[PyKDE] List confusion

Phil Thompson phil at riverbankcomputing.co.uk
Wed Sep 24 09:48:01 BST 2003

On Wednesday 24 September 2003 8:02 am, Derek Fountain wrote:
> This might be a general Python newbie question. But it's confusing me in a
> PyQt context. :o)
> I have a slot in a class which receives a list of images. It adds that list
> to it's existing list, then sends off a signal saying the existing list has
> changed:
>     currentImageList = []
>     def slotInsertImages( self, imageList ):
>         self.currentImageList.extend( imageList )
>         self.emit( PYSIGNAL("signalUpdateImageList"), self.currentImageList
> )
> This doesn't work. I get an error saying:
> TypeError: Argument 2 of QObject.emit() has an invalid type
> Changing the "self.currentImageList" to "(self.currentImageList,)" makes it
> work.
> On the other end of that signal is a slot which looks like this:
>     def slotUpdateImageList( self, imageList ):
>         print "update image list"
>         for file in imageList:
>             print file
> Which also works. :o)
> What I don't understand is why I need to force the currentImageList into a
> tuple with one item - that item being my list of image names. What is
> received at the other end is clearly a list since I can loop over it. It
> feels like the slot should have to take the first index of its 'imageList'
> argument, but that's clearly not the case.
> What's going on? What does the self.emit() method actually do with it's
> second argument?

Interprets it as an argument list (so it has to be a tuple) and calls the slot 
with those arguments. An example with two arguments might make it clearer...

  self.emit( PYSIGNAL("signalUpdateImageList"), (self.currentImageList, flag))

  def slotUpdateImageList( self, imageList, flag ):

Should emit() take a variable number of arguments rather than a single tuple? 
Maybe, but it's too late to change now.


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