Python中值过期的容器

Question

我在找一个线程安全的Python容器，这个容器里的值会在一段时间后自动被删除。有没有这样的类呢？

Answer 1

也许你想要一个LRU缓存。这里有一个我一直想试试的：

http://pypi.python.org/pypi/repoze.lru

看起来这个缓存是线程安全的。

Answer 2

这就是我现在想要的差不多的东西：

from datetime import datetime, timedelta
from collections import deque

class ExpireCounter:
    """Tracks how many events were added in the preceding time period
    """

    def __init__(self, timeout=timedelta(seconds=1)):
        self.timeout = timeout
        self.events = deque()

    def add(self):
        """Add event time
        """
        self.events.append(datetime.now())

    def __len__(self):
        """Return number of active events
        """
        self.expire()
        return len(self.events)

    def expire(self):
        """Remove any expired events
        """
        now = datetime.now()
        try:
            while self.events[0] + self.timeout < now:
                self.events.popleft()
        except IndexError:
            pass # no more events


if __name__ == '__main__':
    import time
    c = ExpireCounter()
    assert(len(c) == 0)
    c.inc()
    time.sleep(0.75)
    c.inc()
    assert(len(c) == 2)
    time.sleep(0.75)
    assert(len(c) == 1)

Answer 3

这里是一个线程安全的 ExpireCounter 版本：

import datetime
import collections
import threading

class ExpireCounter:
    """Tracks how many events were added in the preceding time period
    """

    def __init__(self, timeout=1):
        self.lock=threading.Lock()        
        self.timeout = timeout
        self.events = collections.deque()

    def add(self,item):
        """Add event time
        """
        with self.lock:
            self.events.append(item)
            threading.Timer(self.timeout,self.expire).start()

    def __len__(self):
        """Return number of active events
        """
        with self.lock:
            return len(self.events)

    def expire(self):
        """Remove any expired events
        """
        with self.lock:
            self.events.popleft()

    def __str__(self):
        with self.lock:
            return str(self.events)

可以这样使用：

import time
c = ExpireCounter()
assert(len(c) == 0)
print(c)
# deque([])

c.add(datetime.datetime.now())
time.sleep(0.75)
c.add(datetime.datetime.now())    
assert(len(c) == 2)
print(c)
# deque([datetime.datetime(2010, 11, 19, 8, 50, 0, 91426), datetime.datetime(2010, 11, 19, 8, 50, 0, 842715)])

time.sleep(0.75)
assert(len(c) == 1)
print(c)
# deque([datetime.datetime(2010, 11, 19, 8, 50, 0, 842715)])