[PyQt] Re: SIP bug with object lifetime

[Giovanni Bajo]

On 13/05/2007 12.41, Phil Thompson wrote:

>> Hi Phil,
>>
>> I've got another bug with object lifetimes:
>>
>> =========================================
>> from qt import *
>> import weakref
>>
>> app = QApplication([])
>>
>> ql = QListView(None)
>> viewport = ql.viewport()
>>
>> o = QObject(viewport)
>> o.xxx = viewport  # bug-trigger!
>>
>> destroyed = []
>> def cb(wr):
>>      destroyed.append(1)
>> wr = weakref.ref(o, cb)
>>
>> del o
>> del viewport
>> assert not destroyed, "object destroyed too early #1!"
>>
>> import gc
>> gc.collect()
>> assert not destroyed, "object destroyed too early #2!"
>>
>> del ql
>> import gc
>> gc.collect()
>> assert destroyed, "object never destroyed!"
>> =========================================
>> Traceback (most recent call last):
>>    File "pyqtbug19.py", line 25, in ?
>>      assert not destroyed, "object destroyed too early #2!"
>> AssertionError: object destroyed too early #2!
>>
>>
>> This happens with latest PyQt and SIP official releases (3.17.1 and
>> 4.6). The line that seems to trigger the bug is the one marked with a
>> comment.
> 
> This behaves as I would expect - ie. it's a missing feature rather than a bug.
> 
> Although ql is the parent of viewport, Python doesn't know that and there is 
> no hidden extra reference to viewport to keep it alive when collect() is run.

But the problem here is that "o" is collected. o is a QObject whose lifetime 
should be transferred to C++ (given that it has a non-NULL parent, right?).

And why is this behaviour triggered *only* when I add the "xxx" attribute to 
o? If I don't do that, everything looks right.
-- 
Giovanni Bajo