1  class stack:
2      def __init__(self):
3           self.items = list()
4      #---------------------------
5      def push(self, nodePtr):
6          self.items.append(nodePtr)
7      #------------------------
8      def pop(self):
9          return self.items.pop()
10     #--------------------------
11     def top(self):
12         return self.items[0]