#!/usr/bin/env python2.7 class Stack: def __init__(self): self._items = [] def push(self, item): self._items.append(item) def pop(self): return self._items.pop() def is_empty(self): return self._items == [] def peek(self): return self._items[len(self._items) - 1] def size(self): return len(self._items) if __name__ == "__main__": s = Stack() s.push(10) s.push(20) s.push([1,2,3]) print s.peek()