[PySide] RuntimeError: Failed to connect signal xxxx

Joel B. Mohler jmohler at gamry.com
Thu Feb 21 22:22:42 CET 2013

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 


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