Mailman 3 March 2003 - Twisted

[Twisted-Python] Confusing traceback from mktap.py
by Bradley Duane Peters March 12, 2003

March 12, 2003

Greetings, I have somehow caused my Twisted application to become un-TAPable. Running it through mktap.py (in the same fashion as when it did work) results in the following traceback. Traceback (most recent call last): File "mktap.py", line 30, in ? run() File "C:\Python22\Lib\site-packages\twisted\scripts\mktap.py", line 178, in run a.save() File "C:\Python22\Lib\site-packages\twisted\internet\app.py", line 634, in save dumpFunc(self, f) File "C:\Python22\… [View More]

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[Twisted-Python] newbie adbapi question
by Martin Waite March 11, 2003

March 11, 2003

Hi, I'm making some progress on my application, but there are a few ugly looking things in here and I wonder if I'm doing them right: 1) one theme (I would have said thread, but I'm not using threads) of execution requires that 3 database queries are executed one after the other. My current solution involves chaining calls to adbapi.operation() and adbapi.query() together. My first query updates a table and so calls adbapi.operation(). In the callback to this, I make … [View More]

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[Twisted-Python] Portland Perspective Broker presentation Monday
by Kevin Turner March 11, 2003

March 11, 2003

This coming Monday (March 10th), I will be addressing the Portland Python Interest Group on the subject of Twisted's Perspective Broker. Topics will include a few words on security, an example of how to implement a Observer/Observable system across the network, and whatever else I dream up between now and Monday. You can take this as a free prelude to Brian Warner's more extensive treatment of the topic later this month at PyCon, or Glyph's many hour tutorial (pending confirmation) at OSCON … [View More]

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[Twisted-Python] Re: [Twisted-commits] Updated defer.html so that the first 4 examples are runnable, split the 3rd
by Andrew Bennetts March 11, 2003

March 11, 2003

On Sat, Mar 08, 2003 at 04:44:56PM -0600, cce CVS wrote: > Modified files: > Twisted/doc/howto/defer.html 1.29 1.30 [..snip..] > @@ -19,14 +19,22 @@ > methods where the common idiom is to block until a result is > gotten.</p> > <pre class="python"> > + > class Getter: > > def getData(self, x): > - self.blockUntilResult(x) > - return result > + return self.someBlockingCall(x) > + > + def someBlockingCall(… [View More]self,x) > + print "blocking" > + import time > + time.sleep(4) > + return x * 3 > > g = Getter() > print g.getData(3) > +print "blocking" > + > </pre> Why does this code snippet now do 'print "blocking"' twice? > <h3>Don't Call Us, We'll Call You</h3> > @@ -39,29 +47,43 @@ > understand the necessity for Deferreds.</p> > > <pre class="python"> > + > class Getter: > > def getData(self, x, callback): > - self.callback = callback > - # this call does not block, it ensure self.gotResult is called > - # when we have the result > - self.onResult(x, self.gotResult) > - > - def gotResult(self, result): > - self.callback(result) > + self.callback = callback; self.x = x Why not two seperate lines here? > + self.nonBlockingOperation() > + # > + # Timer class happens to wrap the previous code in > + # a thread; but this could be any asyncronous operation > + # such as selecting from a socket, etc. > + # > + from threading import Timer > + t = Timer(4, self.gotResult) > + t.start() > + > + def nonBlockingOperation(self): > + print "non-blocking" > + > + def gotResult(self): > + self.callback(3*self.x) > > def gotData(d): > print d > > g = Getter() > g.getData(3, gotData) > + > </pre> You've sacrificed clarity for runnability. I'm not sure that's the right thing to do; the point of this example is now obscured behind details like how threading.Timer works, and spelling out a dummy "nonBlockingOperation" method where before it was quite clear without it. Not all example code in the Howtos must be immediately executable standalone... I think perhaps this example code would be better in the doc/examples directory, where it is more appropriate for examples to be verbose like this. Also, the way the example used to be reflected an idiomatic use in Twisted: where there is some event handler, e.g. onResult, fired at an arbitrary time by some external source. Think of e.g. Protocol objects with dataReceived. The example as it was emphasised that Deferreds can apply equally well when you don't have control over when some event completes -- regardless of whether it came from a thread, or the network, or anywhere. > > -<p>There are several things missing in this simple example. There is no way to > -know if the data never comes back; no mechanism for handling errors. There is > -no way to distinguish between different calls to gotData from different > -sessions. <code>Deferred</code> solves these problems, by creating a single, > -unified way to defer execution of code that depends on blocking calls.</p> > +<p>There are several things missing in this simple example. There is no way > +to know if the data never comes back; no mechanism for handling errors. The > +example does not handle a multiple callback functions, nor does it give a > +method to merge arguments before and after execution. Further, there is no > +way to distinguish between different calls to gotData from different > +producer objects. <code>Deferred</code> solves these problems, by creating > +a single, unified way to handle callbacks and errors from deferred > +execution.</p> What does "merge arguments before and after execution" mean to a Twisted newbie? Why would they want to do it? > > <h2>Deferreds</h2> > > @@ -69,9 +91,45 @@ > a function will at some point have a result. We can attach callback functions > to a Deferred, and once it gets a result these callbacks will be called. In > addition Deferreds allow the developer to register a callback for an error, > -with the default behavior of logging the error. This is an asynchronous > -equivalent of the common idiom of blocking until a result is returned or an > -exception it raised.</p> > +with the default behavior of logging the error. The deferred mechanism > +standardizes the application programmer's interface with all sorts of > +blocking or delayed operations.</p> That probably should be "*D*eferred", not "deferred". I think I'd also like to add back the comment about "This is an asynchronous equivalent of ..." -- perhaps it's overly jargonistic, but it is the way I think about Deferreds; they are the primary tool Twisted provides to abstract away blocking operations into a fundamentally asynchronous framework. > @@ -82,39 +140,48 @@ > to return the result to the HTTP client.</p> > > <pre class="python"> [..snip..] > </pre> Again, with the next two examples I think you've obscured the point in your efforts to make everything explicit. I'd rather have a 10 line example that illustrates a concept, than a 20 line example that obscures the same concept behind irrelevant method definitions, etc. On the other hand, I think long examples, say 50 lines or more, should be runnable, because anything long enough to require that many lines to explain probably should be ready for a newbie to play with. Informally, I'd say this is the different between <pre class="python"> and <a href=... class="py-listing"> -- when you're listing a file, it *should* be a complete, runnable example. In fact, complete, runnable examples probably should be a listing for the reader's convenience, i.e. put the code in doc/listings somewhere, rather that in the .html file. Please don't be discouraged from working on the docs! They *do* need work... I just happen to think that defer.html is probably the doc least in need of improvement :) -Andrew. [View Less]

