old_contents: class Course:
      def __init__(self, code, credit, instructor):
          self.code = code
          self.credit = credit
          self.instructor = instructor
  
      def __eq__(self, other):
          if other == None:
              return False
  
          return self.code == other.code and \
                 self.credit == other.credit
  
      def __str__(self):
          return str(self.code) + " " + str(self.credit) + " " + str(self.instructor)
new_contents: class Course:
      def __init__(self, code, credit, instructor):
          self.code = code
          self.credit = credit
          self.instructor = instructor
  
      def __eq__(self, other):
          if other == None:
              return False
  
          return self.code == other.code and \
                 self.credit == other.credit
  
      def __str__(self):
          return self.code
subject: Revert string method for course