[PyQt] QVariant bug(?)

[Arve Knudsen]

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