Mailman 3 January 2009 - Twisted

Re: [Twisted-Python] Perspective broker and inlineCallbacks exception handling problem
by Terry Jones 06 Jan '09

06 Jan '09

Hi Maik I'm not an expert on inlineCallbacks, but I know enough to give something of an answer. > I am developing a basic client/server application based on twisted. > For communication purposes I am using perspective broker. I have > problems with inlineCallbacks and remotely raised errors: > > My client code looks like this (pseudo code): > > class Client: > @defer.inlineCallbacks > def login(self, prms): > self.factory = pb.PBClientFactory() > reactor.connect(host, port) > self.perspective = yield self.factory.login() > self.services = yield self.perspective.callRemote('getClientServices') > > When using this class in application, I want to handle errors raised remotely: > > @defer.inlineCallbacks > def main(): > client = Client() > try: > yield client.login(prms) > except Exception, e: > print 'Handled exception:', e > > However, no matter what is raised on remote side, except block is > never used. The first thing to say is that you shouldn't send us pseudo code. It will help you understand what's going on if you write a small example and play with it. And that will help us help you because we'll be able to see exactly what's going on and run your code ourselves. Without a real example, it's hard to give a concrete answer. There are quite a few subtleties involved in using inlineCallbacks, and you're using it twice. Below is some working code that has something like the calling pattern you seem to be trying to set up. If I cause _login to raise an exception, it IS propagated all the way back to the except Exception clause. > But if I change the code to plain except, exception is handled: > > @defer.inlineCallbacks > def main(): > client = Client() > try: > client.login(prms) > except: > print 'Some error occurred' Note that in the above snippet, you're using inlineCallbacks but you're not yielding anything. If you try calling this main() function, it will give you an exception: Failure instance: Traceback: <type 'exceptions.AttributeError'>: 'NoneType' object has no attribute 'send' That's just an example of the subtleties (and it's not so sublte in this case), and underlines why you should send us real code. Are you actually trying to call main()? > If I rewrite this function using classic deferred style, it works as > excepted (prints error with the correct type): > > def eb_failure(failure): > print type(failure), failure > > def cb_success(result): > print 'OK', result > > def main(): > client = Client() > d = client.login(prms) > d.addCallbacks(cb_success, eb_failure) Right. But that code is very different from what's going on behind the scenes when you use inlineCallbacks. > I am purposely raising errors derived from pb.Error. Using the > inlineCallbacks version I can only inspect remote errors with > sys.exc_info(), and that results in a plain string object, which > includes the classname of the original error like > 'myerror.MyAuthenticationError' How do you raise the error? Let's see the code. > What am I doing wrong? Is there a way to resolve this? Sure. But we need to know more first. Below is some code that might be useful. It's also worth trying to figure out how inlineCallbacks does its magic. Terry --- #!/usr/bin/python from twisted.internet import defer, reactor def _login(d): try: hello except Exception: d.errback() else: d.callback(True) def login(): d = defer.Deferred() reactor.callLater(1, _login, d) return d class Client: @defer.inlineCallbacks def login(self, prms): yield login() @defer.inlineCallbacks def main(): client = Client() try: yield client.login(33) except Exception, e: print 'Handled exception:', e def ok(result): print "ok", result def nok(failure): print "nok", failure def stop(_): reactor.stop() def go(): x = main() x.addCallback(ok) x.addErrback(nok) x.addBoth(stop) if __name__ == '__main__': reactor.callLater(0, go) reactor.run()

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Re: [Twisted-Python] Looping
by Terry Jones 06 Jan '09

06 Jan '09

>>>>> "Robert" == Robert Hancock <hancock.robert(a)gmail.com> writes: Robert> I want to put this into a loop and run it as a daemon, but the Robert> looping is causing me a problem. I've tried making the above into Robert> a procedure (minus the stop working call back and reactor.run()) Robert> and it does not run. Any suggestions on how to encapsulate this Robert> into loop would be gratefully appreciated. It's hard to help unless you post more of your code or are more specific. What do you mean "the looping is causing me a problem"? How many urls are in url_tuples? Is there a reason why you're using just one deferred? Also why not use client.downloadPage to put the contents into files? Terry

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[Twisted-Python] Perspective broker and inlineCallbacks exception handling problem
by Maik Friedmann 05 Jan '09

05 Jan '09

Hello, I am developing a basic client/server application based on twisted. For communication purposes I am using perspective broker. I have problems with inlineCallbacks and remotely raised errors: My client code looks like this (pseudo code): class Client: @defer.inlineCallbacks def login(self, prms): self.factory = pb.PBClientFactory() reactor.connect(host, port) self.perspective = yield self.factory.login() self.services = yield self.perspective.callRemote('getClientServices') When using this class in application, I want to handle errors raised remotely: @defer.inlineCallbacks def main(): client = Client() try: yield client.login(prms) except Exception, e: print 'Handled exception:', e However, no matter what is raised on remote side, except block is never used. But if I change the code to plain except, exception is handled: @defer.inlineCallbacks def main(): client = Client() try: client.login(prms) except: print 'Some error occurred' If I rewrite this function using classic deferred style, it works as excepted (prints error with the correct type): def eb_failure(failure): print type(failure), failure def cb_success(result): print 'OK', result def main(): client = Client() d = client.login(prms) d.addCallbacks(cb_success, eb_failure) I am purposely raising errors derived from pb.Error. Using the inlineCallbacks version I can only inspect remote errors with sys.exc_info(), and that results in a plain string object, which includes the classname of the original error like 'myerror.MyAuthenticationError' What am I doing wrong? Is there a way to resolve this? Regards, Maik

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[Twisted-Python] Looping
by Robert Hancock 05 Jan '09

05 Jan '09

I have a process that takes a list of URLs, uses client.getPage() to retrieve the data, writes the contents to disk, and then moves the file to another directory. # get feed list - this is a list tuples # url, name, username, password url_tuples = feed_list(feed_file) global C_URLS d = defer.succeed(log_start(log)) for tup_url in url_tuples: C_URLS += 1 d.addCallback(get_page, tup_url) d.addErrback(get_page_error, tup_url[0]) d.addCallback(page_to_file, tup_url) d.addErrback(page_to_file_error) d.addCallback(file_to_rsync_queue) d.addErrback(file_to_rsync_queue) d.addCallback(stop_working) #d.addErrback(self.gotError, (feed[0], 'while stopping')) reactor.run() I want to put this into a loop and run it as a daemon, but the looping is causing me a problem. I've tried making the above into a procedure (minus the stop working call back and reactor.run()) and it does not run. Any suggestions on how to encapsulate this into loop would be gratefully appreciated.

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[Twisted-Python] Weekly Bug Summary
by exarkun＠twistedmatrix.com 04 Jan '09

04 Jan '09

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[Twisted-Python] ssh v1 support
by Deniz Pecel 03 Jan '09

03 Jan '09

Hi List Does twisted support ssh v1? thanks

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