How to append a value to an option in config file using Python

I have config file as below:

[SECTION]email = user1@exmple.com, user2@example.com

Now i want to append some more email ids in email using python, which should like as given below:

email = user1@exmple.com, user2@example.com, user3@example.com, user4@example.com

Please let me know how to do that.