Stack using Linked List

linked-list-stack.py

"""
Implementation of a Stack (FILO) Data Structure
using a Linked List.
"""

class LinkedList(object):
  
  class __Node(object):
    def __init__(self, val):
      self.val = val
      self.next = None
    
    def __str__(self):
      return str(self.val)
      
  def __init__(self, head):
    self.head = LinkedList.__Node(head)
    self.num_items = 1
    
  def push(self, item):
    temp = self.head
    self.head = LinkedList.__Node(item)
    self.head.next = temp
    self.num_items += 1
  
  def pop(self):
    if self.is_empty():
      raise Exception("Cannot pop from empty Stack")
    
    self.head = self.head.next
    self.num_items -= 1
  
  def is_empty(self):
    return self.num_items == 0