new_contents: class MyClass(object):
  
      class_attr = 'foo'
  
      def __init__(self, val):
          self.inst_attr = val
  
  
  
  
  a = MyClass(1)
  b = MyClass(2)
  
  print a.inst_attr
  ?
  print b.inst_attr
  ?
  
  print a.class_attr == b.class_attr
  ?
  print a.class_attr is b.class_attr
  ?
  
  b.class_attr = 4
  
  print a.class_attr
  ?
  
subject: add code for exercise about class attr