Avoid segfault when accessing dangling Python objects

[lcpt]

The problem goes as follows:

• You put some XC nodes or elements or anything like that in a Python list node_list= [n1, n2, n3, n4]
• For whatever reason, the node n3 must be removed from the model, so the C++ counterpart of the n3 Python object is deleted. The n3 Python object and the third item of the node_list list become dangling references.
• Any attempt to access either n3 or node_list[2] results in a segmentation fault condition and the program crashes.

Maybe there is a way of informing boost.python about the deletion of the C++ objects, so n3 and node_list[2] can return None.

To look into:

• Stackoverflow related question
• boost.python how to expose...