old_contents: from __future__ import unicode_literals
  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):
          times = sorted(
              set(itertools.chain(*self.slots_qs().values_list("start", "end")))
          )
          slots = Slot.objects.filter(pk__in=self.slots_qs().values("pk"))
          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)
      next(b)
      return itertools.zip_longest(a, b)
  
new_contents: from __future__ import unicode_literals
  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):
          times = sorted(
              set(itertools.chain(*self.slots_qs().values_list("start", "end")))
          )
          slots = Slot.objects.filter(pk__in=self.slots_qs().values("pk"))
          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)
      # https://www.python.org/dev/peps/pep-0479/
      # https://stackoverflow.com/a/51701040/113527
      try:
          next(b)
      except StopIteration:
          pass
      return itertools.zip_longest(a, b)
  
subject: Handle StopIteration exceptions.