[Twisted-Python] invoking Deferred synchronously
p.mayers at imperial.ac.uk
Tue Aug 21 06:33:55 EDT 2007
On Tue, 2007-08-21 at 05:09 -0400, Laurie Harper wrote:
> I'm sure this is trivial enough, but it has me scratching my head... I
> need to call a method that returns a Deferred, then block until the
> deferred completes (or errback's) and return the final result of the
> deferred call.
You don't want to do that.
> Specifically, something like:
> r = None, is_ok = None
> def ok(p): r, is_ok = p, True
> def fail(e): r, is_ok = e, False
> cf = pb.PBClientFactory()
> reactor.connectTCP(host, port, cf)
> d = cf.login(creds, client=self).addCallbacks(ok, fail)
> # BLOCK: wait until d has called 'ok' of 'fail'
> if is_ok:
> return r
> raise r
> If it helps, I'm trying to create a web application (using Nevow) that
> connects to another Twister service through the Persistence Broker. I'm
> trying to implement authentication, and so need a way to wait for the PB
> connection to succeed/fail so I can send the appropriate response to the
> HTTP request.
You certainly don't need to do that in a Nevow app. Just do this (I'm
assuming this is in a data or render method):
cf = pb.PBClientFactory()
reactor.connectTCP(host, port, cf)
return cf.login(creds, client=self)
Nevow will see you've returned a deferred and wait for it. Much of
Twisted will do the same. You NEVER want to "wait" for a deferred.
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