old_contents: class School(object):
      def __init__(self):
          pass
  
new_contents: from collections import defaultdict
  
  
  class School(object):
      def __init__(self, schoolname):
          self.schoolname = schoolname
          self._grades = defaultdict(set)
  
      def grade(self, n):
          return self._grades[n]
  
      def add(self, name, grade):
          self._grades[grade].update({name})
  
      def sort(self):
          return [(g, tuple(sorted(self._grades[g])))
                  for g in sorted(self._grades)]
  
subject: Add initial solution