[PyQt] QVariant bug(?)

[Arve Knudsen]

I'm getting a really mysterious segfault now, triggered by this
slightly modified case. Using the latest SIP/PyQt snapshots.

Arve

On Wed, Sep 3, 2008 at 1:43 PM, Arve Knudsen <arve.knudsen at gmail.com> wrote:
> On Wed, Sep 3, 2008 at 10:13 AM, Phil Thompson
> <phil at riverbankcomputing.com> wrote:
>> On Wed, 3 Sep 2008 08:07:25 +0200, "Arve Knudsen" <arve.knudsen at gmail.com>
>> wrote:
>>> On Tue, Sep 2, 2008 at 11:15 PM, Phil Thompson
>>> <phil at riverbankcomputing.com> wrote:
>>>> On Tue, 2 Sep 2008 22:12:54 +0200, "Arve Knudsen"
>>> <arve.knudsen at gmail.com>
>>>> wrote:
>>>>> On Tue, Sep 2, 2008 at 4:04 PM, Phil Thompson
>>>>> <phil at riverbankcomputing.com> wrote:
>>>>>> On Tue, 2 Sep 2008 11:29:00 +0200, "Arve Knudsen"
>>>>> <arve.knudsen at gmail.com>
>>>>>> wrote:
>>>>>>> I have created a simple test case which triggers a likely bug in
>>> PyQt.
>>>>>>> As the case demonstrates, I have a class template "PropertyValue"
>>>>>>> which I wrap and use with QVariant. When I run the test program
>>>>>>> ("tst.py") however, there is a segfault in the PropertyValue copy
>>>>>>> constructor. The reason as far as I've been able to tell is that PyQt
>>>>>>> doesn't register its own metatype for "StringValue"
>>>>>>> (PropertyValue<QString>), since this is already constructed for the
>>>>>>> C++ type (see qobject.sip, line 1479), with chaotic results (the C++
>>>>>>> copy constructor receives a raw PyObject for the right-hand-side
>>>>>>> argument).
>>>>>>
>>>>>> The bug should be fixed in tonight's PyQt snapshot.
>>>>>>
>>>>>> However, it leaves the question as to how you would get the instance
>>>>> back
>>>>>> out of the QVariant. QVariant.toPyObject() only handles Python objects
>>>>> at
>>>>>> the moment - not wrapped non-Qt C++ instances as you have.
>>>>>>
>>>>>> I think I need to add an optional type argument to toPyObject(), eg...
>>>>>>
>>>>>>    my_string_value = variant.toPyObject(StringValue)
>>>>>
>>>>> I don't understand what you mean here. QVariant.toPyObject currently
>>>>> works with StringValue objects?
>>>>
>>>> No, and it still won't after the bug is fixed - but there needs to be
>>> some
>>>> way to convert the C++ instance to a Python object (ie. to do the
>>> reverse
>>>> of what your test case does).
>>>
>>> Well, I'm confused, since I patched PyQt myself, and calling
>>> toPyObject() on the QVariant in my case returns the expected
>>> StringValue object.
>>
>> Obviously I can't comment on the behaviour of your patched version.
>
> All I did was mangle names of Python types, so they are distinct from
> C++ counterparts (add a PyQt-specific prefix).
>
> Arve
>
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