My flow is such that I already have the access token available in my backend server. So basically I was using the REST Apis until now for getting all user messages. However, I would like to use the Gmail API batch requests to improve on performance. I see that it is non-trivial to use python requests to do so. The gmail api client for python on the other hand does not seem to have a option where I can use the access token to get the results. Rather I need to use the authorization code which is unavailable to me. Can someone help me solve this? 
Thanks,
Azeem
You need to activate the Gmail API in your project on Google Developer Console to get the API key which will have separate billing cost involved.
Gmail Python API: Build service using access token