Segfault extending by inheritance in python

[TobiasWinchen]

This is from the examples and reproduces the bug

import crpropa
from crpropa import Mpc, nG, EeV
import numpy as np

class MySourceFeature(crpropa.SourceFeature):
    """ Set the initial energy to 10 EeV """
    def __init__(self):
        crpropa.SourceFeature.__init__(self)

    def prepareParticle(self, particleState):
        particleState.setEnergy(10 * EeV)

vgrid = crpropa.VectorGrid(crpropa.Vector3d(0), 128, 1 * Mpc)
crpropa.initTurbulence(vgrid, 1 * nG, 2 * Mpc, 5 * Mpc, -11. / 3.)
BField = crpropa.MagneticFieldGrid(vgrid)

m = crpropa.ModuleList()
m.add(crpropa.PropagationCK(BField, 1e-4, 0.1 * Mpc, 5 * Mpc))
m.add(crpropa.MaximumTrajectoryLength(25 * Mpc))

# source setup
source = crpropa.Source()
source.add(crpropa.SourcePosition(crpropa.Vector3d(0, 0, 0) * Mpc))
source.add(crpropa.SourceIsotropicEmission())
source.add(crpropa.SourceParticleType(crpropa.nucleusId(1, 1)))
source.add(crpropa.SourceEnergy(1 * EeV))
source.add(MySourceFeature())
m.run(source, 1000)

occures not always; occures in single threaded and multi threaded execution

[TobiasWinchen]

The bug also affects ObserverFeatures and Modules written in python. However,

source.add(MySourceFeature()) will fail;

sf = MySourceFeature() source.add(sf)

will work. The reason is that in the former case the object is deleted by python. See also: https://github.com/swig/swig/issues/779

Monkey patching ( https://github.com/swig/swig/issues/723) might be a solution to disown the created object first but is surely an ugly solution.

[adundovi]

It is the same issue I had almost 3 years ago, see #27 . Disown is, I agree, an ugly solution, while the one where the python is taking care of the ownership is what I regularly use and it works.

I would write a recommendation how to handle this on the wiki, section about extending CRPropa from Python, and close the issue. I'm afraid we cannot do more.

[lukasmerten]

I had this problem, too.

I agree with Andrej let's just put an explanation in the wiki and maybe a comment in the example for the source feature. So when the example is used people will know why the object has to be created outside of the class attributes.

[TobiasWinchen]

Okay, I will add a tag `Won't fix' to the bug to mark that we won't work on it, but I don't think that we should close such issues. If #27 hadn't been closed it would have saved me the time figuring out the problem.