[PySide] RuntimeError: Failed to connect signal xxxx

Stefan Champailler schampailler at skynet.be
Sat Feb 23 10:50:02 CET 2013


I have never seen that kind of issue but what I've learned the hard
way is that memory leaks can cause very erratic behaviours.
So, as a first step, if you didn't already do so, you should make
sure there are no ownership issues in your code. If you have a large
code base, I found it was easier to simply remove the code part
by part until the problem disappear (and so had I a better idea of
the location of the issue).

I also found very instructing to reduce the code to a small piece
to reproduce the bug. Doing so help to learn quite a bit about PySide
(because when you reduce code to a minimum you get to know how to
express some ideas in a much better way).

Either way, I bet you have some work ahead...


On 02/21/2013 10:22 PM, Joel B. Mohler wrote:
> On 2/21/2013 12:52 PM, Zak wrote:
>> The following idea helped me with a different glitch that was 
>> probably unrelated to yours, but who knows, it might help you. Try 
>> each of the following:
>> # Signals and slots example
>> # From qt_webview_play.py
>> @Slot(bool)  # bool is PySide.QtCore.bool
>> def my_slot(input_bool):
>>     pass
>> # The following three lines should be equivalent, but they
>> # are not always equivalent in practice:
>> q_widget.connect(q_widget, SIGNAL("toggled(bool)"), my_slot)
>> q_widget.toggled.connect(my_slot)
>> q_widget.toggled[bool].connect(my_slot)
>> I don't know why they are different, but sometimes they are. My bug 
>> arose when I tried to manually disconnect and reconnect signals, 
>> specifically the loadFinished(bool) signal on a QWebView widget.
>> In my own experience, it is best to always use the first method, with 
>> SIGNAL("toggled(bool)"). I notice that the StackOverflow question you 
>> linked uses the third method. Try switching it up and see if anything 
>> helps.
> Thanks for your comments.  I think they were helpful, but the bug 
> reproduction process here got pretty weird as I fiddle with this some 
> more.  I commonly use method 2 to connect signals and slots (I wasn't 
> aware of method 3, but I think I see it's necessity at times).  I 
> changed the one connection to use method 1 and sure enough I think I 
> don't get that failure any more.
> (and now just a personal tale of woe this has led me down ...) 
> However, I now see that regardless of signal/slot issues, that if I 
> sit here and open,close,reopen and repeat continuously I'm sure to get 
> signal/slot failures and missing attributes and even segfault crashes 
> sometime in the first 30 open/close iterations. Unfortunately, this 
> widget that I'm closing and reopening has nested sub-widgets probably 
> 4 layers deep and many many nuances. It will take a while to decode 
> this, but it certainly looks like memory corruption.  I'm not going to 
> hazard a guess about where to point a finger at this point aside to 
> say that pure python pyside shouldn't segfault.
> For the record ... I'm on win 7 32 bit; PySide 1.1.2; python 2.7.3; Qt 
> 4.8.2.
> Joel
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Timeo Danaos et dona ferentes

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