old_contents: '''
  Implementation of Stack data structure
  
  '''
  
  
  class Stack:
  
      def __init__(self):
  	'''
  	Initialize stack
  
  	'''
  	self.items = []
  
  
      def is_empty(self):
  	'''
  	Return True if stack if empty else False
  	
  	'''
  	return self.item == []
  
  
      def push(self, item):
  	'''
  	Push item to stack
  
  	'''
  	self.items.append(item)
  
  
      def pop(self):
  	'''
  	Pop item from stack
  
  	'''
  	return self.items.pop()
  
  
      def peek(self):
  	'''
  	Return value of item on top of stack
  
  	'''
  	return self.items[-1]
  
      
      def size(self):
  	'''
  	Return number of items in stack
  
  	'''
  	return len(self.items)
  
new_contents: '''
  Implementation of Stack data structure
  
  '''
  
  
  class Stack(object):
  
      def __init__(self):
  	'''
  	Initialize stack
  
  	'''
  	self.items = []
  
  
      def is_empty(self):
  	'''
  	Return True if stack if empty else False
  	
  	'''
  	return self.item == []
  
  
      def push(self, item):
  	'''
  	Push item to stack
  
  	'''
  	self.items.append(item)
  
  
      def pop(self):
  	'''
  	Pop item from stack
  
  	'''
  	return self.items.pop()
  
  
      def peek(self):
  	'''
  	Return value of item on top of stack
  
  	'''
  	return self.items[-1]
  
      
      def size(self):
  	'''
  	Return number of items in stack
  
  	'''
  	return len(self.items)
  
subject: Convert old-style class to new-style class