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When writing a Cython wrapper for a C++ library, I've encountered a case where it's not clear how to correctly decide when to delete certain C++ instances. The C++ library looks something like this: #include <stdio.h> #include <string.h> class Widget { char *name; public: Widget() : name(strdup("a widget")) {} ~Widget() { printf("Widget destruct\n"); } void foo() { printf("Widget::foo %s\n", this->name); } }; class Sprocket { private: Widget *important; public: Sprocket(Widget* important) : important(important) {} ~Sprocket() { important->foo(); } }; An important aspect of this library is that the Sprocket destructor uses the Widget* it was given, so the Widget must not be destroyed until after the Sprocket has been. The Cython wrapper I've written looks like this: cdef extern from "somelib.h": cdef cppclass Widget: pass cdef cppclass Sprocket: Sprocket(Widget*) cdef class PyWidget: cdef Widget *thisptr def __init__(self): self.thisptr = new Widget() def __dealloc__(self): print 'PyWidget dealloc' del self.thisptr cdef class PySprocket: cdef PyWidget widget cdef Sprocket *thisptr def __init__(self, PyWidget widget): self.widget = widget self.thisptr = new Sprocket(self.widget.thisptr) def __dealloc__(self): print 'PySprocket dealloc with widget', self.widget del self.thisptr After building the Python build like this: $ cython --cplus somelib.pyx $ g++ -I/usr/include/python2.6 -L/usr/lib somelib.cpp -shared -o somelib.so $ In the trivial case, it appears to work: $ python -c 'from somelib import PyWidget, PySprocket spr = PySprocket(PyWidget()) del spr ' PySprocket dealloc with wid

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