[PyQt] Sip and virtual functions

[Phil Thompson]

On 3 Jan 2018, at 9:53 am, Guðjón Guðjónsson <gudjon.i.gudjonsson at gmail.com> wrote:
> 
> Hi list
> 
> I have been writing a new python wrapper for the Qwt library [1,2]
> And I still have problems with virtual function definitions.
> I got the advice to add the /Abstract/ keyword to the class definitions
> and this has led to the full wrapper compiling but running with the
> following error messages:
> 
> NotImplementedError: QwtPlotHistogram.dataSize() is abstract and must be overridden
> TypeError: Qwt.QwtPlotMultiBarChart represents a C++ abstract class and cannot be instantiated

Adding /Abstract/ was probably bad advice. It is only necessary if there are additional pure virtual functions that aren't mentioned in the .sip file.  Adding /Abstract/ to a class that has pure virtual functions in the .sip file shouldn't make any difference.

> I have also been playing with setting virtual functions = 0 or not. This led to a missing
> symbols error but with the /Abstract/ keyword in the right  place this error has disappeared.
> 
> There is a patch for the Qwt c++ library on Github that instantiates the pure virtual functions
> and by using that patch my python wrapper works perfectly but the wrapper must work
> without the patch.

Is the C++ QwtPlotHistogram class abstract? If not then there must be implementations of the pure virtual functions somewhere in the class hierarchy that are missing from your .sip files.

Phil