[Twisted-Python] Consistent interfaces to asynchronous partially-available services using Deferreds and state machines (was Re: Another approach to allowing __init__ to work with Deferreds)

[Tristan Seligmann]

On Tue, May 12, 2009 at 1:39 PM, Terry Jones <terry at jon.es> wrote:
> If Python allowed me to return a deferred from __init__, my problem would
> vanish.  That's not going to happen though, I know :-)

Well, if you /really/ want to, you can implement that; something like:

####
from twisted.internet import defer

class DeferredClass(object):
    def __new__(cls, *a, **kw):
        inst = super(DeferredClass, cls).__new__(cls, *a, **kw)
        return defer.maybeDeferred(inst.__init__, *a,
**kw).addCallback(lambda ign: inst)
####

Example usage:

####
class Example(DeferredClass):
    def __init__(self, value):
        def _cb(value):
            self.value = value
        return defer.succeed(value).addCallback(_cb)

def _printIt(x):
    print x.value

Example(42).addCallback(_printIt)  # Prints "42"
####

Of course, this doesn't implement your magic wrapping behaviour, so
maybe that's not what you meant.
-- 
mithrandi, i Ainil en-Balandor, a faer Ambar