I am a java developer and just now started working in Python. I have written one AWS lambda code in python 3.9. In first attempt I have written the complete code in one or two files. But somewhere I have read that we should not create fat files. Then I try to segregate the code into different folders and files. Folders like handlers, services , utils , dao, entity. Each folder has one file and each file has number of functions which can be called independently from another file through import. Then one of the Python expert told me to apply OOPS concept  and also to follow either DDD design or MVC pattern.
Is it necessary to follow OOPS concept and create classes in serverless architecture?
Can you point me to some sample GIT repo showcasing the framework for developing an object oriented lambda?
AWS lambda gets activated on request and dies down when request is served. It is not like server which is active 24hours without request.
What is best design pattern or architecture or coding paradigm to follow in AWS lambda code for python language which also supports modular programming?
Try writing helper functions into utils.py file so that your lambda_function.py file is not big. You can also write async funtions to reduce timeout error as each lambda has its own execution time out.  Service Pattern will sit the best for these kind of services.You can invoke async function by invoking a lambda inside one lambda.
Which design pattern to follow while writing AWS lambda code in Python 3.9