Re: [Twisted-Python] help with Deferreds

Yes, I was expecting you to wrap item.obsolete() and renew(data) in try/except, as needed. If you want a clean but slightly slower way to do that, how about something like:

def getCachedResult(cache, key):

def release(result, item): item.release() return result

def renew(data): return renew(data)

def notFound(fail): fail.trap(NotFound)

def readItem(item): return item.read()

def checkObsolete(item): d = defer.maybeDeferred(item.obsolete) d.addCallback(lambda _: readItem(item)) d.addBoth(release, item) d.addCallback(renew) return d

d = cache.open(key) d.addCallbacks(checkObsolete, notFound) return d

Thanks, maybeDeferred is what I missed :)