[PyQt] Python properties on virtual methods

[Alessandro Pasotti]

2015-04-21 17:20 GMT+02:00 Phil Thompson <phil at riverbankcomputing.com>:

> On 21/04/2015 4:12 pm, Alessandro Pasotti wrote:
>
>> Hi,
>>
>> I noticed that if I create a property() alias on a virtual method, the
>> alias will always call the base class method instead of the concrete
>> instance method.
>>
>> Is this the expected behaviour?
>> Is it documented somewhere?
>>
>> Here using PyQt4 4.8.5 and python 2.7, SIP should be 4.15.5
>>
>
> A simple, complete example that demonstrates the problem would help.
>


Hi Phil,

I know an example would help but a simple one is not possible: I'm working
on a QT app embedded in a python plugin embedded in a 10K sloc C++ app.

But, I try.

instance "d" is a QgsPostgresProvider : public QgsVectorDataProvider
https://github.com/elpaso/QGIS/blob/master/src/providers/postgres/qgspostgresprovider.h
which is a subclass of QgsVectorDataProvider
https://github.com/elpaso/QGIS/blob/master/src/core/qgsvectordataprovider.h
API Docs: http://qgis.org/api/qgsvectordataprovider_8h_source.html


In [70]: d = l.dataProvider()


In [71]: d

Out[71]: <qgis._core.QgsVectorDataProvider at 0x7f132375fb00>


In [72]: d.capabilities?

Docstring: QgsVectorDataProvider.capabilities() -> int

Type: builtin_function_or_method


In [73]: d.capabilities()

Out[73]: 115615


In [74]: d.__class__.capabilities2 = property(d.__class__.capabilities)


In [75]: d.capabilities2?

Type: property

String form: <property object at 0x7f1322ac6470>

Docstring: QgsVectorDataProvider.capabilities() -> int



In [76]: d.capabilities2

Out[76]: 0


The problem is that instruction 73 calls
QgsPostgresProvider::capabilities() while instruction 76 calls
QgsVectorDataProvider::capabilities()
https://github.com/elpaso/QGIS/blob/master/src/core/qgsvectordataprovider.cpp#L107
and returns 0 (NO CAPABILITIES).

Am I doing something wrong?

-- 
Alessandro Pasotti
w3:   www.itopen.it
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