[PyQt] PyQt5 fails to handle QQuickImageProvider subclassing

[Julio César Gázquez]

Hello list. Hi Phil.

I'm dipping my toes on QML. I subclassed QQuickImageProvider in order to 
access images stored in a database from the QML side of my app.

Unfortunately, when the QML engine tries to call the provider I'm 
getting the following error:

ImageProvider supports Image type but has not implemented requestImage()

Seems this message comes from Qt's QQuickImageProvider::requestImage() 
implementation, so it's like the C++ method isn't being overridden by 
the PyQt's wrapper method.

At least the alternate QQuickImageProvider::requestPixmap() has the same 
problem.

These methods are somewhat peculiar, as they are virtual methods (and 
specifically meant to be subclassed) and have an /Out/ parameter. Doing 
a grep on the PyQt sources I see this only happens in two places outside 
this class. Maybe the wrapper for the virtual method lacks the /Out/ 
parameter?

BTW, at least another guy was bitten for this: 
http://stackoverflow.com/questions/40787663/pyqt5-qquickimageprovider-not-working.

I'm tested it on PyQt5 5.5.1, I'm not sure if it could be fixed in later 
versions.

Thanks in advance.

Greetings, Julio.