Hi. I did not have time to review your use of pyplusplus, sorry. But I did reviewed the code you were trying to expose. For your first question, how to empty list, try to use boost::python::slice l = l[ slice(0,0) ] I think this should work About your access violation: I think you get it because of mutli-threading. Python and boost.python are not multi-threaded. May be I missed something, but I would go to an other solution: use std::vector, fill it with data and return it. boost.python has functionality that will help you to wrap such vector. Also I think, that you can change your design a little. Can you implement the whole functionality in pure, no boost.python, C++ and then to create 2 functions: Both of them will return a vector of symbols. Can you do it? Hope this was helpful. I will have much more time in the end of the next week. ( I live according to Jews calendar :-) ) Thanks -- Roman Yakovenko C++ Python language binding http://www.language-binding.net/