new_contents: class Stack(object):
      """Implementation of Stack ADT"""
  
      def __init__(self, items):
          self.items = items
  
      def is_empty(self):
          return self.items == []
  
      def push(self, item):
          self.items.appends(item)
  
      def pop(self):
          return self.items.pop()
  
      def peek(self):
          return self.items[len(self.items) - 1]
  
      def size(self):
          return len(self.items)
  
subject: Implement Stack ADT