How to change format from json to protobuf when send response back to doubleclick ?

[SchopenhauerZhang]

I write python api to receive the bid request from google double click , of course ,it is json format .But now I have to change the format from json to protobuf when send response or receive bid requests.
What do i do? I do not know how to write the code after reading the doc of https://developers.google.com/authorized-buyers/rtb/openrtb-guide.
Obviously， google developers' doc is not work. it does not list the details about this situation(change the format from json to protobuf when send response or receive bid requests. ).
So ,i need help about above.