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[Twisted-Python] www.twistedmatrix.com down
by Gerhard Häring March 11, 2003

March 11, 2003

At the moment I recommend to somebody on c.l.py to check out Twisted, and verify if I typed the URL correctly, I can't connect to the HTTP port :-( The host is not completely down, as I can connect to www.twistedmatrix.com:smtp. <sarcasm> Speaking of which, I remember seeing the Twisted web server advertised as "enterprise-ready" here ... </sarcasm> -- Gerhard

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[Twisted-Python] SMTPClient
by Anders Hammarquist March 10, 2003

March 10, 2003

Hi gang, I found a small bug in dealing with error messages from the SMTP server. Here's the revised patch to take care of this. /Anders

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[Twisted-Python] gzip with web
by William Dode March 10, 2003

March 10, 2003

hi, I convert a cgi site in twisted. On the server, the script run 10x faster ! but my users doesn't understand why i'm so happy since the see the page less quickly... I think it's because apache use mod_gzip. How can i send the content with gzip ? bye -- William Dode - http://flibuste.net

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[Twisted-Python] Re: [Twisted-commits] minor code cleaup
by Itamar Shtull-Trauring March 10, 2003

March 10, 2003

Hi, I don't like these changes to defer.html. They give the message that you only use Deferreds with threads - this is not true, and very misleading...

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[Twisted-Python] slap bandaid on shoutcast
by Jaakko Niemi March 9, 2003

March 9, 2003

--- shoutcast.py 2003-03-09 16:17:01.000000000 +0200 +++ shoutcast.py.working 2003-03-09 16:16:04.000000000 +0200 @@ -32,6 +32,7 @@ self.path = path self.metamode = "mp3" self.databuffer = "" + self.metaint = "" def connectionMade(self): self.sendCommand("GET", self.path)

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[Twisted-Python] updated defer.html in cvs
by Clark C. Evans March 9, 2003

March 9, 2003

Hello. I updated defer.html in CVS so that it has runnable examples. Also, in the first couple paragarphs it wasn't clear that Deferred actually doesn't defer execution, but rather is a callback/errback handler mechanism. So, I edited a small chunk of prose to help reflect that. {this particular point threw me for a loop on my first reading when I was a newbie} Anyway, I put a snapshot of the file on my site: http://clarkevans.com/defer.html it doesn't have any of the images, … [View More]

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