[QUESTION] Implements a pure virtual class in python calls pure virtual function

[jjcasmar]

I am trying to implement a virtual class i have in C++ using Python. To do that, I am using the trampoline as described in pybind documentation. The issue here is that in python, I need to keep the python object around or I would have a pure virtual function call error.

My python class looks like this

class BlendingField(PyVNCS.Sim2D.BlendingField):
    def __init__(self):
        PyVNCS.Sim2D.BlendingField.__init__(self)

    def blending(self, point):
        return 0.5

And I have to use like this

blendingField = BlendingField()
simCreator.blendingField = blendingField

simCreator.create()

Basically, I create the BlendingField with the python implementation, I assign it to simCreator.blendingField property and I call simCreator.create(), which is a C++ function using the blending field.

If instead of doing it like that, I do it like this

simCreator.blendingField = BlendingField()

simCreator.create()

I get a crash when trying to use the blending field from C++. This happens because the python object is destroyed.

Is this the expected behavior? I find it kind of confusing and it needs an extra line which most of the times you dont really want.

[virtuald]

Duplicate of #1120, #1145, #1333, #1389, #1552, #1546, #1566, #1774, #1902, #1937

Fixed in #2839, hopefully will be decided on/merged soon.