[PyQt] QPyNullVariant

[Phil Thompson]

On Fri, 13 Jul 2012 15:49:48 +0200, Rodolfo Zitellini <xhero.gm at gmail.com>
wrote:
> On Thu, Jul 12, 2012 at 11:44 PM, Phil Thompson
> <phil at riverbankcomputing.com> wrote:
>> On Thu, 12 Jul 2012 21:08:11 +0200, Rodolfo Zitellini
>> <xhero.gm at gmail.com>
>> wrote:
>>> Hi All,
>>> I'm trying to run a pyqt software (frescobaldi,
>>> http://frescobaldi.org/) in macos using macports. I have macports
>>> 2.1.1 on macosx 10.7.4, xcode 4.3.2 (qt 4.8.2, pyqt 4.9.1, sip 4.13.2,
>>> for completeness).
>>>
>>> My problem, it seems, is that object will never be null but only
>>> QPyNullVariant. Eg.:
>>>
>>> language = QSettings().value("language", "")
>>> if language:
>>>    #do stuff
>>> else
>>>   #fallback
>>>
>>> language is never null: it is either the correct class or
>>> QPyNullVariant (instead of null!), so it always tests true.
>>> I'm asking this here in this list since with the old qt for mac 4.7 it
>>> worked. I also tried the same software on linux, with qt 4.8.1 and
>>> same pyqt/sip, and it works as is should (i.e. null and not
>>> QPyNullVariant).
>>>
>>> I initially suspected it could be a compilation configuration option,
>>> but I could not find anything. Anyone han an idea of what I can be
>>> doing wrong?
>>
>> I don't know what you mean by null in this context, but ...
>>
>>
http://www.riverbankcomputing.com/static/Docs/PyQt4/html/incompatibilities.html#pyqt-v4-9-2
>>
>> ...may help.
>>
>> Phil
> 
> Thanks Phil!
> what bugs me most is that Frescobaldi on linux works perfectly, on
> macos (same pyhon and lib versions) it crashes on startup:
> 
> <PyQt4.QtCore.QPyNullVariant object at 0x10f581980>
> Traceback (most recent call last):
>   File "frescobaldi", line 3, in <module>
>     import frescobaldi_app.main
>   File "/Users/xhero/devel/frescobaldi-git/frescobaldi_app/main.py",
> line 41, in <module>
>     import po.setup         # Setup language
>   File "/Users/xhero/devel/frescobaldi-git/frescobaldi_app/po/setup.py",
> line 74, in <module>
>     setup()
>   File "/Users/xhero/devel/frescobaldi-git/frescobaldi_app/po/setup.py",
> line 64, in setup
>     mo = find(language)
>   File
"/Users/xhero/devel/frescobaldi-git/frescobaldi_app/po/__init__.py",
> line 41, in find
>     filename = os.path.join(podir, language + ".mo")
> TypeError: unsupported operand type(s) for +: 'QPyNullVariant' and 'str'
> 
> The offending code is in setup.py, when it reads the language:
>     language = QSettings().value("language", "")
>     print language
>     if not language:
>         try:
>             language = locale.getdefaultlocale()[0]
>         except ValueError:
>             pass
>     if not language:
>         language = "C"
>     return language
> 
> in linux, language prints None, on osx it prints QPyNullVariant. it
> will then evaluate False in "if not language" and then crash when it
> arrives in __init__.py.
> 
> This used to work with qt 4.7 on osx. Just upgrading to 4.8 breaks
> everything.
> Any ideas?

It would suggest that there is a null QVariant stored in the settings for
"language". If there was no value stored then "" would be returned. A
workaround would therefore be to update or delete the settings data either
manually or with a little script.

Phil