Queue.py

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

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

 def dequeue(self):
 if not self.length():
 raise QueueEmptyException()
 item = self.__items[0]
 self.__items = self.__items[1:]
 return item

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


class QueueEmptyException(Exception):
 pass