old_contents: class IntSet(object):
      def __init__(self):
          """Create an empty set of integers"""
          self.vals = []
  
      def insert(self, e):
          """Assumes e is an integer and inserts e into self"""
          if not e in self.vals:
              self.vals.append(e)
  
      def member(self, e):
          """
          Assumes e is an integer
          Returns True if e is in self, and False otherwise"""
          return e in self.vals
  
      def remove(self, e):
          """
          Assumes e is an integer and removes e from self
          Raises ValueError if e is not in self"""
          try:
              self.vals.remove(e)
          except:
              raise ValueError(str(e) + 'not found')
  
      def getMembers(self):
          """Returns a list containing the elements of self.
          Nothing can be assumed about the order of the elements"""
          return self.vals[:]
  
      def __str__(self):
          """Returns a string representation of self"""
          self.vals.sort()
          result = ''
          for e in self.vals:
              result = result + str(e) + ','
          return '{' + result[:-1] + '}' #-1 omits trailing comma
new_contents: class IntSet(object):
      def __init__(self):
          """Create an empty set of integers"""
          self.vals = []
  
      def insert(self, e):
          """Assumes e is an integer and inserts e into self"""
          if not e in self.vals:
              self.vals.append(e)
  
      def member(self, e):
          """
          Assumes e is an integer
          Returns True if e is in self, and False otherwise"""
          return e in self.vals
  
      def remove(self, e):
          """
          Assumes e is an integer and removes e from self
          Raises ValueError if e is not in self"""
          try:
              self.vals.remove(e)
          except:
              raise ValueError(str(e) + 'not found')
  
      def getMembers(self):
          """Returns a list containing the elements of self.
          Nothing can be assumed about the order of the elements"""
          return self.vals[:]
  
      def __str__(self):
          """Returns a string representation of self"""
          self.vals.sort()
          #result = ''
          #for e in self.vals:
          #    result = result + str(e) + ','
          #return '{' + result[:-1] + '}' #-1 omits trailing comma
          # or you could use
          return '{' + ','.join([str(e) for e in self.vals]) + '}'
subject: add another way of implementation of __str__()