[Twisted-Python] maybeDeferred capability

mardiros mardiros at laposte.net
Fri Oct 16 04:01:11 EDT 2009

As I am still a new user of Twisted,
I have decide to use the maybeDeferred capability.

The real aim is to cache sql queries,
but I have written this example from 
the twisted mayneDeferred doc.

I am happy with my code, but, I would like
to share it to have some feed back

Here it is:

import types
from datetime import datetime, timedelta

from twisted.internet import defer
from twisted.internet import reactor, task

class asyncmemoize:
def __init__(self, function,pool_time=10,cachelifetime=10):
self.function = function
self._cache = {}
self._cachelifetime = timedelta(0,cachelifetime)
self._cleaner = task.LoopingCall(self.cleanCache)
self._cleanrun = False

def __call__(self, *args, **kwargs):
key = (tuple(args), frozenset(kwargs.items()))

if key not in self._cache:
f = self.function(*args, **kwargs).addCallback(self.callback,key)
self._cache[key]=[datetime.today(), f]

print "from cache"
return self._cache[key][1]

def callback(self,result,key):
print "Put real value in cache"
self._cache[key]=[datetime.today(), self._cachelifetime, result]
return result

def cleanCache(self):
if not self._cleanrun:
self._cleanrun = True
print 'Clean the cache...'
#log.msg('Clean the persistent cache...', logLevel=logging.DEBUG)
expire = datetime.today()
i = 0
for k,v in self._cache.items():
print v[0], "<", expire, "=>", v[0] > expire 
if v[0] < expire:
del self._cache[k]
print '%i items removed' % i
#log.msg('%i items removed' % i, logLevel=logging.DEBUG)
self._cleanrun = False

def saveInCache(result,key):
print "saving to cache"
cache[key] = result
return result

def asynchronousIsValidUser(user):
print "Loading is authenticating from async"
d = defer.Deferred()
reactor.callLater(2, d.callback, user in ["Alice", "Angus", "Agnes"])
return d

def synchronousIsValidUser(user):
Return true if user is a valid user, false otherwise
return user in ["Alice", "Angus", "Agnes"]

def printResult(result,user):
if result:
print "User", user ,"is authenticated"
print "User", user ,"is not authenticated"

def authenticateUser(isValidUser, user):
print "Authenticating user ", user
d = defer.maybeDeferred(isValidUser, user)
return d.addCallback(printResult,user)






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