old_contents: """Return ordered groups of lessons."""
  
  from collections import OrderedDict
  from topics.models import (
      AgeGroup,
      LessonNumber,
  )
  
  
  def group_lessons_by_age(lessons):
      """Return ordered groups of lessons.
  
      Lessons are grouped by the lesson minimum age and maximum ages,
      and then order by number.
  
      Args:
          lessons: QuerySet of Lesson objects (QuerySet).
  
      Returns:
          A ordered dictionary of grouped lessons.
          The key is a tuple of the minimum age and maximum ages for
          the lessons.
          The value for a key is a sorted list of lessons (ordered by number).
      """
      grouped_lessons = OrderedDict()
      for age_group in AgeGroup.objects.distinct():
          for lesson in age_group.lessons.filter(id__in=lessons).order_by("lessonnumber"):
              lesson.number = LessonNumber.objects.get(lesson=lesson, age_group=age_group).number
              if age_group in grouped_lessons.keys():
                  grouped_lessons[age_group].append(lesson)
              else:
                  grouped_lessons[age_group] = [lesson]
      return grouped_lessons
  
new_contents: """Return ordered groups of lessons."""
  
  from collections import OrderedDict
  from topics.models import (
      AgeGroup,
      LessonNumber,
  )
  
  
  def group_lessons_by_age(lessons):
      """Return ordered groups of lessons.
  
      Lessons are grouped by the lesson minimum age and maximum ages,
      and then order by number.
  
      Args:
          lessons: QuerySet of Lesson objects (QuerySet).
  
      Returns:
          A ordered dictionary of grouped lessons.
          The key is a tuple of the minimum age and maximum ages for
          the lessons.
          The value for a key is a sorted list of lessons (ordered by number).
      """
      grouped_lessons = OrderedDict()
      for age_group in AgeGroup.objects.distinct():
          for lesson in age_group.lessons.filter(id__in=lessons).order_by("lessonnumber"):
              lesson.number = LessonNumber.objects.get(lesson=lesson, age_group=age_group).number
              if age_group in grouped_lessons.keys():
                  grouped_lessons[ages].add(lesson)
              else:
                  grouped_lessons[ages] = set([lesson])
      return grouped_lessons
  
subject: Fix bug where lessons are duplicated across age groups.