.schedule.models import Room, Slot, SlotRoom
  
  
  class TimeTable(object):
      
      def __init__(self, day):
          self.day = day
      
      def slots_qs(self):
          qs = Slot.objects.all()
          qs = qs.filter(day=self.day)
          return qs
      
      def rooms(self):
          qs = Room.objects.all()
          qs = qs.filter(schedule=self.day.schedule)
          qs = qs.filter(pk__in=SlotRoom.objects.filter(slot__in=self.slots_qs().values("pk")).values("room"))
          qs = qs.order_by("order")
          return qs
      
      def __iter__(self):
          slots = self.slots_qs().all()
          times = sorted(set(itertools.chain(*slots.values_list("start", "end"))))
          slots = slots.annotate(room_count=Count("slotroom"), order=Min("slotroom__room__order"))
          slots = slots.order_by("start", "order")
          row = []
          for time, next_time in pairwise(times):
              row = {"time": time, "slots": []}
              for slot in slots:
                  if slot.start == time:
                      slot.rowspan = TimeTable.rowspan(times, slot.start, slot.end)
                      slot.colspan = slot.room_count
                      row["slots"].append(slot)
              if row["slots"] or next_time is None:
                  yield row
      
      @staticmethod
      def rowspan(times, start, end):
          return times.index(end) - times.index(start)
  
  
  def pairwise(iterable):
      a, b = itertools.tee(iterable)
      b.next()
      return itertools.izip_longest(a, b)
  
subject: Remove unused import