[Twisted-Python] deferred folies

Federico Di Gregorio fog at initd.org
Tue Sep 30 12:27:43 EDT 2003

hi *,

lately i did some dirty Deferred tricks and i just want to know if there
is a better way to do what i did. the situation is as follows:

a server exposes through pb a "session" object. the client can call on
that object "execute" (any number of times) and then "abort" or "end" to
end the session. the session is created by calling "new_session" on the
remote perspective (after authentication, etc.)

now, for a simple get session/execute/end sequence i don't want to write
n+1 callbacks (one that waits for new_session and call execute, next one
that wait on execute and call next, etc.) so here is what I did (inside
a mixin class used in the client):

def session(self):
    return self.server.callRemote("new_session")

def execute(self, trans, *args, **kwargs)
    cb = kwargs.get('callback', None)
    if self._session:
        dfr = self.server.callRemote(trans, *args)
        if cb:
        return dfr
        dfr = self.session()
        cb = Deferred()
        dfr.addCallback(self._execute_got_session, trans, cb, *args)
        return cb

def _execute_got_session(self, session, trans, cb, *args):
    self._session = session
    return self.execute(trans, *args, callback=cb)

that is, from the client the user can just do:

d = self.execute("set-foo", 42)

and in the callback call .execute again (and be sure to be in the same
session) or call end or abort to terminate the session.

clear? mm..

what i want to know is if the "cb" trick and chainDeferred call are a
dirty hack or if that's the way they are supposed to be used and if
there is a better way to do what i do.


Federico Di Gregorio
Debian GNU/Linux Developer                                fog at debian.org
INIT.D Developer                                           fog at initd.org
   Lasciate che i furetti vengano a me. -- Maria Luisa Benedetta Panzani
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