contenitore in cui i valori scadono in python

Question

Sono in un contenitore Python sicuro da file in cui i valori vengono automaticamente rimossi dopo un certo tempo. Esiste una classe del genere?

Answer 1

Ecco una versione thread-safe di ExpireCounter:

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) 

che può essere utilizzato in questo modo:

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)]) 

Answer 2

Forse si desidera una cache LRU. Ecco quello che ho in mente di provare:

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

Sembra essere thread-safe.

Answer 3

Questo è più o meno quello che voglio per ora:

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)