[PySide] Bug is worse - please ignore

[Christian Tismer]

Nathan,

I tried my example again today and have to admit that I can't
reproduce the problem, myself.

I had too many windows open last night and was misled.

properties are ok, they don't create a reference (sigh, good)
and I was messing up, because of my reduced vision.

Sorry about this.

cheers - chris


On 30.11.12 03:43, Nathan Smith wrote:
> I am very interested in this because I have a PySide application where 
> my widgets don't die gracefully (and destroyed isn't signalling their 
> death).  I use properties heavily in my code, so I was excited when I 
> saw your email thinking they were the culprit.  However, I just tried 
> your example using Python 2.7.1 and PySide 1.1.1, and I can't 
> reproduce the problem.  My table prints "destroyed" immediately when I 
> call del m.  Are you sure that "property" creates a reference?
>
> I did verify in my environment that onDestroy must be static to 
> function correctly.
>
>
> On Thu, Nov 29, 2012 at 4:40 PM, Christian Tismer 
> <tismer at stackless.com <mailto:tismer at stackless.com>> wrote:
>
>     Hi friends,
>
>     On 11/29/12 6:37 PM, Stephan Deibel wrote:
>     > Alexey Vihorev wrote:
>     >> Thanks, nice find, but... I hit the next hurdle trying to go this
>     >> way. The signal QObject.destroyed(obj) is passing no arguments
>     >> (probably because obj is already destroyed), so my static
>     method has
>     >> nothing to work on. Which kind of devaluates the whole idea, IMHO.
>     >> And in PyQt4 it*does* pass the object. Even more: in PyQt4 there is
>     >> no need for static method approach, as it works perfectly with
>     >> instance methods:
>     >
>     > Yea, you would have to bind the necessary data to the callback
>     like this:
>     >
>     >   def on_destroy(val1=self.whatever, val2=self.something):
>     >     print 'destroyed'
>     >   self.destroyed.connect(on_destroy)
>     >
>     > Whether this is possible or useful in your case is of course
>     going to
>     > depend on the details of the code.
>     >
>     > Having 'destroyed' be emitted before the object is destroyed and
>     > getting the object reference as an arg makes more sense to me.
>     That is
>     > what PyQt seems to do and it is what QObject does under Qt using
>     C++,
>     > so I'd call this a bug in PySide.  I've added
>     > https://bugreports.qt-project.org/browse/PYSIDE-129
>
>     This bug is only half of the story:
>
>     We had that simple @staticmethod work-around.
>     But actually, the main reason seems to be that PySide suffers
>     any reference cycle.
>
>     The tiny example again breaks as soon as I add a property:
>
>     {code}
>          from PySide.QtCore import QAbstractTableModel, QObject
>
>          class MyModel(QAbstractTableModel):
>              def __init__(self, *args):
>                  super(MyModel, self).__init__(*args)
>                  self.destroyed.connect(self.onDestroy)
>
>              @staticmethod
>              def onDestroy():
>                  print('destroyed')
>
>              @property
>              def hugo(self):
>                  return 42
>
>          m = MyModel()
>          del m
>     {code}
>
>     Remove the @property, and it works, again.
>
>     Rule of thumb:
>     If you need anything like a property, use a normal Python class
>     and put your Qt object into it as an attribute. Otherwise your
>     program will tend to grow in memory ;-)
>
>     Stefan, I added this code to your bug report.
>
>     cheers - chris
>
>     --
>     Christian Tismer             :^)   <mailto:tismer at stackless.com
>     <mailto:tismer at stackless.com>>
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-- 
Christian Tismer             :^)   <mailto:tismer at stackless.com>
Software Consulting          :     Have a break! Take a ride on Python's
Karl-Liebknecht-Str. 121     :    *Starship* http://starship.python.net/
14482 Potsdam                :     PGP key -> http://pgp.uni-mainz.de
phone +49 173 24 18 776  fax +49 (30) 700143-0023
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