Queue with a linked list

LinkedListQueue.py

class EmptyQueueException(Exception):
    pass

class LinkedListQueueNode:
    def __init__(self, data):
        self._next = None
        self._data = data

    def set_next(self, n):
        self._next = n

    def get_next(self):
        return self._next

    def get_data(self):
        return self._data

class LinkedListQueue:

    def __init__(self):
        self._front = None
        self._end = None

    def enqueue(self, data):
        new_node = LinkedListQueueNode(data)

        if self._front == None:
            self._front = self._end = new_node
        else:
            self._end.set_next(new_node)

    def dequeue(self):
        
        if self._front == None:
            raise EmptyQueueException, "Queue is empty"
        else:
            value = self._front.get_data()
            self._front = self._front.get_next()
            
            return value

    def front(self):

        if self._front == None:
            raise EmptyQueueException, "Queue is empty"
        else:
            return self._front.get_data()

    def is_empty(self):
        
        return self._front == None

    def max(self):

        if self._front == None:
            raise EmptyQueueException, "Queue is empty"
        else:
            m = self._front.get_data()
            node = self._front.get_next()
            while node != None:
                if m < node.get_data():
                    m = node.get_data

            return m