title: binding C++ protobuf message to python
body: <p>I have a C++ API. The API uses Google protobuf to receive message. Now I want to wrap C++ API to python. 
  In python code, I will create protobuf message (same proto file as C++ API) and call C++ API to send. 
  I am using Python SIP to wrap C++  API. But I don't known how to from python call C++ API method with an argument is protobuf message.</p>
  
  <p>Can you help me?.</p>