[PyQt] Segfault when trying newDoc.setDocumentLayout(QtGui.QPlainTextDocumentLayout(newDoc))

[GT6]

Phil Thompson wrote:
> On Mon, 02 Feb 2009 13:49:23 +0100, GT6 <gt6 at gmx.net> wrote:
>   
>> Phil Thompson wrote:
>>     
>>> On Mon, 02 Feb 2009 03:37:13 +0100, GT6 <gt6 at gmx.net> wrote:
>>>   
>>>       
>>>> Hi there.
>>>>
>>>> When running the below sample script, and clicking the button, it will
>>>> segfault, and I don't understand why or how. I've overwritten a
>>>>         
> function
>   
>>>> in QPlainTextEdit and it should create a new document, set the
>>>> PlainTextDocumentLayout and then set the document on the QPlainTextEdit
>>>> widget. The important part is this (1st way):
>>>>
>>>>         newDoc = QtGui.QTextDocument()
>>>>        
>>>>         
> newDoc.setDocumentLayout(QtGui.QPlainTextDocumentLayout(newDoc))
>   
>>>>         self.setDocument(newDoc)
>>>>
>>>> The above segfaults. I also tried this (2nd way):
>>>>
>>>>             newDoc = QtGui.QTextDocument()
>>>>             newDoc.setDocumentLayout(self.documentLayout())
>>>>             self.setDocument(newDoc)
>>>>
>>>> This one doesn't segfault, but I get this error:
>>>>
>>>> AttributeError: documentLayout
>>>>
>>>> Apart from that, I tried this third option (3rd way):
>>>>
>>>>         newDoc = QtGui.QTextDocument()
>>>>
>>>>
>>>>         
> newDoc.setDocumentLayout(QtGui.QPlainTextDocumentLayout.__init__(newDoc))
>   
>>>>         self.setDocument(newDoc)
>>>>
>>>> with the only difference from the first one being that __init__ is
>>>> called explicitly instead of expecting it to be defaultet. This one
>>>> _doesn't_ segfault, but gives this error:
>>>>
>>>> QPlainTextEdit::setDocument: Document set does not support
>>>> QPlainTextDocumentLayout
>>>>
>>>> Which makes no sense as not calling __init__ directly shouldn't be any
>>>> different than calling it explicitly.
>>>>     
>>>>         
>>> __init__() initialises a class, it doesn't create one.
>>>
>>>   
>>>       
>>>> So, does anyone have any idea why
>>>> this is happening? Do you have a bug tracker?
>>>>     
>>>>         
>>> Keep a reference to "newDoc" - it is getting garbage collected too soon.
>>>
>>> Phil
>>>
>>>   
>>>       
>> Thanks for your help.
>>
>> Well, that only works once. So I replace the plzsegfault function in the 
>> sample with this (full sample binned here
>>     
> http://rafb.net/p/P6sqML59.html):
>   
>>     def plzsegfault(self):
>>         self.newDoc = QtGui.QTextDocument()
>>         
>>
>>     
> self.newDoc.setDocumentLayout(QtGui.QPlainTextDocumentLayout(self.newDoc)) 
>   
>> # First way
>>         self.setDocument(self.newDoc)
>>
>> Then, I can safely click the button once, and it also does what I expect 
>> it to do, but clicking the button a second time will again segfault.
>> What I'm trying to do is that clicking the button will clear the 
>> textfield and make a new document and display it. Do I really have to 
>> care about the document names? I *could* implement a counter and have 
>> all the documents have different names but I don't really need those 
>> specific names in the future. I just need the textfield to discard the 
>> old one and get a new one, everytime the button is clicked. The only 
>> reference to the document that I use lateron is self.document(). I don't 
>> need the name...
>>     
>
> You might not but Python needs a reference of some sort to stop the object
> being garbage collected.
>
> Your new version is still garbage collecting too soon. Just add the
> following to the end of plzsegfault() in your *original* version...
>
>     self._doc = newDoc
>
> Phil
>
>   
It's still not working in my "real" application. I've been trying to 
figure out what's wrong for hours now but it's just weird and I don't 
understand it. Here's the complete code of what I'm doing. It's a small 
calendar: http://rafb.net/p/rW8qrv26.html

The code is a bit messy, there are some obsolete things in there. In any 
case, could you please try the following:

1.) run the script
2.) type something in a day field
3.) click >>
4.) click <<
5.) Segfault!

But on the other hand:

1.) run the script
2.) click >>
3.) click <<
4.) type something in a day field
7.) No more segfaults. You can type anything anywhere and click >> << at 
any point and everything works asa exepected.

So for some reason, doing >> << before touching any of the fields 
prevents the subsequent segfault, while typing something in a day field 
right away results in a segfault. And I just don't understand why.

The script is made up from PyQalMain which is the main widget with all 
the stuff and TextEditEnter which overwrites a few functions of 
QPlainTextEdit and has the goFuture and goPast functions added. All the 
day field contecnts are saved in PyQalMain.dayDict {} (line 131) which 
is passed to all 7 day fields as an argument.

I'd be so glad if someone would find out what's wrong here...

Thanks,
Carl.








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