Multiple inheritance for QGraphicsItem

[Maurizio Berti]

As we all know, PyQt doesn't allow multiple inheritance of more Qt classes,
except when explicitly allowed (eg. QTextObjectInterface).

When using the Graphics View framework, though, it is sometimes useful to
have a QGraphicsItem subclass that also provides QObject features: for
example, a QGraphicsRectItem that emits a signal whenever its geometry
changes.

Right now, whenever I need something similar, I normally choose one of the
following options, depending on my needs and code simplicity:

- create a dummy QObject subclass and use an instance of it as a member of
the actual QGraphicsItem one, then eventually emit its signals whenever
necessary;
- create a dummy QGraphicsObject subclass as the actual one to be used,
with the "real" items as its children, then implementing boundingRect()
(possibly returning childrenBoundingRect()) and a no-op paint(), and
eventually "copying" the actual child item common functions by proper
implementation, simple monkey patching or even __getattr__ override;

While both solutions "work", they are not really acceptable, nor robust or
reliable:

- the dummy QObject "proxy" is an unnecessary difficulty that complicates
access to the actual signal source; using Qt properties is a further
complication (consider the case of using QPropertyAnimation);
- the "main QGraphicsObject" approach adds complexity and further
difficulties in geometry/transform management and access to the actually
intended item;
- issues with the lifespan of the QObject and the "real" QGraphicsItem,
including connected signals (eg. using QTimers or animations);

Qt actually considers and allows such multiple inheritance (it's the very
nature of QGraphicsObject).

So, my question is quite simple: would it be possible to allow proper
multiple inheritance for QGraphicsItem+QObject?
Therefore, would that implicitly allow multiple inheritance for all
QGraphicsItem inherited classes (the standard ones and those created in
Python, including mixins)?

Thanks,
MaurizioB

-- 
È difficile avere una convinzione precisa quando si parla delle ragioni del
cuore. - "Sostiene Pereira", Antonio Tabucchi
http://www.jidesk.net
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