在Python中丢弃具有最大容量的FIFO队列？

Question

我需要一个丢弃FIFO队列，它会在项目满了时自动丢弃。它不必是线程安全的。效率更重要。

也就是说，我需要从设备中采样信号，同时能够在半随机时间检索最后的 n 秒（对象）。

我自己实现了一个（不那么线程安全）缓冲区，但我觉得我在这里重新发明了这个轮子。另外我们每秒都在讨论100个物体。大多数将被丢弃，例如必须一次检索3000（= 30秒的数据）（比如每十分钟一次）。

Python标准库或其他地方是否已经存在这样的类？我使用了一些goggle-fu但没有找到任何有用的东西。

DiscardingBuffer

from Queue import Queue, Full, Empty
import logging


class DiscardingBuffer():
    def __init__(self, capacity=0):
        self._queue = Queue(maxsize=capacity)

    def put(self, item):
        while True:
            try:
                self._queue.put(item, block=False)
                logging.debug('Put item: {0}'.format(item))
                break
            except Full:
                discarded_item = self._queue.get(block=False)
                logging.debug('Buffer is full. Discarding: {0}'.format(discarded_item))

    def flush(self):
        items = []

        while True:
            try:
                items.append(self._queue.get(block=False))
            except Empty:
                logging.debug('Buffer is now empty.')
                break

        return items


def main():
    buf = DiscardingBuffer(5)

    for i in xrange(10):
        buf.put(i)

    logging.debug('Remaining items: {0}'.format(buf.flush()))
    logging.debug('Verify it is empty: {0}'.format(buf.flush()))


if __name__ == '__main__':
    logging.basicConfig(level=logging.DEBUG,
                        format='[%(levelname)1.1s %(asctime)s %(name)s (%(process)d):%(lineno)d] %(message)s',
                        datefmt='%Y-%m-%d %H:%M:%S')
    main()

输出

[D 2013-08-22 10:13:58 root (4164):13] Put item: 0
[D 2013-08-22 10:13:58 root (4164):13] Put item: 1
[D 2013-08-22 10:13:58 root (4164):13] Put item: 2
[D 2013-08-22 10:13:58 root (4164):13] Put item: 3
[D 2013-08-22 10:13:58 root (4164):13] Put item: 4
[D 2013-08-22 10:13:58 root (4164):17] Buffer is full. Discarding: 0
[D 2013-08-22 10:13:58 root (4164):13] Put item: 5
[D 2013-08-22 10:13:58 root (4164):17] Buffer is full. Discarding: 1
[D 2013-08-22 10:13:58 root (4164):13] Put item: 6
[D 2013-08-22 10:13:58 root (4164):17] Buffer is full. Discarding: 2
[D 2013-08-22 10:13:58 root (4164):13] Put item: 7
[D 2013-08-22 10:13:58 root (4164):17] Buffer is full. Discarding: 3
[D 2013-08-22 10:13:58 root (4164):13] Put item: 8
[D 2013-08-22 10:13:58 root (4164):17] Buffer is full. Discarding: 4
[D 2013-08-22 10:13:58 root (4164):13] Put item: 9
[D 2013-08-22 10:13:58 root (4164):26] Buffer is now empty.
[D 2013-08-22 10:13:58 root (4164):38] Remaining items: [5, 6, 7, 8, 9]
[D 2013-08-22 10:13:58 root (4164):26] Buffer is now empty.
[D 2013-08-22 10:13:58 root (4164):39] Verify it is empty: []

Answer 1

使用collections.deque指定maxlen，

>>> q = deque(maxlen=2)
>>> q.extend([1, 2, 3])
>>> q
deque([2, 3], maxlen=2)