Stack.py

class Stack:
 """
 This is a simple implementation of Stack
 """
 pass

 def __init__(self):
 self.__items = []

 def push(self, item):
 self.__items.append(item)

 def pop(self):
 if not self.is_empty():
 return self.__items.pop()
 raise StackEmptyException('stack is empty')

 def length(self):
 return len(self.__items)

 def is_empty(self):
 if not len(self.__items):
 return True
 return False


class StackEmptyException(Exception):
 pass