code: def _cook_slots(period, increment):
      
      tdiff = datetime.timedelta(minutes=increment)
      num = int((period.end - period.start).total_seconds()) // int(tdiff.total_seconds())
      s = period.start
      slots = []
      for i in range(num):
          sl = period.get_time_slot(s, s + tdiff)
          slots.append(sl)
          s = s + tdiff
      return slots
docs: Prepare slots to be displayed on the left hand side
          calculate dimensions (in px) for each slot.
          Arguments:
          period - time period for the whole series
          increment - slot size in minutes