[PyQt] processEvents on QlistWidget operations does nothing

[P. Mathé]

Thank you Mark for your suggestion, I will write a test program to check it.
Nevertheless, be aware that if I replace the "urllib.urlopen(next_url).read()" statement
by a 'time.sleep(2)" statement the behaviour is the same.
I will let you know the result of my test.
Pierre
Le lundi 28 janvier 2008, vous avez écrit :
> On 2008-01-28, P. Mathé wrote:
> > Thank you guys for all the interest you have in my little problem (that in
> > fact I consider as a Qt bug or design flaw).
> 
> I'm coming late to this thread, so please excuse me if I've
> misunderstood, but I don't think the problem is a Qt bug or flaw.
> 
> I think the problem is that you are trying to mix a Python networking
> library (urllib) with a GUI. The former blocks and the latter should not
> be blocked.
> 
> One solution is to use PyQt's networking library instead since it does
> not block. So the outline of a solution would be something like this:
> 
>     # start each download here
>     def extraire(self):
> 	# ...
> 	for jour in jours:
> 	    ftp = QFtp(self) # or QHttp
> 	    # set up the network connection
> 	    ftplist.append(ftp) # ftplist = [] in __init__
> 	    self.connect(ftp,
> 		    SIGNAL("dataTransferProgress(qint64,qint64)"),
> 		    lambda: self.showProgress(ftp))
> 	    self.connect(ftp, SIGNAL("done(bool)"), self.handleDone)
> 
>     # show progress here
>     def showProgress(self, ftp, done, total):
> 	# update the QProgressBar
> 
>     # do any "after downloading complete" processing here
>     def handleDone(self, error):
> 	    
> This is all untested pseudo-code. The point I'm making is that there are
> two approaches to networking that I think work well with PyQt: (1) use
> PyQt's networking classes and signals/slots to monitor progress, (2) use
> a separate thread for networking as others have suggested. Oh, and I
> guess there's a third approach: use Twisted---I believe that that
> library has hooks so that it fits nicely into Qt's event loop.
> 
> >
> > Le dimanche 27 janvier 2008, Andreas Pakulat a écrit :
> > > On 27.01.08 13:36:37, Scott Aron Bloom wrote:
> > > > > Its not about replacing 1 line of code, its about properly designing
> > > > > your applications business logic. Moving heavy work into a thread is
> > > >
> > > > the
> > > >
> > > > > right thing to do (or separate process). QApplication::processEvents
> > > >
> > > > is
> > > >
> > > > > the ugly hack for those who are not able to use threads properly.
> > > > >
> > > > > Andreas
> > > >
> > > > But... adding 1 item to a list view.. is not heavy work.. And neigher
> > > > does it appear that the creation of the complete list of items...
> > >
> > > Right, but thats not what the code actually does and I also suspect that
> > > adding the item is still done in the main thread.
> > >
> > > > If the code was actually downloading the content of each URL... then I
> > > > would put it in a thread..
> > >
> > > Thats exactly what the urllib-call (notice the read() at the end of that
> > > line) does, it opens the url and reads the whole file.
> >
> > Yes I download an url page. But this is not what I call a heavy work, this
> > is the opposite as the processor spend most of is time waiting for the web
> > server to answer
> >
> > > And I suspect
> > > that this is the part that got moved into a separate thread. Now maybe
> > > I've just seen far worse code, but a short QThread::run() that iterates
> > > over urls, downloads them and then emits a signal for each with whatever
> > > content is needed doesn't look ugly to me.
> >
> > This is not so simple because the emit signal must be emitted from an
> > object created in a non GUI thread context: it adds an indirection to the
> > stuff. Here is the modified program that works (I have changed 
> > p=urllib.urlopen(next_url).read() for  time.sleep(2) for tests reasons).
> > Corrections to make it better designed are welcomed, but I am still
> > convinced that the original one was better. (remember that I do not want
> > the QApplication.processEvents in it : QListWidget.addItem should work
> > normally without it)
> >
> > > Andreas
> >
> > _______________________________________________
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> 
> 
>