from Queue import Queue, Full

class LimitQueue(Queue):
    def put(self, item):
        while True:
            try:
                Queue.put(self, item, block=False)
            except Full:
                try:
                    self.queue.popleft()
                except Empty:
                    pass
            else:
                break


# If you want it in reverse order replace _put and _get with these:
def _put(self, item):
        self.queue.appendleft(item)
def _get(self):
        return self.queue.pop()


if __name__ == "__main__":
    q = LimitQueue(maxsize=3)

    q.put(1)
    q.put(2)
    q.put(3)
    q.put(4)
    print(q.queue)
    # Output: deque([2, 3, 4])