C++ to Python

#include <boost/python.hpp>

using namespace boost::python;

//I'm assuming your buffer data is allocated from CSomeClass::load()
//it should return the allocated size in the second argument
static object csomeclass_load(CSomeClass& self) {
  unsigned char* buffer;
  int size;
  self.load(buffer, size);

  //now you wrap that as buffer
  PyObject* py_buf = PyBuffer_FromReadWriteMemory(buffer, size);
  object retval = object(handle<>(py_buf));
  return retval;
}

static int csomeclass_save(CSomeClass& self, object buffer) {
  PyObject* py_buffer = buffer.ptr();
  if (!PyBuffer_Check(py_buffer)) {
    //raise TypeError using standard boost::python mechanisms
  }

  //you can also write checks here for length, verify the
  //buffer is memory-contiguous, etc.
  unsigned char* cxx_buf = (unsigned char*)py_buffer.buf;
  int size = (int)py_buffer.len;
  return self.save(cxx_buf, size);
}