Abraham, The idea is that I have a class Entity that contains a pointer to a strategy object that implements the Trajectory interface. The Trajectory interface modifies the Entity's state in UpdateState(). The entity class delegates the update of its state to the Trajectory strategy. The problem is that in python, when I implement the Trajectory interface and pass the object to the Entity class, the call to Trajectory.UpdateState doesn't seem to work correctly. It gets executed but the state is not updated. (I guess it has to do with the fact that I'm passing the object as a reference). However, if I call UpdateState directly from the python object that implements Trajectory interface it works fine. (ie. it changes the content of the object) If this is still too much let me know and I'll try to reproduce the error with simpler classes. But here is the code. class Entity { /// specify a trajectory strategy /// which is a shared pointer to a Trajectory object specified below SetTrajectory(const TrajectoryPtr &T) { trajectory = T; } /// delegates to the Trajectory strategy /// the updating the state virtual void UpdateState(double ellapsedTime=1) { t->UpdateState(state,ellapsedTime); } private: EntityState state; ///< object to be modified TrajectoryPtr trajectory; /// this is a shared pointer }; class Trajectory /// interface that i want to inherit in python { public: /// note it takes the state as a reference virtual void UpdateState(EntityState& state, double ellapsedTime) const = 0; }; I exposed the class using pyste and in python I'm derived a class from it. class HackedT(Trajectory): def UpdateState(self, entitystate, ellapsedTime): entitystate.position = gmtl.Point3d(-1,-1,-1) The problem is that when I do this in python: target = Entity() target.SetTrajectory(hackedT) target.UpdateState() # enventually calls the HackedT's UpdateState, which modifies the state print target.GetPosition() I expect the result to be (-1,-1,-1) but instead its coming out to be the original value (10,10,0). However, if I use Trajectory objects created from C++ then the state is modified. Also, if I call the function directly it modifies the state. s = EntityState() ## by default s.position = (0,0,0) hackedT.UpdateState(s,1) print s.position ## returns (-1,-1,-1) Is this a bug in Boost Python or do I have to specify some policy or something to make this work? Let me know if you need additional information. Again, any help will be greatly appreciated, (Hope it's better summarized) Alexis Programming Tutorial: In Python: To do this, do this In Perl: To do this, do this or this or this or this... In C: To do this, do this, but be careful In C++: To do this, do this, but don't do this, be careful of this, watch out for this, and whatever you do, don't do this __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com