class QueueManager(list):
    def __init__(self, max_queue_length=3):
        self.max_queue_length = max_queue_length

        list.__init__(self)

    def isFull(self):
        return len(self) == self.max_queue_length


    def append(self, item):
        if self.isFull():
            raise IndexError, 'Maximum queue length reached.'

        if item in self:
            raise ValueError, 'This value is already listed.'

        return list.append(item)