Re: [Twisted-Python] tee method in twisted.internet.defer.py ?
"JP" == exarkun <exarkun@twistedmatrix.com> writes: JP> We implemented this 5 or 6 times at Divmod.
I'm not surprised. Given that I'd have thought it would've made it into defer.py at some point. JP> The most recent incarnation looks like this: JP> http://divmod.org/trac/browser/trunk/Epsilon/epsilon/pending.py Thanks. That's more of a radial / hub pattern. I'm dealing with the case of already having a deferred around and wanting to tee off it without interfering with its callback/errback chain. E.g., I have a class that's already passed a deferred back to its caller, and I later need to arrange to do some more stuff when the deferred fires. The caller of my class may in the meantime have added callbacks to the deferred, I tee off it with no effect on my original caller. That's just one example use. I'm sure you'll have implemented something for similar situations, too. JP> Not to say it's a bad idea, but I don't think it's _obviously_ a great JP> idea. If someone wanted to contribute a documented, tested JP> implementation, particularly with examples of common patterns that it JP> simplifies, then you could probably convince someone to commit it. I don't need it committed, I was just wondering why something like that doesn't already exist. Re patterns: it would be great to have a series of diagrams illustrating situations one might want to deal with and showing how these can be done with Deferred code. Your Epsilon class could be shown as a hub with new listeners arriving, ready for the triggering of the callback. The tee diagram would show a T (or multiple Ts on the same callback chain) in the obvious way. add{Callback,Errback} is like a normal UNIX pipe and, stretching things a little, chainDeferred reminds me a bit of UNIX exec (though with real differences). There's a PyCon talk in there somewhere. Like Patterns of Asynchronous Flow of Control using Twisted Deferreds. It often feels to me like there's a lurking taxonomy of Deferred use cases or building blocks that's just waiting for someone to come along and make really clear to the world. I'd really love to do it, but I just don't have the time. Terry
participants (2)
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Kevin Horn -
Terry Jones