static ImmutableTreeVector<T> slice(ImmutableTreeVector<T>& in, boost::python::slice s)
{
int32_t start = boost::python::extract<int32_t>(s.start());
if (start < 0)
start = in.size() - start;
int32_t stop = boost::python::extract<int32_t>(s.stop());
if (stop < 0)
stop = in.size() - stop;
return in.slice(start, stop);
}
