Mailman 3 November 2009 - Twisted

Re: [Twisted-Python] tee method in twisted.internet.defer.py ?
by Terry Jones 17 Nov '09

17 Nov '09

>>>>> "JP" == exarkun <exarkun(a)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

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[Twisted-Python] Multiple deferreds that depend on each other
by Landreville 17 Nov '09

17 Nov '09

I know people ask about deferreds all the time (and i've read through a bunch of those questions), but there is still one thing I don't quite grasp. If I want to do a number of actions in a row that each return a deferred but depend on eachother, do I need to nest those callbacks? Ie if i want to: 1. Call database function using adbabi 2. Call xmlrpc method using result from 1 3. Call database using result from 2 Would I just put 2 inside the callback for 1 and then put 3 inside the callback for 2? How would I do that in one function? All the examples I have seen have a function calling one method returning a deferred and then placing the logic (doing something with the result) in the callback, but do not deal with multiple deferreds that depend on each other.

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[Twisted-Python] tee method in twisted.internet.defer.py ?
by Terry Jones 17 Nov '09

17 Nov '09

Is there a reason why the Deferred class doesn't have a tee method like the following (untested)? def tee(self, d): def _cb(arg): d.callback(arg) return arg def _eb(arg): d.errback(arg) return arg return self.addCallbacks(_cb, _eb) I suppose it could be called teeDeferred to correspond to chainDeferred. And I guess it's clear what it does and why it's quite different from chainDeferred. I at least would find it quite useful. Terry

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[Twisted-Python] Telnet server: localecho "ON" for linux client but not for windows client
by filoufake-python＠yahoo.fr 17 Nov '09

17 Nov '09

Hello, Some month ago, exarkun helped me in the development of a very simplified telnet server. I observed that when I connect from a windows client, the LOCALECHO is set to "OFF" after the authentication. I cannot set it "ON" afterwards. Everything typed in the client console is hidden. When I use a linux client, the "ECHO" is OFF just for typing the password and then ON again. Does someone has an idea how to do with the windows client? I tried to set the ECHO ON using self.transport.will(ECHO) but that doesn't work. Here is the code: ############################################################ import sys from zope.interface import implements from twisted.internet import protocol from twisted.python import log from twisted.cred import error from twisted.cred import portal from twisted.cred import checkers from twisted.cred import credentials from twisted.conch.telnet import AuthenticatingTelnetProtocol from twisted.conch.telnet import StatefulTelnetProtocol from twisted.conch.telnet import ITelnetProtocol from twisted.conch.telnet import TelnetTransport from twisted.conch.telnet import ECHO class Realm: implements(portal.IRealm) def requestAvatar(self, avatarId, mind, *interfaces): if ITelnetProtocol in interfaces: av = MyTelnet() av.transport.will(ECHO) av.state = 'Command' return ITelnetProtocol, av, lambda:None raise NotImplementedError("Not supported by this realm") class MyTelnet(StatefulTelnetProtocol): def telnet_Command(self, line): print "line received via telnet", line self.sendLine('coucou man, you send me %s' % line) def main(): r = Realm() p = portal.Portal(r) c = checkers.InMemoryUsernamePasswordDatabaseDontUse() c.addUser("AA", "aa") p.registerChecker(c) p.registerChecker(checkers.AllowAnonymousAccess()) f = protocol.ServerFactory() f.protocol = lambda: TelnetTransport(AuthenticatingTelnetProtocol, p) log.startLogging(sys.stdout) from twisted.internet import reactor reactor.listenTCP(4738, f) reactor.run() if __name__ == '__main__': main() ############################################################ Best Regards, Philippe

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[Twisted-Python] ReverseProxy (http) using Twisted
by Fred C 17 Nov '09

17 Nov '09

I have to write a quick and dirty ReverseProxy with Twisted, for one of our internal project. I never used Twisted before, and I was wondering of someone have an handy example of a ReverseProxy with Twisted to help that I can use as bootstrap. Many thanks. Fred

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Re: [Twisted-Python] exarkun changed [#4029 - Twisted Web's wsgi.input isn't sufficiently file-like in all cases]
by Phil Christensen 17 Nov '09

17 Nov '09

-phil [sent from my phone] On Nov 16, 2009, at 4:56 PM, trac(a)twistedmatrix.com wrote: > Ticket [#4029 - Twisted Web's wsgi.input isn't sufficiently file- > like in all cases] changed by exarkun <exarkun(a)twistedmatrix.com>: > > (In [27518]) Merge wsgi-none-readline-4029 > > Author: rikyu > Reviewer: exarkun > Fixes: #4029 > Refs: #4114 > > Add a test for WSGI requests which end up with a > `tempfile.TemporaryFile` > for `Request.content` and fix the implementation to deal with this > case > by not passing `None` for the length argument to `readline` (which > temp > files do not accept, unlike StringIOs). WSGI applications can now > receive > requests with large bodies. > > --------- > status : assigned -> closed > resolution: -> fixed > --------- > http://twistedmatrix.com/trac/ticket/4029

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[Twisted-Python] Caching mechanism
by vitaly＠synapticvision.com 16 Nov '09

16 Nov '09

hi, is there any cache mechanism for twisted? Could one point me please to that docs? Thank you.

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[Twisted-Python] Weekly Bug Summary
by exarkun＠twistedmatrix.com 15 Nov '09

15 Nov '09

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[Twisted-Python] TCP Queued connections
by tim wylie 15 Nov '09

15 Nov '09

Hello, What is the best way to set up a queue of tcp connections? I'm currently using perspective broker for authentication and communication. I want the client to register with the server, and then the server send back a message telling them their place in line. This is easy, but then how can I store the connections on the server to send the client a message when it's his turn? I realize I could store IP addresses, but then you lose connections behind firewalls/etc. I could also give the client a time estimate and he could run a deferred call after that time, but I was hoping there was a more elegant way. Any thoughts? Thanks. Tim _________________________________________________________________ Hotmail: Trusted email with Microsoft's powerful SPAM protection. http://clk.atdmt.com/GBL/go/177141664/direct/01/ http://clk.atdmt.com/GBL/go/177141664/direct/01/

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[Twisted-Python] Deferred SOAP methods
by Landreville 14 Nov '09

14 Nov '09

I am making a SOAP server and all (or at least the vast majority) will be returning a deferred. The whole SOAP method is encapsulated in a deferred in most of my cases (I havent implemented this part yet.) Then I got the idea that twisted.web.soap could just wrap my SOAP method (retrieved with lookupFunction) in a deferred and return that deferred right away. For instance I would change twisted.web.soap.render where it says d = defer.maybeDeferred to d = threads.deferToThread I could also use an attribute to specify if I do not want it deferred (kinda the same way to determine whether to use keywords or not) Is this actually a good idea? I figured there might be a reason this wasn't done already considering everything in twisted is pretty well thought out.

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Twisted November 2009